contactors and controlling single110 and 220v 3 phase power...

crossposted from general

Hey guys, I'm involved in a 5 axis cnc router build and we're working on electronics now while we wait for parts. We need some major help with something that in theory should be simple, but until you do it...

We're using the pmdx series of breakout boards, and we're using geckodrive stepper drivers powered by a 56vDC psu (110vAC) and a 220v 3phase spindle

I've been looking at this drawing all day(the normally closed Estop one), from what understand the estop and relay on the board engage the contactor which cuts power to the stepper motor psu.

But in our case how would we integrate a 220v 3phase contactor into this schematic? Whats the safest way to do this? Using another relay or could both contactors be run together? Do we need two contactors?

I've been researching all day but I'm missing something, I would really appreciate any help or even a quick schematic to look at would be great!

thanks guys!

Please don't cross-post.

I've worked with 3 phase 440vac contactors (sometimes called motor-starters). You can think of them as large 3 pole single throw relays. The relay coil (often called the M coil) wires to some signal phase AC control voltage, often 120vac but sometimes 24vac. That is about all I will say on the subject, as the common adage around here is "if you have to ask you probably shouldn't be messing with it". If that is the case you would be better of getting assistance from someone qualified in such equipment, as the voltage and power levels can be very dangerous.


What is shown in your schematic is a single phase contactor. A 3 phase contactor would have 3 wires in from the mains and 3 wires to your spindle motor. But as Retrolefty points out, it would be a good idea to play it safe and seek a qualified electrician to take care of the wiring. Also, I might point out that these sort of questions would be more appropriate to ask on the forums at where you will find a lot of people who are very experienced in this sort of thing. Good luck with your project!

sorry for the cross post,

thanks for the replies guys, I will definitely want an electrician or controls specialist to check out my wiring later but for now I’d like to be as knowledgable as possible.

I was given the advice from two separate knowledgable sources to either run a 4 pole contactor and switch the 3 phases of the 220 and the hot leg of the AC, or to use two contactors, a 2 pole (for 110 single phase) and 3 pole contactor (for 220v 3 phase) wired in parallel. Both of these would be 110 coil voltage contactors.

Is one of these better than the other concerning safety?

I was given the advice from two separate knowledgable sources to either run a 4 pole contactor and switch the 3 phases of the 220 and the hot leg of the AC,

I like this first option better, mostly because fewer parts = better reliability and there would less likely be a failure mode where you have one contactor power on and one power off due to mechanical or electrical failure.

If you must use two separate contactors, wire the output 120vac from the 120v contactor to control the 220 volt contactor. This would result in a 'interlock' feature where the 220v contactor could not activate unless the 120v contactor was also activated.


Hey guys thanks for the replies again, these are great comments and I've now decided that these safety circuits and power considerations are best left to an outside consultant or engineer.


I wanted to know any thoughts on the ramifications of using one circuit or two? i.e.

separate 3 phase 220 and single phase 110, OR pulling the 110 off of the 220 line. Is one a best practice concerning safety? Are there noise/interference ramifications?

OR pulling the 110 off of the 220 line.

Where would the 110 neutral wire come from on the 3 phase 220 feed, a seperate wire from the service box? If you have to run an additional wire I would just have a complete 120vac circuit run from the service box and leave the 220 in it's own circuit.

Again best to let a local experianced expert (in both NEC and local building codes) help you design the installation.