9304

Appliance Repair

Study Unit 4

Electric Heating
Appliances and Fans
By

Jack Darr

Revised By

Robert L. Cecci

iii

Preview

Now that you have completed the study of the fundamentals of appliance repair, we can begin
studying how to repair heating appliances and fans.

In this study unit, you will see how to test and replace components properly. You will see how
to disassemble, test, replace and perform a safety test on various heating appliances and fans.

In this text, you will begin to see how to troubleshoot actual appliances. You will begin by check-
ing power cords. Power cords take the greatest abuse and are the most likely cause of both inter-
mittent and total failure in appliance performance. Here, you will also see how to choose the
correct appliance power cord for each type of appliance.

Next, you will see how to repair electric room heaters. We have already used heaters in pre-
vious texts for examples of the use of test equipment. Now, you will see how to disassemble,
test, and replace heater components. Also, you will see how a heater can be constructed to have
multiple heat ranges.

The next heating appliance to be covered will be the electric clothes-pressing iron. This text shall
cover the disassembly, testing, and repair of dry, steam, spray, and steam/spray irons.

The final two sections of this text will cover room fans, and attic fans/power ventilators. You
will see how to rebuild a fan unit and how to eliminate electrical problems and problems of
noise and vibration.

At the end of this unit, you will be able to

• Describe the features of typical appliance line cords
• Identify the proper type and AWG size of appliance line cords
• Discuss the purpose and application of devices such as strain reliefs, solderless connectors,
and crimp-on lugs
• Describe how typical room heaters are constructed
• List the steps to proper electric room heater servicing
• Describe how electric irons are constructed and how to repair dry, steam, and spray irons
• Identify various types of electric fans and list the steps to proper fan repair
• Determine how to troubleshoot and repair attic fans and power ventilators

v

Contents

WORKING WITH LINE CORDS AND PLUGS . . . . . . . . . . . . . . . . . 1
Appliance Line Cords
Wire Sizes in Line Cords
Zip Cord
Jacketed Cord
Cords Used in Heating Appliances
Selecting Line Cords
Line Cords with Grounds
Polarized Receptacles
Cord Connections
Line Plugs and Replacement
Stocking Replacement Line Cords
Strain Relief
Splicing Cords
Using Solderless Connections
Crimp-On Lugs

ELECTRIC ROOM HEATERS . . . . . . . . . . . . . . . . . . . . . . . . . . 15
How a Heater Works
How a Heater Is Built
Hints for Servicing Room Heaters
Heating Elements
Mounting Heating Elements
Electrical Connections to Heating Elements
Thermostats in Heaters
Testing Heaters
How to Test a Heater for an Open Circuit
How to Replace Heater Parts
Testing after Repairs Are Finished
Reassembling the Heater

COMBINATION OF HEATING ELEMENTS . . . . . . . . . . . . . . . . . . 27
Current in Heating Elements
Resistance of Heating Elements
Multiple-Heat Circuits with Parallel Elements
Series-Connected Elements
ELECTRIC IRONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Operating Features of an Electric Iron
How an Electric Iron Is Constructed
How a Dry Iron Is Built

vi Contents

Thermostats in Irons
Steam Irons
Spray Irons
Check Valves

HOW TO TEST AND REPAIR ELECTRIC IRONS . . . . . . . . . . . . . . . . 41
Testing the Line Cord
How to Repair the Line Cord
How to Take a Steam Iron Apart
How to Take Dry Irons Apart
Continuity Test of Heating Element and Thermostat
How to Remove Bolts and Nuts from an Electric Iron
How to Detect Scale in Steam Irons
How to Clean Steam Irons
Disassembling Newer Irons
Troubleshooting Modern Irons
ELECTRIC FANS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Types of Fans
How Fans Are Built
Fan Blades
Two- and Three-Speed Fans
How to Take a Fan Apart
How to Test the Speed Control
Burned-Out Motor Coils
Dragging Bearings
Worn Bearings
Causes of Noisy Fan Operation
How to Tighten a Loose Hub
How to Check Blade Angles
Adjusting Blade Tips
Loose Parts on Guards
Oscillating Fans
Repairing Combination Light/Fan/Heaters
Air Purifiers
Servicing Air Purifiers

ATTIC FANS AND POWER VENTILATORS . . . . . . . . . . . . . . . . . . . 73
Types of Fans and Ventilators
Servicing Attic Fans and Power Ventilators

CHECK IT OUT! ANSWERS . . . . . . . . . . . . . . . . . . . . . . . . . . 81

EXAMINATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

1

Electric Heating Appliances and Fans

plastic insulation. Appliances which draw a
WORKING WITH LINE heavy current, such as electric irons and heaters,
CORDS AND PLUGS must use a special line cord with heavy wires
and high-temperature insulation.

Appliance Line Cords
Wire Sizes in Line Cords
The wire which connects an appliance to a
wall outlet is termed the line cord by most The size of a wire determines the amount of
appliance technicians. The line cord is a very current it can safely carry, just as the size of
important part. Unless power can get to the a water pipe determines the amount of water
appliance, the appliance will not work. The which can flow through it. The thicker the
line cord is also the part which gets the wire, the greater the current it can carry.
hardest service; it is bent, kinked, crushed, The wire in a line cord should be large
and even cut. enough to carry the normal current without
The line cord is the first thing you should heating up; the heat should be in the appli-
check whenever you test a faulty appliance. ance, not in the line cord. If the line cord
Look for places where the cord may have should heat from an overload of current,
been crushed or even cut. Take the cord and the insulation would go bad in a very short
bend it sharply between your fingers, watch- time, presenting a serious shock hazard.
ing the insulation. If the cord is too old, you’ll The size of a wire is indicated by its gage
see fine cracks in the rubber or plastic insula- number. Wire size is generally specified by
tion at the bend. Such a cord should be re- the American wire gage (AWG), which is also
placed because the insulation will soon fail. known as the Brown & Sharpe gage (B&S).
If the cord isn’t in first-class condition, it An assigned AWG number indicates a certain
could be a very serious shock hazard to the wire size, and the amount of current a wire
user. Since practically all household appli- can carry is termed its ampacity.
ances are accessible to children, you must Table 1 on page 2 shows the standard wire
make sure that the line cord is absolutely safe. sizes used in all appliance cords and the
The cord insulation must be perfect, not safe current-carrying capacity, or ampacity,
aged or broken. All electrical connections of each wire size. Strangely enough, the big-
must be tight and well insulated. ger the wire number, the smaller the wire.
Bad line cords are the most common trouble For example, AWG No. 12 is much bigger
source in all portable appliances. A great than AWG No. 18, and it carries more current.
deal of your work will consist of replacing The standard types of cords, according to
cords. You must know exactly what kind of insulation, are indicated by letters.
replacement cord to use on each appliance. The wire used in the line cord must be able
There are several types of cords available, to carry the normal current drawn by the
and the cord used depends on the appli- appliance, plus a little more as a safety
ance. Small, low-current appliances use margin to keep the cord from heating up.
cords with small wires and with rubber or

2 Electric Heating Appliances and Fans

You learned earlier how to determine the Zip Cord
amount of current an appliance will draw.
From the nameplate, take the voltage and Small appliances, up to 100 to 200 watts, use
the wattage, and then divide the watts by a lightduty rubber-insulated cord, type SV,
the volts to find the current. For instance, if type SPT. Most technicians call this cord a
an appliance draws 1200 watts at 120 volts, zip cord. Its wires are parallel, and there is
it will use a groove between them. This makes it easy
to pull, or zip, the wires apart to make
I = P/E = 1200/120 = 10 amps connections; hence the name “zip cord.”
Most small appliances use zip cords with
wires from No. 18 to No. 14.
Table 1

