EXTECH MG500 [12/15] Notes on measuring the resistance of a contactor or circuit breaker

MG500-en-GB_v1.3 3/17

Transformer Testing

Transformer tests are performed with the transformer completely disconnected from the line

and the load. Note that the case ground should not be removed.

The five tests listed below will completely test a single-phase transformer. Note that at least 1

minute should be allowed between each test.

1. High voltage winding to low voltage

winding and ground

2. Low voltage winding to high voltage

winding and ground

3. High voltage winding to low voltage

winding (pictured at right)

4. High voltage winding to ground

5. Low voltage winding to ground

Notes on Measuring the Resistance of a Contactor or Circuit breaker

A Contactor or Circuit breaker must provide a low resistance path to electricity when closed but

should provide a high resistance when open. As they age, their characteristics may deteriorate

because of heavy use, operation in a dirty environment, or other factors.

Unusual Insulation Resistance Measurement Applications

o Special paint or varnish may be used as an insulator on transformers and other electrical

applications

o Insulating blankets, suits and gloves can also be tested

Connect the

GREEN lead here

Connect the

RED lead here