I have a 3 phase well pump that I would like to wire up a 120 volt indicator lamp that if any one of the 3 phases that feed the pumps shut down then my lamp will then shut off so I can tell from a distance that I have a problem when my lamp is no longer lit.
How would I wire this concept up?

1 Answer 1


Use a motor protection switch or a phase loss relay.

Every manufacturer has one, for instance this one from RS. I'm not affiliated with RS; it's simply the first one in a search.

Use the relay output to switch off the pump and give a warning that you have phase loss.

In addition, a motor protection switch will trip on imbalance between the phases. This is not as quick or good protection as a phase monitoring relay, but will generally trip before the motor is damaged if properly adjusted.

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