Size S, SJ HPN Jacketed Cord
AWG SV, SPT HSJO
Heavier appliances that draw high currents,
18 10 10 such as irons and heaters, need heavier wire
16 13 15
and better insulation. They may need a type
of cord designated SV or SJ. If the two insu-
14 18 20 lated wires in the cord have a plastic outer
12 25 25 cover for extra protection, the cord is called
a jacketed cord. The two wires are made so
10 30 30
that they spiral around each other, and
strands of a special paper or fiber are added
between them for extra protection. A jacketed
Looking at Table 1, you can see AWG No. 18
cord is used on washing machines, vacuum
wire is rated at only 10 amp if it is of the rubber
cleaners, and similar appliances which are
type SJ and has two conductors. This wire is
used in damp places. The extra protection is
too small. For safety’s sake, use at least an
needed where the cord must be able to stand
AWG No. 14 wire rated at 18 amp, or better
hard wear, such as being walked on, rolled
still, an AWG No. 12 wire rated at 25 amp. If
up, bent, and flexed. Jacketed SV and SJ cords
you can’t get the size wire you want, always
are made in sizes No. 18 and No. 16. Heavier
use a wire of the next larger size or next smaller
jacketed cords, such as Type S with wires up
AWG number, and you can’t go wrong.
to No. 10, are available for extra-hard use in
Besides the greater ampacity it provides, there damp places.
is another advantage to selecting a line cord
with wires somewhat larger than necessary.
The flexible line cords are all stranded. That Cords Used in Heating
is, many strands of much smaller wire make Appliances
up a wire of a larger size, the number of
A special type of cord is used on heating
strands depending on the cross section of
appliances where currents are higher and the
each individual strand. The strands will
cord may be burned if it should come in contact
inevitably break in use some day. However,
with the heater. This cord is called the heater
if you use a No. 12 wire where only a No. 14
cord. The wires are insulated with ethylene
is needed, by the time enough strands break
propylene rubber or polychloroprene, and
to bring the wire down to the cross section
strands of fiber glass are sometimes added
that will carry as much current as a No. 14
between the wires. The older heater cords
size, the cord will have lasted much longer
are covered with a heavy woven cloth braid.
and been much safer.

Electric Heating Appliances and Fans 3

Heater cords are available with wires from order wires large enough for the job. In your
No. 18 to No. 14, and among the standard repair work, you will seldom need a cord
types are HPN and HSJO. with wires smaller than AWG No. 14.

Selecting Line Cords Line Cords with Grounds
When some strands in a stranded wire break,
In Figure 1 are shown the three types of line the cross section of the wire in the line cord
cords, the heater cord, the zip cord, and the becomes smaller and the cord will get very
jacketed cord. The jacketed cord is shown hot when the appliance is turned on. If all
with three wires; the third wire is used for strands in the cord break completely, an arc
grounding the case for safety. will form across the very small gap between
the ends of the strands and generate high
heat which can melt the insulation on the
wires, cause a short circuit, and even burn
the cord completely in two.
In older hand-held electrical appliances, such
as electric drills, saws, and mixers, the break-
down in the cord can cause the hot wire to
come in contact with the metal frame or the
case of the appliances. This short circuit
can give the person using the appliance a
dangerous shock. A safety cord, called a
grounded line cord, has been developed to
FIGURE 1—Three different types of appliance
power cords are shown here. eliminate this danger. Such a cord has the
two regular wires needed to complete the
Standard flexible cords are designated by circuit, plus a third wire connected to the
letters as indicated in Table 1 on the preceding frame of the unit, as shown in Figure 2 on
page. You may select the cords according an electric drill. This “grounding wire” is
to place of usage, such as in dry or damp connected to the frame of the drill and to
places; or according to degree of usage, such
as “extra-hard usage,” “hard usage,” and
“not hard usage.” For example, rubber- MOTOR
covered cords SV and SJ are available with
No. 18 wires. Both may be used in damp
places, but the Type SV is for “not hard usage,”
that is, it is used for smaller vacuum cleaners
and food mixers, while the Type SJ is for
ELECTRIC DRILL
“hard usage,” as in larger vacuum cleaners.
A similar rubber-covered cord, Type S, is for
“extra-hard usage”; it resists alkalies, acids, GROUNDING WIRE
and water, and is available with wires AWG
No. 18 to No. 10. MOTOR
WIRES
Most of the time you will select cords from
catalogs which indicate the insulation, the FIGURE 2—When an appliance has a three-wire
best application, the wire sizes, and the prices power cord, the green wire is grounded and will
of available cords. But always remember to attach to the case of the appliance.


the ground pin at the plug. The plug on the The circuit opens, the appliance is cut off
line end of the cord has a round third prong from the source, and the user is protected
to which the grounding wire is connected. from a possible shock.
The two regular circuit wires are connected
to the two flat prongs. Such a special grounded Most modern appliances and power tools
plug and a grounded outlet are shown in use plastic cases. Since plastic is an insulator,
Figure 3. The round prong prevents this line the shock hazard present with metal-cased
plug from being plugged into an outlet which appliances and power tools is eliminated.
does not have the ground as a safety feature. Many of these devices will, therefore, use a
The grounded or polarized outlet has a third simple two-wire power cord. If a three-wire
hole, or terminal, for the third prong. This cord is used, the ground lead is normally
hole is D-shaped. attached to the case of the motor inside the
appliance or power tool.
Most older electrical appliances of all kinds
are equipped with a grounded line cord
and a grounded plug. To accommodate them, Polarized Receptacles
old outlets with two terminals must be
replaced with the newer grounded outlets, Many outlets, or receptacles, in older homes
which have an additional terminal for the will not have the third terminal for the
prong of the grounded plug. If you expect grounding prong of the cord. If you replace
protection from the grounded line cord, these receptacles, you should buy polarized
you must connect the third wire to the receptacles which make the use of the ground-
ground, that is, from the round terminal ing cord possible. A polarized receptacle is
of the outlet to the ground. recognizable by the three terminals, one of
which is D-shaped and marked “ground.”
The idea behind all this is simple: If the
appliance develops a short circuit (if a wire When replacing a two-wire outlet with a
accidentally makes contact with the appliance three-wire, or polarized, outlet, you must
case), an arc will form between the broken connect the third-wire terminal to a grounding
wire and the grounded wire in the cord, the conductor, or the outlet won’t offer any
high current will flow back through the protection at all.
circuit to which the outlet is connected and
blow the fuse or trip the circuit breaker. Standard color-coding of house wiring is
black for the hot side and white for the neutral;
the third wire may be green or bare, and is
grounded. In the three-wire line cords, this
same color code will be followed, and the
third wire will always be green. However,
do not depend on color-coding. The house may
have been wired by an amateur electrician
ignorant of the proper coding. Test the
wiring to be sure.

Cord Connections
The connections on both sides of the line
FIGURE 3—A three-wire cord and plug are shown cord are very important. They must be clean,
here. Notice that the plug uses a polarized outlet tight, and strong at both ends, so that the
with different-sized blade receptacles.


cord won’t loosen in service and cause a short
circuit. The stranded wire of the cord can be
hard to handle unless the right methods are
used. Later you will learn how to make
connections with stranded wires.

The appliance is connected to the line cord (a) (b)
through screwed, soldered, or crimp-on
terminals, or through a receiver plug. The
line side of the cord has a line plug which
is to be connected to the wall outlets.

