Troubleshooting for a Phase Reversal (Phase Sequence) Problem

Alternating Relays


I have purchased one of your three phase monitor relays and have connected it per the diagram on the unit. However, I cannot get the unit to operate–it just won’t turn on. What’s wrong?


Most problems when first installing and applying a three-phase monitor relay are due to phase sequence issues. Although you may have connected Phases A, B & C per the diagram on the product, this does not necessarily mean your three phases are in the same sequence as what the relay is looking for. The first thing to try when a three-phase monitor does not work on power up is to switch two of the three wires connected to the unit.

Troubleshooting: Macromatic Phase Monitor Relay wiring diagram

After all, there are only two true phase sequence possibilities, so if the initial set-up of A-B-C does not work, all you have to do is switch the wires coming to the A & B terminals on the unit (see diagram above). That should solve the problem. Remember: it is not required that the phase designation of your system match the connections to the three-phase monitor relay, i.e., Phase A from your system to terminal A, Phase B to terminal B, etc.; the connections from your system must be in the same sequence as what the unit is set up to use as the basis for offering phase reversal, or sequence, protection.

As always, if you have any problems with selecting, installing or applying any Macromatic three-phase monitor relay, please contact us for help.