3 phase compressor DOL wiring

Fall-Apart-Dave · Aug 5, 2021

Hello. I bought an old three phase compressor but it has come without a starter switch. Just five cables, two for the pressure switch and three for the three phases.

I have a DOL starter switch, but I don't know how to wire it to make the compressor come on and off with the pressure switch. Obviously my phases gonon T1, T2 and T3. But the pressure switch, where would that go to make the compressor automatically start and stop as it goes open and closed circuit? I have a wiring diagram I was supplied with but wanted to ask real professionals before jumping in.

Thanks in advance

[ElectriciansForums.net] 3 phase compressor DOL wiring

Julie. · Aug 5, 2021

Remove the existing red wires, then wire it exactly as the diagram, it will start and stop according to the pressure.

The start/stop on the starter will no longer work, so you must add an isolator rated for the full motor rating ahead of the starter to isolate it.

There are ways to add an emergency stop button, but to do it properly you need a second contactor so it locks out.

Fall-Apart-Dave · Aug 5, 2021

Thanks for that. Very much appreciated. A1 and A2 in the diagram, what do they correspond to?

Julie. · Aug 5, 2021

Fall-Apart-Dave said:
Thanks for that. Very much appreciated. A1 and A2 in the diagram, what do they correspond to?

A1 and A2 on the starter.

I think L1 is already connected into A1 or A2 at the moment via the red wire

Fall-Apart-Dave · Aug 5, 2021

Just here? Unlabelled terminals at the bottom?

Really appreciate the help. I'm glad I didn't jump in, I'd assumed the pressure switch went between 96 and 14.

Thanks again. I have an isolator switch, an EM stop will be fitted too.

Shame it can't be made to work with both the buttons and the pressure switch. Oh well!

Julie. · Aug 5, 2021

Fall-Apart-Dave said:
Just here? Unlabelled terminals at the bottom?

Really appreciate the help. I'm glad I didn't jump in, I'd assumed the pressure switch went between 96 and 14.

Thanks again. I have an isolator switch, an EM stop will be fitted too.

Shame it can't be made to work with both the buttons and the pressure switch. Oh well!

View attachment 88323

Yes, I imagine they are marked somewhere

netblindpaul · Aug 5, 2021

You can have a pressure switch, e-stop and buttons, or a combination unit, it’s just the one that you have is not suitable for use in that manner.

Fall-Apart-Dave · Aug 5, 2021

Best I get googling!

Lucien Nunes · Aug 5, 2021

The point being that the contactor either has to latch the state of the buttons (i.e. whether the start or stop button was the most recently pressed) or follow the position of the pressure switch. One contactor can't do both.

If the unit requires an unloading valve and the valve is built into the pressure switch, and the pressure switch has a manual control, then you should preferably start and stop the unit with the pressure switch manual control. Otherwise if you stop the motor using a separate manual switch or button while running, the unloading valve won't operate and depending on how good the N/R valves are it might take a while before it can be restarted without stalling the motor.

Fall-Apart-Dave · Aug 5, 2021

Understood. There is no switch at all, or unloader valve. It's just 3 wires to the motor and two to the switch.

3 phase compressor DOL wiring

Fall-Apart-Dave

Julie.

Fall-Apart-Dave

Julie.

Fall-Apart-Dave

Julie.

netblindpaul

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Fall-Apart-Dave

Lucien Nunes

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Fall-Apart-Dave

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