(c)
Line Plugs and Replacement (a) First step
(b) Second step
(c) Incorrect method
You can buy a prefabricated line cord for
small appliances up to about the size of
vacuum cleaners. The line plug is molded FIGURE 5—The replacement of a plug is shown
here. (Courtesy of McGraw-Hill Book Company, Inc.)
onto one end of the cord, and the other end
is already prepared, with the wires stripped
and fastened to lugs, as shown in Figure 4. up, though, it won’t be long before the wires
Such cord is used by most appliance techni- pull out. Figure 5 shows the procedure for
cians to save time. fastening the wires to one type of plug.
Here’s how to do it.
In many jobs, however, you will have to put
a plug on the end of a new line cord or replace If you have a zip cord, pull the wires apart
a plug that has broken connections on the for a distance of about two inches. Strip off
original cord. You must know how to install about 2.5 cm (1 in.) of insulation on each
a plug. Correctly installed, a line plug will wire. You’ll see that the fine strands of the
last a long time. If it isn’t correctly hooked wire are twisted inside the insulation. Twist
the free ends in the same direction, to eliminate
the possibility of a short circuit or shock
hazard. Now, feed the ends of the wires
through the hole in the end of the plug, up
between the prongs.

Tie a knot in the two wires as shown in
Figure 5(a), leaving about 3.5 cm (1.5 in.)
of wire extending beyond the knot. The knot
provides strain relief and holds the wire tightly
inside the plug, as shown in 5(b), so that if
the cord is pulled, there won’t be any strain
on the electrical connections. Never fasten
the leads without making a knot as shown
in 5(c). The steps in tying this knot are
shown in Figure 6.

FIGURE 4—A replacement line cord is available Next, wrap each wire around one of the
with special lugs attached for easy connection prongs and then around the terminal screw,
to an appliance. which should be loosened about two turns.


plug body. Sooner or later, the wires will
break. When the cord is moved one way, the
ends of the break are pushed together and
the plug works; when the cord is moved the
other way, they pull apart and the circuit is
open. For a quick check, hold the plug in one
hand and move the cord back and forth. If
the appliance suddenly starts and stops as
the cord is moved, wires are broken. Replace
FIGURE 6—A zip cord should have a knot tied in it
the plug.
to provide strain relief. (Courtesy of McGraw-Hill Book
Company, Inc.) Replacement plugs are readily available. Two
types of replacement plugs are shown in
Be sure to wrap the wire in a clockwise Figure 8. The plug on the lower left is used
direction around the screw, as shown in for thin two wire or zip cord. To install this
Figure 7. If you wrap the wrong way, when type of replacement plug, the halves of the
you tighten the screw, the wire will be plug are separated and the unstripped zip
squeezed out from under the screwhead. But cord is placed inside one half of the plug.
if you wrap the right way, the screwhead will Then, the second half is squeezed onto the
pull the wire tighter. Be sure that all strands wire until the locking tabs inside the plug
of the wire are under the screw, so that you catch. Teeth within the plug pierce the insu-
won’t lose any of the wire’s current-carrying lation of the zip cord to make electrical
capacity. Remember that loose strands of contact with the wires inside the zip cord.
wire in plugs or in any other electrical con-
nection are an invitation to a short circuit.

Molded plugs come as original equipment
on many appliance cords. Such plugs are
usually made of rubber or plastic, as shown
in Figure 8 (item 1). The most common
user’s complaint about this plug is that
sometimes it works when it is plugged in
and sometimes it doesn’t. Here’s what hap-
pens. As the cord is pulled back and forth, it
bends at the point where it comes out of the

FIGURE 8—Two types of replacement plugs are
shown here.

RIGHT WRONG
The replacement plug on the upper right is
a heavy-duty three-wire plug. The front and
rear of the plug are separated by loosening
the screws on the front side of the plug. The
wires are then placed on their proper termi-
nals and the internal screws are tightened
to hold the wires. The front screws are then
FIGURE 7—The correct method of attaching a tightened to hold the plug halves together.
wire to a terminal is to wind the wire in a A clamp in the rear of the plug also has two
clockwise-direction, hook the wire around the
screw, and tighten the screw. (Courtesy of McGraw-
Hill Book Company, Inc.)


screws that are tightened to firmly clamp Stocking Replacement Line
the wire at the rear of the plug.
Cords
Since most bending and flexing takes place
at the plug end and at the point where the When you’re starting in the appliance repair
line cord enters the body of the appliance, business, it is a good idea to stock about half
you’ll find practically all of the accidental a dozen ready-made line cords with plugs.
breaks in line cords at one of these points. Later on, you can buy the right kind of cord,
In fact, many technicians, when they find in full reels, and a stock of plugs, and assem-
an open line cord by testing, simply cut the ble the line cords and plugs as you need them.
cord at a point about 15 cm (6 in.) from the This saves a little money. You can also make
plug. They strip the wires and test again. If the replacement cord longer than the original
they now get continuity in the cord, they line cord if the customer wants it that way.
replace the plug and the job is done; if not,
they replace the whole cord, since it is
obviously open at the other end or some- Strain Relief
where in between the ends.
An appliance usually has an attachment
Many appliance repair persons are now using which holds the cord in place and relieves
a two-piece plastic replacement plug. This strain on the electrical connections. Such an
plug uses a compression system to hold the attachment is called the strain relief. There
wires to the plug’s terminals. To use this type are several different kinds of strain-relief
of replacement plug, you strip the outer jacket devices, but they all serve the same purpose.
cover back approximately 4 cm (1.5 in.) and
strip 6 mm (.25 in.) off the wires. Place each If the appliance case is metal, the cord needs
wire into its proper terminal and tighten the some protection to keep the sharp edges of
screws. The terminal’s screws are normally the hole from cutting the insulation. A small
color-coded so that it is easy to install the soft-rubber grommet is pushed into the hole,
wires to the proper terminals. The green as shown in Figure 9(a). The cord passes
screw is always used for the green wire through the grommet, and an overhand
which is grounded. The silver screw is used knot is tied on the inside to keep the cord
for the white wire which is neutral. Finally, from being pulled through again. When you
the copper-colored terminal is used for the are replacing the cord, always leave a little
black wire which is the AC feed of 120 VAC. slack in the wire between the knot and the
electrical connections.
To complete the assembly, one of two types
of strain relief will be used on the plug. One In some appliances you’ll find the grommet
type uses a tapered barrel and rubber or foam and a small metal clamp which holds the cord
insert. This type of strain relief is installed to the side of the case, as in 9(b). Others will
by simply tightening the tapered barrel onto use a plastic strain-relief device, which is
the plug assembly. As the barrel is tightened, folded over the cord and then pushed into
the rubber or foam insert is compressed the hole, as shown in 9(c). The insulation
around the wire. is compressed, then it snaps back, and the
device is held in place by notches molded
The second type of strain relief uses a split in its sides. This device is used mostly with
rear barrel which is tightened around the the flat SJ cord or the zip cord, but you can
wire by means of two screws. find larger sizes for use with round SV cords
and larger cords.


CASE
RUBBER GROMMET
KNOT

(a)

RUBBER GROMMET

METAL CLAMP

(b)

PLASTIC STRAIN
RELIEF

(c)

FIGURE 9—Three types of strain relief are shown here. In (a) and (b), you can see a soft rubber grommet
being used. In (c), a split grommet is being used.

If an appliance does not have any strain pro- Splicing Cords
tection, add such protection. If the hole isn’t
large enough to take a grommet, enlarge the If you find that the line cord of an appliance
hole and put a grommet in. The appliance is broken in the middle, examine the cord
will be much safer. very carefully. If the insulation on the whole
cord is even slightly cracked, replace the
whole cord. Making a splice in a cord is the
exception and not the rule.


