ECN Forum Forums General Topics of the Trade General Discussion Area motor starter

Tried hooking in the pressure switch control at different points in the control circuit. Same issue as o.p.

This was a customer supplied push button starter. I normally don't use these types for air compressors, and thought there would be a simple way without extensive rewiring, or adding extra parts/contacts/switches to keep the push buttons functional.

As others above have noted, the off/auto switch is what we normally use and best.

If you need to keep your 2 buttons, the cheapest way that will work safely is to add 1, DPDT control relay.
1.) Wire "L" or "Hi" to N.C. "OFF" button to N.O. "ON" Button to relay coil to OLs to "N" or "Lo"
2.) Wire relay N.O. contact in parallel with the "ON" button. (Holding contact for the control ckt.)
3.) Wire "L" or "Hi" to other N.O. relay contact to P-switch with differential to contactor coil. (Normal compressor cycling when control circuit is active.
Add any E-stop switches to Line 1. Just about any starter assembly should have the volume to add a control relay. I can do the ladders up on CADD if you want.
Joe

I don't think you can do this with a 3 wire stop/start unless you add a relay.

A simple toggle switch in a handy box will do to switch the control circuit. It isn't a lot of money.

Here is the partial ladder with the rotary selector switch and indicator.
Joe

Option 2 partial ladder, using a control relay to keep existing buttons.
Joe