Basic Electrical Troubleshooting

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Key Questions

The following key questions are answered in this module:

What is a multimeter?
A digital multimeter is a single instrument that is capable of measuring voltage, current, and resistance. It is very useful for troubleshooting electrical circuits and equipment.

Define voltage measurement.
Voltage is a measure of the charge potential between any two points in an electrical circuit. The measurement can be made by simply contacting the probes of the meter to the appropriate points in the circuit. Voltage readings can be relative or absolute. Absolute readings are those which are measured against a reference, or ground point. Relative measurements, or voltage drops, are those which are made between any two arbitrary points in a circuit.

What is the purpose of a clamp ammeter?
A clamp style ammeter can measure currents of several hundred amps and detect current flow without being directly connected into a circuit. This type of ammeter has a set of split jaws which can be opened and then closed to surround a wire. Clamp meters are not as accurate as in-circuit meters, particularly at lower currents, but for troubleshooting purposes, they are much safer and more convenient.

What is a megohmmeter?
A megohmmeter (or megger) is a type of resistance tester that measures much higher values of resistance than a multimeter. It measures into the millions of ohms, hence the prefix and name, "meg"- ohmmeter.

What is the purpose of a transformer?
Transformers are used to increase or decrease the value of alternating current voltage.

Sample Video Transcript

Below is a transcript of the video sample provided for this module:

Three phase transformers have electrical similarities to three phase motors and can be troubleshot in a similar fashion. They share the characteristic that one leg or winding can be bad, but that the overall device can appear to be functioning correctly. If one leg of a transformer is not conducting current, the transformer will overheat, as does a motor with the same condition. Just as with a motor, all of the phases of a transformer should have a very similar voltage with respect to ground and should show a similar current flow when measured with a clamp ammeter. Isolating a power transformer is a little more difficult than isolating a motor, but once it is offline, continuity and resistance tests can be run on the phases as described for testing motor windings.