There’s an easy way to make a splice. Always on the other. Now, strip the insulation off all
remember that the splice must be as strong the wires, for about 2.5 cm (1 in.) or less. Many
as the rest of the cord, and perfectly insulated. professionals strip wires with a wire stripper
With modern tapes and methods, it is possible like the one shown in Figure 10(a).
to make small neat splices that will last.
Here’s how you do it. Hold the insulation between the stripper
jaws as shown in 10(b), without applying
Cut the cord at the break. Strip off about 5 cm too much pressure, so as to avoid cutting
(2 in.) of the outer jacket, using a sharp knife. the wires. Then give a sharp yank toward
Next, hold the two ends of the cord together the end of the wire; the insulation will come
and cut off 2.5 cm (1 in.) of the black wire on off, leaving the wires exposed. This takes a
one end and 2.5 cm (1 in.) of the white wire little practice, but it is the fastest way.

FIGURE 10—A typical wire stripper and crimper is shown in (a). Figure (b) shows how to strip wire with this
tool. (Photos Courtesy of Robriair Manufacturing Company)


If the wire is clean, start splicing. If it has on a single layer of tape. When you get to
darkened with age, it is a sign to replace the other end, cut the tape off and smooth
the wire. To splice the wire, place the ends it out. Next, put on the final layer in the other
of the black wires together, and twist the direction. Pull the tape as tight as possible so
bare parts over one another. Be sure that all that the splice will be well insulated. If this
strands are in place. The splice should not cord will be used in a damp place, spray a
be thicker than 12 mm (.5 in.) of bare wire. thin coat of acrylic plastic over the whole
Solder the splice smoothly. Be sure that the splice. This will seal the tape very tightly
solder runs well into the wire. If solder is and make your splice as waterproof as the
exposed, either melt the solder again or file original cord.
the sharp points off before taping. Such
points could punch through the tape and
cause a shock hazard or short circuit. Using Solderless
After soldering, tape the splice. It is easier to Connections
tape one completed splice before you splice
the other wire. Use plastic electrician’s tape Inside many appliances, you’ll find solderless
and wrap the tape neatly over the bare parts connectors like the one shown in Figure 12(a).
of the splice, going up over the insulation at These are little bell-shaped devices made
both ends. Stretch the tape over the splice of insulating material, usually plastic, and
almost as smoothly as the original insulation. often called wire nuts. They are used mostly
Two layers of tape are enough. on small stranded wires. Large sizes are
available for use on solid wires, such as the
Next, splice the other wire just as you did types used in house wiring.
the first one, pulling the wires apart in a
“bow” so that you can reach the wire being You can connect up to four wires with a
spliced without melting the tape on the first solderless connector, depending on the size
wire. Tear off a short piece of tape because connector used. To make a connection like
you’ll have to thread this tape through the this, strip the ends of the wires back about
loop of the two wires. 6 to 10 mm (.5 to .75 in.) and put them side
by side with the bare wire ends parallel, as
Now you can see why we cut the two wires shown in 12(b). The ends of the insulation
at odd lengths: the two splices are staggered should be exactly the same length.
(they are not next to one another) as shown in
Figure 11. This staggering lets you put on the Now, put the wire ends inside the open end
final wrap of tape without leaving a big lump of the wire nut shown in 12(c). Screw the wire
in the cord. Start the taping well back up on nut on in a clockwise direction because it
the jacket, about 2.5 cm (1 in.) or so, and wrap has a right-hand thread. The small metal

FIGURE 11—The proper method of winding the wires for an inline splice is shown here. Crimp-on inline
sleeve splices may also be used. (Courtesy of McGraw-Hill Book Company, Inc.)


THIMBLE
SPIRAL SPRING

(a)

(b) (c)

FIGURE 12—A typical wire nut is shown in (a) with the correct method of installing the nut in (b) and (c).
(Courtesy of McGraw-Hill Book Company, Inc.)

spring inside the wire nut, shown in 12(a), then replace the connector with a wire nut.
will catch the wires and pull them up inside The connection will be just as good as the
the insulator. Keep on turning until the original.
connection is very tight. Make sure that the
insulation of all wires is covered by the flared Crimp-On Lugs
end of the wire nut. If it isn’t, a short circuit
may develop later on. In many appliances, especially those using
screw terminals, you’ll find a special kind of
The solderless connector is especially handy terminal lug called a crimp-on lug, which can
because it can be taken apart for testing and be attached without soldering.
then put back without the use of tools. In
some appliances, you may see connectors The crimp-on lug has a hollow sleeve for the
which look like wire nuts but aren’t. These wire and a lug which will serve as a terminal.
are the crimp-on types which are permanently Strip the wire just enough to go through this
attached by crushing the sleeve inside the sleeve, no more. Push the wire through the
insulator. These can’t be taken apart and put sleeve, making sure that the insulation is
back. However, if necessary, you can cut tight against the end of the terminal and that
such a connector off, make your tests, and the ends of the wire do not go through too far.


In factories the crimp-on terminals are
installed by a machine. In your shop, you
can crimp the sleeve by using the crimp-on
tool, which is the top part of the wire stripper
shown in Figure 13. Pull hard on the crimp-on
connector to make sure that it does have a
good grip on the wire.

Solderless crimp-on connectors are available
in several different types, such as spade lugs,
ring lugs, wire connectors like the wire nuts,
and splicing sleeves.

When a splicing sleeve is used, the two wire
ends are pushed into each end of the sleeve
until they overlap, and then the sleeve is
crimped. An insulator sleeve can be slipped
over the finished joint or the joint can be
taped. Splicing sleeves can save time if you
don’t want to heat up a soldering iron or
don’t have one with you.

FIGURE 13—Crimp-on terminals of many different


✔
Check It Out! 1
At the end of each section in your Appliance Repair text, you will be asked to pause
and check your understanding of what you have just read by completing a “Check It
Out!” Writing the answers to these questions will help you review what you have
studied so far. Please complete Check It Out! 1 now.

1. What is the most common trouble source when a portable appliance does not work?

_________________________________________________________________________
2. Why is defective insulation on a line cord dangerous?

_________________________________________________________________________
3. What is meant by No. 16 AWG wire?

_________________________________________________________________________
4. Define ampacity.

_________________________________________________________________________
5. Which wire carries more current, AWG No. 12 or AWG No. 14?

_________________________________________________________________________
6. What happens if the wire in a line cord is too small?

_________________________________________________________________________
7. What kind of insulation is used on heater cords?

_________________________________________________________________________
8. Why are some line cords equipped with three wires and a three-pronged plug?

_________________________________________________________________________

9. To what should the grounding wire in a line cord be connected?

_________________________________________________________________________
10. How can you recognize polarized, or grounded, outlets?

_________________________________________________________________________

(Continued)


✔
Check It Out! 1
11. What relieves strain on the wire in a line plug?

_________________________________________________________________________
12. Why are line cords made with stranded wires?

_________________________________________________________________________
13. If you cannot get the original size wire for a line cord, what size should you select?

_________________________________________________________________________
14. When you connect a wire to a screw terminal, how should you wrap the wire
around the screw?

_________________________________________________________________________
15. Why is a grommet used in appliances?

_________________________________________________________________________
16. What is the probable cause of trouble if an appliance works at certain times and
fails to work at other times?

_________________________________________________________________________
17. How many layers of tape are used for splices?

_________________________________________________________________________
18. What are wire nuts?

_________________________________________________________________________

19. What are crimp-on lugs?

_________________________________________________________________________
Check your answers with those on page 81.


element rated at 600 watts. This higher-out-
ELECTRIC ROOM HEATERS put element would have half the resistance
of the 600 watt element.

