Testing the Contactor/When to Replace It

Voltage drop test1

 

If you are in doubt about the condition of the contacts of a contactor, a simple test with a voltmeter will provide you with enough evidence to help you decide whether to keep the contactor or replace it. The 20-V reading in this figure is excessive. The maximum voltage drop across the contacts should be no more than 3% of the rated line voltage. If this is calculated for a 208-V system, the maximum voltage drop should be no more than about 6 V (0.03 208 V = 6.24 V). Thus, a voltage drop of 20 V tells you that the contactor must be replaced.

EXCERPT FROM ELECTRICITY FOR HVACR TECHNICIANS available from the online store at RSES (Refrigeration Service Engineers Society) The HVACR Training Authority

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