I have a 220v pump that has two terminals. They are connected to the circuit breaker with both hots, the neutral isn't connected to anything on the pump.

I'm trying to hook up a controller (relay) for a thermostat. I thought I knew how to hook it up, but it didn't work out so well (I fried the transformer in the relay box, which I don't really understand since it's rated for 220v).

I think the pump controller needs to be connected to the neutral with one hot connected directly to the pump, and the other side being switched by the relay.

Is that right? I'm hoping to avoid more smoke!

This is what I'm thinking of doing

  • This controller is for a gas valve very tiny load or every millivolt relay I have worked with was. Read Harper's post and do that you will save a bunch and be much safer.+
    – Ed Beal
    Commented Oct 31, 2017 at 23:30

2 Answers 2


On your wiring diagram, what is the blue wire connected to in the breaker box? Remember, the relay may be rated for 230 volts but the power to the relay terminals 1 & 2 are 120 volts. Also what is the amperage of the pump and it's horse power? I would prefer using a Honeywell R845A-1030 DPST relay to switch both power legs to the pump so that no power was being sent to the pump when it not supposed to be running; (makes for a safer pump). The starting amperage of the pump is many times the running amperage. Hope this helps.

  • The blue line is connecting to the neutral in the breaker box. I did it that way just to make it easier to see compared to white. I'm looking at the R845, thanks!
    – kevin42
    Commented Oct 31, 2017 at 12:54

Ok, hold on. Are you sure you followed the instructions? Is your model number the same one in the instructions? Reason I ask is, having to bring out neutral just for this is stupid. That transformer inside the relay ought to be 240V.

So I think you got a defective one, or at least the wrong one.

Normally thermostat circuits are 24V, though this transformer may be doing something a bit different - I'd consult the factory.

The more standard way to do this is a 40VA 24V junction box mounted transformer (for about $11) which can mount anywhere, common thermostat cabling, and then a common air conditioning relay (about $13) inside a large junction box ($9). This has several advantages: it will switch both poles, so when the equipment is off, it's really de-energized. It operates on standard thermostat voltage, so you can use more readily available standard controls. And if you have a furnace with surplus 24V power, you can just poach power off that instead of using your own transformer. Also it's made to switch inductive loads, which is not necessarily true for relays like this.

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