How a Heater Works If the voltage supply is constant, the high
current is obtained by low resistance of the
One of the simplest of electrical appliances heating element. The lower the resistance,
is the electric room heater. The main part of the higher the current, and the greater the
the heater is the heating element, or heating heat produced by the heater if the voltage
coil, which is made of special resistance wire. remains the same. Electric heaters are rated
When voltage is applied to the heater circuit, in wattage, such as 500, 750, or 1000 watts.
a current passes through the heating element The higher the heater wattage, the more
and causes it to get hot. The rate of heat heat it produces. A heating element should
developed in the heating element depends always be replaced with a new one of the
on the electric power drawn by the heater. same wattage, so that the unit will produce
Remember that electric power, or wattage, the same heat as it did when it was new.
is a product of voltage and amperage. Wall
outlets supply alternating current at 120 VAC
to the heating coil. If the current is high, the How a Heater Is Built
power will be high, and the generated heat
will be high. For example, if a current of 10 Each basic room heater is enclosed in a heavy
amps (amperes) flows through the heating metal case. A common heater is shown in
element, the power drawn by the heater is Figure 14. Grilles or screens cover the openings
120 × 10 = 1200 watts and the heat will be so that the heated air can circulate to the
double the heat produced by a 5-amp room. Metal reflectors are used to direct the

FIGURE 14—This heater is typical of the many different types of ribbon
element heaters.


heat where it is wanted. Some heaters have with mica sheets or ceramic pads so
small fans which force out the hot air. The that the heating element can’t touch
air then circulates faster around the heater the frame or case.
and heats the room quicker.
3. Safety switches, thermostats, and other
Heating elements are mounted on heat-proof safety devices must be checked to make
insulators to keep them from making electrical sure that the contacts are not welded
contact with the metal case. In Figure 14, the together or stuck so that they would be
heating element is wound diagonally up useless.
and down inside the case. The heating
elements are made of special wire which 4. All electrical connections, such as the
has certain resistance and is able to with- connection of the line cord to the heat-
stand high temperatures without melting. ing element, must be very clean and
An electric heater may be provided with tight, to avoid developing heat where
a switch that turns the heater on and off. it is not wanted. A hot joint will heat
Some heaters have a thermostatic switch in up and oxidize rapidly when carrying
addition to the on-off switch. The thermostatic the heavy current needed in the heating
switch, or thermostat, turns the heating element, and will burn up.
element off automatically when the room 5. When replacing ON/OFF switches, be sure
reaches the proper temperature. Some other that the new part has the same rating as
heaters have safety switches which turn the the original switch. The rating must be
power off if the heater should be tipped over. high enough to do the job. For instance,
This is done to prevent any fire hazard. some toggle switches are rated 5 amp
at 120 volts, which means a power of
5 × 120 = 600 watts. If you put one of
Hints for Servicing Room these on a 1500-watt heater, it will fail
Heaters in a very short time. Always use parts
which have ratings at least 1.5 times
Before we discuss actual units, there are a the maximum current needed by the
few rules which apply to all resistance wire particular appliance. At 120 volts, the
heaters: current through a 1500-watt heater is
1500/120 = 12.5 amp. The rating should
1. The line cord for room heaters rated therefore be at least 1.5 × 12.5 = 18.75
above 500 watts should be high- amp. Use a standard switch rated 20
temperature heater cord. For safety, the amp at 120 volts. You know that this
wire in this cord must be large enough switch will work safely and last a long
to carry at least 1.5 times the normal time.
current. Insulation on line cords must
always be in perfect condition, to avoid
shock hazard to users. Heating Elements
2. Heating-element support insulators Electric heating elements are usually made
must be replaced if they are cracked. If of a special nickel-chromium alloy wire
the heater uses open wire as a heating called Nichrome, or from a tungsten-based
element, the wire must be tight, so that material. These metals have a very high
it can’t sag and touch the metal frame melting point, which is necessary because
or case. Enclosed heating elements, the metal gets red hot when in use. Copper
like those used in electric irons or wire oxidizes very quickly if red hot and
coffeepots, must be very well insulated will burn up in a short time. Nichrome wire


and other special alloys will stand many
heatings and coolings without too much
oxidation. This wire has a higher resistance
than copper and other metals, and it there-
fore, takes a shorter length of Nichrome or
tungsten wire to make up a heating element.
In the electrical business, heater wire is often
called resistance wire.
A heating element can be made of round wire
coiled like a spring, or of flat ribbons of various
sizes. Some elements are made of bare wires
mounted on insulators. Others are sealed
elements which use resistance wire insulated
with a ceramic material and placed inside
a metal tube which looks like a pipe. Sealed
elements must be used in any application
where the surface of the heating element
must be grounded, as in electric ranges and
water heaters.
FIGURE 15—A ceramic heater uses a special
Resistance wire has two special characteristics ceramic heating element and many safety
that you must remember. First, since it gets devices. (Courtesy of Rival Manufacturing Company)
red hot while heated, you can’t use any rubber
or plastic insulation on it. The element will
not only be hot in the physical sense, but push it out, and replace it with a bolt and
electrically “hot” as well. All insulators used nut, and connector.
must be able to withstand the high heat and One type of modern electric room heater is
at the same time give enough electrical insu- the ceramic heater. A typical ceramic heater is
lating protection. As mentioned, open-wire shown in Figure 15. The ceramic heater has
and sealed elements in heaters use insulators a resistance element encapsulated in a ce-
of ceramic material. Elements in electric ramic material. A fan is used to move air
irons and coffeepots use flat sheets of mica through the ceramic heating element. This
or preformed ceramics. type of heater also normally has many
Second, you can’t solder resistance wire. safety devices such as overload switches
One reason is that the heating element heats and tip-over switches, along with switches
to a temperature higher than the melting to select fan only, or fan with heat and an ad-
temperature of solder. Another is that solder justable thermostat.
will not stick to the wire, because of its com-
position. Therefore, all electrical connections
must be made tight mechanically; that is, with Mounting Heating Elements
bolts, nuts and special connectors.
A typical coiled heating element mounted
In some of the cheaper appliances you’ll on ceramic insulators in a small space heater
find the electrical connections are made by is shown in Figure 16. The coil is tight be-
riveting together the ends of the heater wire tween the insulators; this is a key point to
and the line cord. To replace this kind of remember.
connection, file off one side of the rivet,


insulating shoulder washer which fills up
the hole in the metal frame so that the bolt
can never make electrical contact with it.

The most important part of this connection
is the insulation between the bolt and the
frame. The shoulder on the insulating washer
must be in good shape, so that it will fill the
hole with insulation. Sometimes you’ll find
that this shoulder has been crushed by care-
less installation, or broken off. If so, put on a
new one. Mica washers are often used, but
they are very brittle and must be handled
with care. They will stand high pressure as
long as it is applied properly, but you can
break them when they’re loose.

When preparing a joint, put the shoulder
FIGURE 16—Since the coiled wire heating element washer in the hole first. Then slip the flat
carries 120 VAC, the element must be supported
by insulators such as the ceramic insulators metal washer and flat insulating washer
shown here. over the bolt, and put the bolt through the
hole. Put the other flat metal washer over
An exploded view of a complete room the bolt, and run the first nut down with
heater is shown in Figure 17. It has a ribbon- your fingers to hold all of the insulators in
type open element wound between bars of place. Tighten the nut with a socket wrench,
ceramic material. You’ll find similar heaters holding the bolt with a screwdriver. Don’t
using coiled elements. As long as the total use too much force, or you’ll crush the mica
wattage and length are the same, there is no washers. Before you continue your work,
difference between the ribbon and coil type; test the connection to be absolutely sure
one could be used in place of the other. that it is not shorted to the frame.

