Current relay/potential relay

Checking PMRs and CMRs

Checking a Current Magnetic Relay:



Take a resistance reading across the coil on the relay (usually terminals L and M) - The resistance of the coil should be less than 1 ohm or so.



Position the CMR in its normal position (coil at the bottom) and check for continuity across the contacts of the relay (Terminals S and L). This reading should be infinite. Now, with the meter's leads still connected to S and L, turn the relay upside down. You should now read continuity. This indicates that the contacts are moving freely within the relay.



If the coil and the contacts check out, the relay is good.



Checking a Potential Magnetic Relay:



Take a resistance reading across the coil (terminals 2 and 5) on the relay - The resistance of the coil should be very high. This resistance varies from manufacturer to manufacturer, but readings well above 1000 ohms are common.



Next, check for continuity across the contacts of the relay (Terminals 1 and 2). This reading should be zero or very close to zero.



If the coil and the contacts check out okay, there is still the possibility that the relay is not functioning properly. You still need to check whether or not the contacts open when the "pick-up" voltage is reached. The pick-up voltage is the voltage at which the contacts will open, and is much higher than the line voltage that is supplied to the unit.





I hope this helps!