Isolate the Relay From the System


Isolate the Relay From the System

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Watch this video to see how to properly isolate a relay from the system and follow the correct order to prevent mis-ops. Isolating the relay from the system in the wrong order can be pretty embarrassing when things trip and alarm when they aren’t supposed to. ¬†Ask me how I know!


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Can you explain why you opened the voltage test switches before the currents?

Chris Werstiuk (Administrator) March 12, 2019 at 6:56 pm

Good question! No reason. Once the trips are isolated, you can open any test switch in any order.

Hi Chris,
I understood isolating the relay for testing.
My concern is that once you tested a function, overcurrent for example, this relay will not see that the breaker tripped because we open the test switch. Is that right?

Chris Werstiuk (Administrator) July 11, 2020 at 10:04 am

You are correct, but you may be conflating two different tests. When performing relay testing, you will be sending many trip signals to the circuit breaker, so most relay testers will isolate the relay from the circuit breaker. This is mandatory when performing relay testing when the circuit breaker is closed, which should only be performed when there is primary and backup protection is installed and you only test one at a time. There is no reason to isolate if the circuit breaker is already open or the lockout relay is already rolled.

A functional test is trying to prove that the wiring between devices is OK and that the circuit breaker trip coil will receive the trip signal when it is sent. Many people perform this test by applying a jumper across the contact, but this is the worst case scenario. One of the failure points inside a digital relay is that the output relay connected to those terminals. The relay could send a trip signal to the output relay, but the output relay can;t mechanically open or close. Therefore, pulsing the output is a better way to perform a functional test because it also tests one of the failure points inside the relay.

The perfect functional test would be performed as you suggest. You keep the test-set voltage and current signals connected to the relay, close the DC test switches, close the circuit breaker, and then run one of your timing tests. The circuit breaker should open and you should be able to look at the relay to see if it saw the circuit breaker closed and opened.

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