Heater Element; Resistance Measurements; Insulation Resistance Measurements; Voltage Measurements - Cleveland steamcraft 21-CET-8 Service Manual

Page 80 Model 21-CET-8 Service Manual

Heater Element

Resistance Measurements

Insulation Resistance Measurements

In this text, heater element refers to the complete assembly. The heater element
contains three coils. Wire markings identify each coil as follows:
• Coil 1 connects to leads 1L1 and 1L2
• Coil 2 connects to leads 2L1 and 2L2
• Coil 3 connects to leads 3L1 and 3L2
Deenergize all circuits before connecting any resistance measuring device
such as an ohmmeter. Notice that the ON/OFF switch set to OFF does not
remove power from all 120 VAC circuits. Remove both 2-amp fuses, or turn
power OFF at the main power switch. Measuring resistance with power
applied may damage your meter.
Before measuring resistance of any component, isolate the component by
disconnecting one or both circuit leads from the component. This win
prevent a false reading caused by circuit paths through other components in
parallel with the one being measured. Remember to replace the component
leads after making the measurement. Figure 5-10 shows a typical ohmmeter
connection.
When measuring the insulation resistance of heater coils to ground use a 500 or
1000 volt megohm meter (megger), if available. Ordinary multimeters do not
always detect insulation breakdown because they use low voltage batteries to
supply power for resistance measurements True insulation resistance
requires a high voltage megger reading. Multimeters can be used only to
make a quick check for gross insulation breakdowns. Set the multimeter to
the higher scale and then zero the meter using the zero adjust. An insulation
resistance of less than one megohm usually indicates poor insulation. A very
low resistance (less than 1,000 ohms) indicates broken insulation.
Voltage measurements require care. Always test your meter on a known
voltage source to ensure correct meter operation. Any 120 or 220 VAC outlet
provides a convenient voltage source. Circuits that appear dead because a
faulty meter indicated 0 volts have resulted in many hair raising (and deadly)
experiences for even seasoned troubleshooters.
When checking voltages, set your meter to the proper scale. For example, if
checking 120 VAC circuits, use a higher voltage meter scale such as 250 or
500 VAC. Use AC scales for AC circuits. DC meter scale readings on AC
circuits yield incorrect results.
If your voltmeter doesn't have the exact scale as stated in any component
test, use any convenient scale higher than the expected voltage. For
example, if the test calls for setting the meter on the 250 VAC scale for an
expected reading of 120 VAC, and your meter doesn't have a 250 VAC
scale, use the 500 VAC scale. Figure 5-11 shows a typical voltmeter
connection.
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