How to test a relay

This article shows you how to test a relay. A relay will usually have a coil, pole terminal and a set of contacts. The set of contacts that are open when the relay is not energized are called normally open (N/O) contacts and the set of contacts that are closed when the relay is not energized are called normally closed (N/C) contacts. The following steps can be used to perform the testing of the relay using a multimeter.

  • Keep the multimeter in the continuity check mode.
  • Check for continuity between the N/C contacts and pole.
  • Check for discontinuity between N/O contacts and the pole.
  • Now energise the relay using the rated voltage. For example use a 9V battery for energising a 9V relay. The relay will engage with clicking sound.
  • Now check for continuity between N/O contacts and pole.
  • Also check for discontinuity between N/C contacts and pole.
  • As a final test, measure the resistance of the relay coil using a multimeter and check whether it is matching to the value stated by the manufacturer.

If all the above tests are positive we can conclude that the relay is healthy.



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11 thoughts on “How to test a relay

    • Seetharaman

      Hi use a multimeter in its diode continuity range. one way it should indicate 550 to 700mV and other way by inter changing the probe connecting to diode should show over range. If it is showing less in both ways then it is defective.

  1. Gurjit Singh

    Hello i am confuse in some point as i know that dc voltage is not given to coil because x=2pie*f*L and
    in dc f=0 so reactance is zero and current go to infinite

    then why we apply dc voltage to the relay and how dc can produce the magnetic field in the relay because

    in dc there is no variation and inductor pass it without any effect and

    no magnetic field produce when we apply dc to any inductor..?

    please give me the answer of that question so that i can come out of my confusion.

    • tilahun temechew

      it is known that any current caring conductor can create magnetic field around the wire so, dc current can create magnetic field. As you say no time varying current in dc source but magnetic field can be created even with dc current. you have to know that alternating current is mandatory to create an EMF (ELECTROMOTIVE FORCE).


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