# How do you test a relay using a meter?



## HMF (Mar 13, 2011)

If you suspect a relay is shot, how would you test it using a meter to determine this?


(Photos would be grest, if possible!)


Thanks,


Nelson


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## Tony Wells (Mar 13, 2011)

A relay consists of 2 major components: Primary Contacts, and an electromagnet. Basic function is to control the contacts by energizing the electromagnet. After identifying the terminals, check for continuity on the electromagnet coil. There can be some resistance, but should show continuity. The contacts may be NO or NC (Normally Open, or Normally Closed). Use an ohmmeter to verify that they are as marked. At this point, extremely low resistance is needed. Virtually zero. To test the functionality of the relay, the operating voltage for the coil must be determined. Applying operating voltage to the coil while measuring resistance or continuity of the contacts will test the switching function. NO switches should close, and NC should open. Some relays will have capacitors across the contacts to reduce arcing, but not all. If the capacitor has failed, the open resistance will be high, in all likelihood. Visually check for burns and pitting of the contacts. Often, high resistance across the contacts will indicate carbon and pitting from arcing.

Sorry, no pictures available at this time. These are just the basic tests for a common relay. There are options That can add to this test procedure. Auxiliary contacts and heaters come to mind.


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## Tony Wells (Mar 16, 2011)

Oh, I dunno TD. It needs some editing. I'll try to get it done today.


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