Now put on one of the flat metal washers,
wrap the wires clockwise around the bolt,
Electrical Connections to and put on the other flat metal washer and
Heating Elements the second nut. Be sure that the insulation
on the line cord is as close as possible to
All electrical connections to heating elements the connection. Don’t let any of the insula-
must be clean and mechanically very tight. tion get between the washers. Tighten the
connection down until it is firm, but not too
You’ll find many connections made with a
tight. If the connection is too tight, you’ll
bolt, using two nuts and flat insulating and
crush the wires or make them squeeze out
metal washers, as shown in Figure 18 on
between the washers. With only very little
page 20. The first nut is used to hold the bolt
practice, you’ll learn just how much force
tight to the metal frame or bracket, and the
to use.
second nut is used to make the electrical
connections. The bolt must be completely A connection prepared as just described for
insulated from the metal bracket or the frame a small room heater is shown in Figure 19(a)
of the appliance. This is done by using flat on page 21. The heating element is connected
insulating mica washers between each end to one end of the bolt, and the line-cord wire
of the bolt and the metal, and a special is connected to the other end, on the opposite


FAN BLADE
MOTOR

HANDLE
RIBBON
TAKE-UP REAR COVER
CHROME ELEMENT PROBE
INSULATOR ASSEMBLY SWITCH
GRILLE
WRAPAROUND
REFLECTOR
PAN

SWITCH

THERMOSTAT BLOCK
KNOB INSULATOR
SECONDARY
ELEMENT CORD

THERMOSTAT

FIGURE 17—Notice the many components used in an electric room heater. (Courtesy of Arvin Industries, Inc.)

side of the bracket. Does this make any materials will with successive heating and
difference? Not at all; the bolt makes electrical cooling cycles.
contact between them.
The most important consideration in using
A close-up view of one of these terminals is the stainless steel terminals is that the crimp
shown in Figure 19(b). The mica washers be- is tight on the wire. Special crimping tools
tween the first nut and the metal frame are are available for tightly crimping stainless
clearly visible. The second nut and washers steel terminals. Also, many heavy duty
hold the line-cord wire. Many modern resis- crimpers, such as those on a large pair of
tance-wire type heaters will use crimp-on electrical lineman’s pliers, can be used.
terminals for the power line connections to
the heating element. These terminals are
usually made of a stainless steel alloy. Why Thermostats in Heaters
stainless steel instead of copper terminals?
Stainless steel has many advantages. First, As you progress through this course, you’ll
stainless steel can be heated and cooled learn that thermostats are used in many
thousands of times without the annealing, different appliances. You should know how
or softening of the metal. Second, stainless they work. The name “thermostat” means
steel does not oxidize, or discolor and rust, “constant heat” (thermo = heat and stat =
as most other standard crimp-on terminal constant). Thus, a thermostat is a device


CORD
INSULATION SECOND NUT

FLAT METAL WASHERS

FIRST NUT
STRANDS OF
BARE WIRES FLAT METAL WASHER

INSULATING SHOULDER WASHER

METAL BRACKET OR FRAME
FLAT INSULATING WASHER

FLAT METAL WASHER

BOLT

BOLT HEAD

FIGURE 18—The connection to a heating element may be made by means of a bolt and a series of insula-
tors and nuts.

which is used in heating devices to keep the different rates when heated. Such a blade is
heat at a constant level. shown in Figure 20(a) on page 22. The two
different metals are indicated by 1 and 2.
A thermostat switches off the power supplied One end of the blade is held in a clamp.
to the heating element when the temperature When the blade is cool, it is straight. If it is
increases above a certain level, and it turns heated, metal 2 expands much more than
the power back on when the temperature metal 1. Therefore, the blade bends from the
falls below a certain level. The thermostat “push” of metal 2 against 1, as shown in 20(b).
can operate at any given temperature, at a
very low temperature in refrigerators and Heat can be applied to the blade in several
at a very high temperature in furnaces, ways. In the simpler thermostats, the current
depending on the type and setting of the passes through the blade itself. The heating
thermostat itself. effect developed by the blade resistance
controls the bending. If the heater draws
Each thermostat has a temperature-sensitive too much current, it becomes too hot. If a
element. This is usually a bimetal blade. A pair of switch contacts are attached to the
bimetal blade is a flat metallic strip made free end of the blade, as in 20(c), they will
of two different metals which expand at open when the blade bends due to high


FIGURE 19—The connections to a coiled-wire type heater are shown in (a) and magnified in (b).

temperature. This turns the heating element the type of appliance. For instance, a drop
off, and the temperature drops. When the in temperature would close the switch of
blade cools off enough, it straightens, the a heating unit, while a rise in temperature
switch contacts close, the current starts would close the switch of a cooling or
flowing again, and the heater gets hotter. refrigeration unit. Thermostats can be made
to work due to a small or a great change in
In more elaborate thermostats, a separate temperature. The exact characteristics of the
heating coil is placed under or around the thermostats differ in various types of heaters.
blade. The electrical contacts are attached to
the blade but may be insulated from it. No
current passes through the blade; the blade
is heated by the coil. The actual control of Testing Heaters
the electrical circuit is done with relays hav-
The testing of electric heaters is very simple.
ing heavy-duty contacts, since heavy cur-
Turn the heater on and see if it gets hot. If it
rents must be switched on and off. In this
doesn’t, you should test to find out why it is
way, the thermostat blade can be made
not working. If there is a short circuit, it will
much more sensitive to small changes in
blow the fuse or trip the circuit breaker. This
temperature.
is one of the easiest faults to locate because
You’ll find thermostats in all shapes and it has very obvious symptoms. If the heater
sizes. Some will have coiled-spring blades doesn’t get hot when plugged in and turned
instead of flat blades. However, they all on, then there is an open circuit somewhere
work in the same way. A rise or fall in tem- in the heater circuit.
perature causes the blade to move, opening
Before going any further with testing the
or closing an electrical contact and acting as
heater itself, make sure that the heater is
a switch. The particular action depends on
supplied with the proper voltage. This test


CLAMP

1
2
(a)
CLAMP

1
2
(b)

CURRENT
CLAMP ELECTRICAL
CONTACTS
1
2

(c)
FIGURE 20—Because of the use of dissimilar metals, the thermostat will move when heated. Notice the
difference between the cool blades (a) and heated blades (b). Figure 20(c) shows a set of contacts
connected to the blades.

