Connect the Test-Set to the Relay – Alternate DC Connections


Connect the Test-Set to the Relay – Alternate DC Connections

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Life in the real world isn’t always perfect. This video demonstrates some alternate connections you can use to get around the most common obstacles when connecting  your DC connections between your test-set and the relay.


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Good morning Chris,

Just to clarify myself. You explain two different ways to sense the relay has operated.
1) The contact closed and that is it, a contact that was open and the protection make it, like it was tripping a breaker. It is a Open contact then the contact closes due to an over current, for example
2) This second will be sensing the voltage or it is sensing voltage across an open contact and, because contact closed no voltage across the contact?

Chris Werstiuk (Administrator) July 18, 2020 at 9:07 am

When you use a normal (dry) contact sensing connection where you connect the Test-Set Input across the Relay Output, the test set supplies its own signal from the positive terminal. If the relay output contact is open, the test-set signal has no path to the negative terminal, which means the test-set doesn’t sense its own signal; so it assumes that the contact is open. If the relay output contact is closed, there is a path for the test-set signal, which means that the test-set sends and receives the signal and assumes the contact is closed.

The test-set (dry) signal is low voltage and can be affected by interference or electronics in the relay output contact.

All test sets also have voltage sensing (contacts) that use external voltages to detect the relay output contact. When voltage sensing is selected, the test-set input terminals become an over-voltage relay. Some test-sets allow you to choose the voltage set-point, but most don’t. The test-set will assume that the contact is open when the measured voltage across the input terminals is less than the over-voltage setpoint. If the measured voltage across the measured terminals is greater than the setpoint, then the test set will assume the contact is closed.

The connections in video show you how to connect the test-set to the relay so that no voltage is applied to the input terminals when the relay output contact is open, and full voltage is applied across the test-set input terminals when the contact is closed.

Thanks Chris, really valuable tips indeed.

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