should be made first when testing any elec- should be replaced if it does not hold the
trical appliance. It can save time. No appli- plug prongs tightly.
ance can work if it does not receive voltage
from the wall outlet or from another source.
The fastest way to check the wall outlet is to How to Test a Heater for an
measure the voltage. If the voltage measures Open Circuit
around 120 VAC, then you know that the
voltage is available and that the circuit fuse After making sure that a normal voltage
is not blown nor the breaker tripped. supply is available at the wall outlet, you’ll
have to take the appliance apart to get at the
When you plug in an appliance, note how electrical connections. For safety, these
the line plug fits into the outlet. It should connections are always on the inside of the
not slip in too easily. You should always feel appliance. First, be sure that the line plug
some friction as the prongs of the plug slide is pulled out of the wall outlet and lying
between the spring contacts inside the outlet. where you can see it. Now, you can work
This friction is absolutely necessary for a and test in safety.
good connection. Old and worn outlets
account for many electrical troubles when Most small heaters are housed in metal cases
their contacts become loose. The outlet with grilles for better air circulation. The
grilles are held in place with small screws


at the corners or edges. You’ll be able to see across the switch should be cause for switch
through the grille to test the connections. replacement. The reason for the replacement
When you remove the grille or any cover, of the switch is that heat caused by the resis-
put the screws, knobs, and all small parts tance within the switch will cause the switch
you take off into a little box, so that they’ll to fail in a short period of time.
all be readily available when you are ready
to put the heater back together. This simple The final test to make is across the heating
measure can save a lot of time, and time is element. Typical resistance-wire type heaters
money. are in the range of about 4 to 20 ohms
depending upon the wattage of the heating
If the heater has three parts, the line cord, element.
the switch, and the heating element, you
have three possible sources of trouble. We have described these tests in detail so
Always remember the following rule, which that you can get used to the procedure of
applies in every case of electrical trouble: testing. Actually, in any of the open-wire
There are as many possible causes of heating elements, you won’t need any test
trouble as there are parts in the circuit. equipment to find an open element, except
your eyes. A break in the element will be
Tests of the three parts are shown in Figure 21. easy to see. However, if the element isn’t
The safest tests are continuity or resistance visible, or if it is one of the sealed types, you
tests which can be made with the power must use electrical tests to locate the trouble.
removed from the heater.

The first two tests to make are continuity tests
of the line cord as shown at positions 1 and How to Replace Heater
2. The line cord should show near zero resis- Parts
tance from each of the prongs on the plug
to the terminal of the switch and the neutral After you have located the faulty part, replace
side of the heater element. it with a new one. Do not try to repair it.
When making replacements on any kind
The switch should be tested next. With of appliance, it’s always best to use exact
the switch in the OFF position, you should duplicates of parts if you can get them. There’s
read infinity ohms across it. With the switch a simple reason for this: The duplicate part
turned to the ON position, you should read will mount exactly like the old one, without
near zero ohms. Any reading above one ohm trouble. Switches, for instance, are often
mounted by two ears or brackets held by
small screws or bolts and nuts. If the new
switch were a little larger than the old one,
3 you’d have to drill a new mounting hole in
SWITCH
the case. This would leave the original hole
exposed and make a sloppy-looking job.
1
HEATING Replacement line cords must be heavy enough
4
ELEMENT to carry the heater current. Replacement
2 switches must have a current rating at least
LINE CORD as high as the original or they’ll burn up in a
little while. Heating elements should always
have the same wattage as the original.
FIGURE 21—These are the points at which you
can make resistance or continuity tests on the
heaters.


When you are going to replace a coiled or a Check the whole heater again very carefully.
ribbon heating element, leave the old one in All connections should be tight and the ele-
place until you have obtained the new one ments properly mounted. Be critical of your
and are ready to do the job. By doing this, own work. It is much better for you to find
you can see exactly how the original element a small mistake than to have the customer
is mounted and how it is wound around the find it. The skilled professional technician
insulators and racks. If you should have to is never certain that an appliance will work
take the old one out, make a rough sketch until he turns it on and sees it work.
of how it was mounted on the insulators.
This will save you time if several days elapse The most important test is the safety check.
between the time you take it out and the time This test makes sure that there are no short
you put in the replacement. circuits, or grounds, between the electrical
parts and the case. These could cause a very
To replace a coiled element, be sure that it dangerous shock hazard to the users. The
isn’t stretched too much while putting it in first test for ground should be made with
place. If it is, it will be loose on the insulators a meter set for high resistance, between the
and could fall off and cause a short to the line-cord prongs and the case, with the switch
case. First fasten one end to the terminal, then turned on. This should read an open circuit
very carefully thread it around the insulators on a digital VOM, or no deflection at all on
until you get to the other terminal. Ordinarily the ohm scale of an analog VOM. Review
it will be a little short because the coil hasn’t the rules given in previous lessons for how
been stretched. Stretch it very gently until to make continuity tests and leakage tests
the open end just reaches the other line with various test equipment.
terminal. You may have to stretch it slightly
in the middle to get enough slack. Try to You should never hesitate to make duplicate
distribute the tension over the whole element; tests or to make the same test in several
it will last longer. different ways. For another test for grounds,
connect one lead from the meter set to AC
When replacing the flat-wire, or ribbon, volts to a good ground, such as a water pipe.
elements, each turn of the element should Now, plug the appliance in and turn it on.
fall into a notch or hook on the mounting Touch a bare metal part of the case with the
insulators. Check the path and location of other lead from the meter, as shown Figure 22.
the original element very carefully before If you measure no voltage, the appliance
you take it off. Don’t let the ribbon elements is safe.
twist; this puts an excessive strain on them
when heated and can cause early failure.
Later on, you will study about other types
of heating elements such as those used on HEATER DIGITAL VOM
water heaters and electric ranges. We’ll
describe in detail the mounting of each type
of element as we come to it.
OUTLET

Testing after Repairs Are WATER
LINE CORD BARE PIPE
Finished METAL
PART
Now we come to a very important part of
the job: testing to be absolutely sure that FIGURE 22—This diagram shows how to perform a
the appliance will work just as it did when leakage test on the case of a heater or other
it was new, and that it will be safe to use. metal-cased appliance.


Reassembling the Heater If you can’t find an exact duplicate screw
and the missing screw is visible from the
After all the tests have been completed, front, look underneath or on the back. Take
put the heater back together. Be sure that out an original screw from there, replace
all screws are replaced. That’s why you it with another type, and put the original
put them all in the same box, to keep them screw where it can be seen. This makes the
together. Quite often, appliances will come job look neat. Careful attention to little details
with screws missing. Replace the missing like this will help you build up a reputation
screws with new ones from your stock. The as a really skilled craftsman. Don’t ever over-
appliance will then be returned to the owner look details.
as good as new. Match the original screws
as closely as possible. In most cases, this
won’t be hard to do.


✔
Check It Out! 2
1. How does a thermostat control heat?

_________________________________________________________________________
2. Why does a thermostat use a bimetal blade?

_________________________________________________________________________
3. What is the probable trouble if the heater does not heat up when plugged into an
outlet with the switch closed?

_________________________________________________________________________
4. If a heater is designed to carry a normal current of 10 amp, what should be the
minimum current-carrying capacity (ampacity) of the line cord?

_________________________________________________________________________
5. What kinds of insulators are used for mounting heating elements?

_________________________________________________________________________
6. How should the connections of a heating element be made?

_________________________________________________________________________
7. Why should you slightly stretch the heating coil when mounting it?

_________________________________________________________________________
8. What check should you make after the heater has been repaired?

_________________________________________________________________________

9. How is the check for grounds made?

_________________________________________________________________________
Check your answers with those on pages 81–82.


COMBINATION OF Resistance of Heating
HEATING ELEMENTS Elements
When you know the current drawn by the
heating element from an AC line, you can
Current in Heating Elements determine the resistance by the formula of
Ohm’s law:
The amount of heat produced in a device is
measured in calories or British thermal units R = E/I
(Btu), but we seldom need to know how
many calories are produced by a toaster, an in which
electric range, or any other electric heating R = resistance, in ohms
appliance. We are mainly interested in finding
at what rate the heat is produced electrically. E = line voltage, in volts
This rate is measured in watts. The rate of
heat depends on the power that the appliance I = current, in amperes
draws from the electric circuit to produce a For most small home appliances and lamps,
desired amount of heat. Therefore, heating the line voltage is 120 volts, but water heaters,
appliances are rated in watts or kilowatts ranges, dryers, and other heavy equipment
(1 kilowatt, or 1 kw, = 1000 watts). require 240 volts.
Usually the wattage rating of a heating For example, a 3000-watt heater which draws
appliance is indicated on the nameplate. 25 amp from the 120-volt line has a resistance
Since the voltage is generally 120 volts, the
current drawn by the appliance can be R = E/I
determined by dividing watts by volts.
The formula is = 120/25 = 4.8 ohms

I = P/E What will happen to the wattage produced
by the heater if the resistance of the heater
in which is increased? Let’s assume that the 4.8 ohm
heating element is replaced by an element
I = current, in amperes
which has a 10-ohm resistance. First, find how
P = power, in watts much current the new element will draw from
the line. You can do that by applying another
E = voltage, in volts form of Ohm’s law, which is
For example, you may want to find the I = E/R
maximum current a 3000-watt heater will
draw so that you can use the right size of In other words, divide the voltage by the
fuse or circuit breaker in the heater circuit. resistance to get the amperes:
Fuses and circuit breakers are rated in current
I = E/R
values, such as 20 amp or 30 amp. For the
3000-watt heater the current will be = 120/10 = 12 amp.
I = P/E The 10-ohm element draws much less current
than the 4.8 ohm element. Remember the
= 3000/120 = 25 amp.
rule: More resistance draws less current at the
You should select a 30-amp fuse or circuit same line voltage.
breaker.


Now you can find the wattage by multiplying
voltage and current. The formula is

P=E×I 120 VOLTS 400
WATTS
= 120 × 12 = 1440 watts
TOTAL POWER = 400 WATTS
This wattage is much lower than the wattage
(a)
obtained with the 4.8-ohm element. So, the
rule is: More resistance draws less power at the
same line voltage. 400 400
120 VOLTS
WATTS WATTS
Now let’s assume that the 4.8-ohm heating
element has been replaced by a 2-ohm
TOTAL POWER = 800 WATTS
element. The current drawn from the line
(b)
will be

I = E/R
120 VOLTS 400 400 400
= 120/2 = 60 amp WATTS WATTS WATTS

and the power will be TOTAL POWER = 1200 WATTS
P=E×I (c)

= 120 × 60 = 7200 watts
FIGURE 23—This illustration shows how more heat
Lower resistance causes higher current and can be developed using parallel heaters.
higher power at the same line voltage.
parallel with the first two, as in 23(c), we get
The foregoing rules will be helpful when three times the power of one element, or
replacing and combining heating elements. 1200 watts.

How can we make a variable heater using
Multiple-Heat Circuits with these three elements? By using a selector switch
Parallel Elements which will connect one, two, or three elements
across the circuit, so that 400, 800, or 1200
Let’s see how heating elements can be used watts can be produced by the combination
to get different heat outputs. Assume that of elements. As shown in Figure 24, one end
we have three heating elements, each one of each element is connected to the common
rated 400 watts. This information is on the side of the AC line. The other side of the line
tag or the label on the heater. The elements is connected to a selector switch, which is
are made for use on a 120 VAC line, and here of the shorting type. The movable bar
therefore, if connected across 120 volts, each is connected to the hot side of the AC line.
one will develop heat at a rate of 400 watts. The bar can be moved from left to right to
make a connection between the powerline
If we connect only one of the elements
and one, two, or all three of the elements. The
across the 120-volt line, as in Figure 23(a),
switch is shown in the MEDIUM position.
we get 400 watts. If we connect another
Two of the elements are connected, while the
element in parallel with the first, as shown
third is still open; thus 800 watts is produced.
in 23(b), we have the same voltage across
By moving the shorting bar one position to
each one and we get double the power, or
the left, or to the LOW position, we would
800 watts. Connecting the third element in
have only one element connected in the


If you turn the switch to the LOW position,
HOT WIRE
all three elements are in series in the circuit
LOW MEDIUM supplied by the line voltage. The current
400 800 HIGH
drops to one-third of its original value, and
WATTS WATTS 1200
120 VOLTS WATTS the wattage drops to one-third of the value
of one element, or 400/3 = 133 watts. If you
COMMON 400 400 400
WATTS WATTS WATTS want to measure the voltage drops, you’ll
WIRE
find one-third of 120 volts, or 40 volts, across
the terminals of each element. This equal
SHORTING division of voltage and wattage works out
SELECTOR SWITCH
only if each element has exactly the same
FIGURE 24—Multiple heat settings can be accom- resistance.
plished using a switch to select parallel heating
elements. In appliances themselves you will find
elements of different wattages used in
circuit, producing 400 watts. By moving multiple-heat circuits. The actual wattage
the bar all the way to the right, or to the depends on the work the appliance is sup-
HIGH position, 1200 watts is produced. posed to do, and how much heat is needed
in each position of the selector switch. The
manufacturer can combine resistance values
Series-Connected Elements so that they produce exactly 100, 200, and
300 watts on the three positions, or any other
Now let’s connect two equally rated elements groups of selected wattages.
in series. How much wattage will two 400-
watt elements develop when connected Always remember the following basic
in series? Each one of them has a certain principle: The lower the resistance of the
resistance R. When we connect two equal heating element, the higher the wattage at
resistances in series, we double the resistance the same voltage. In a series combination,
and the current will be cut in half. The voltage as in Figure 25, the single element has the
remains the same. If the current is cut in half, lowest resistance, but will be the hottest
the wattage also is cut in half. We would get one and will produce the highest wattage.
200 watts, or one-half of the value of either Let’s assume, for example, that in a coiled
one of the original elements. heating element of a room heater, a 10 cm
(4 in.) piece breaks off at one end. If you
If all three elements are connected in series,
as shown in Figure 25, a selector switch may
be added to change the element combina-
SELECTOR
tions. The switch is not of the shorting type. SWITCH
With the selector switch in the farthest left, LOW
or HIGH position, only one of the elements HIGH 133 WATTS
400 WATTS
is connected in the circuit. This would give MEDIUM
400 watts. Turning the switch to the middle 120 VOLTS 200 WATTS
position shown in Figure 25, or MEDIUM
position, the current has to go through both
elements connected in series. Since the resis- 400 WATTS 400 WATTS 400 WATTS
tance is double, the current is one-half of the
previous current and the heat is produced FIGURE 25—This illustration shows how series-
with a power of only 200 watts. connected elements may be selected for varying
heat output.


stretch the remaining part and connect it would be instantly melted because it would
again, the element will get considerably draw a very high current, develop a very
hotter, because you have taken out a part high wattage, and produce so much heat
of the resistance and made it possible for that the copper wire would melt.
more current to flow through the element.
A simple rule will help you to remember
Similarly, if you connected a short piece of this principle: The more wire, the less heat,
wire directly across the 120 VAC line, with- and vice versa.
out any fuses or circuit breakers, the wire


✔
Check It Out! 3
1. What current, in amperes, will flow through a 50-ohm heating element connected
to a 120-volt supply voltage?

_________________________________________________________________________
2. What is the wattage obtained from a 20-ohm heating element connected to a 120-
volt supply voltage?

_________________________________________________________________________
3. If a 500-watt heater operates at 120 volts, what is the current flowing through the
heater?

_________________________________________________________________________
4. If a 30-ohm heating element is replaced by a 60-ohm element, how will the wattage
change if the voltage remains 120 volts?

_________________________________________________________________________
5. What is the total wattage obtained from two 500-watt heating elements connected
a) in parallel? b) in series?

_________________________________________________________________________
Check your answers with those on page 82.

9304

Recomendados

Recomendados

Mais conteúdo relacionado

Mais procurados

Mais procurados (20)

Destaque

Destaque (20)

Semelhante a 9304

Semelhante a 9304 (20)

9304