Home CNC Router Electrical Question

I’m putting a CNC router in at home. It is in my detached garage. I need to run some wire and install outlet(s) for it and have some questions…

The spindle, driven by a VFD, needs 220V service and draws something like 9-10 Amps.

The rest of the electronics use 110V service and current consumption is pretty low. This includes the computer, the control board for the motors and spindle, the stepper drivers, etc.

I have plenty of 110V outlets in the vicinity but need to run the 220V.

I happen to have a spool of 12/2 Romex already. With this I could run a 220V 20A outlet, plenty for the VFD+spindle, but I would not be able to split off a 110V outlet for the electronics. This would mean the spindle and the controlling electronics would have different paths to ground (on different branch circuits) but would also be connected via low voltage signal grounds.

As much as I play with electronics, things like ground loops still mystify me (because I’ve never cared or needed to).

Is this a potential problem? Should I pick up some 10 or 12/3 and run both the high and low voltage stuff off the same branch circuit?

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Keep the other electronics as isolated as possible from the VFD. You should be fine with your grounds. The VFD may put some noise back into the incoming power depending on how good the drive is. That can make your electronics go ape$hit if it puts noise back into the line. Ive seen a drive cause issues with other drives, of course the customer was blaming our equipment. If you start seeing noise I would suggest an input line reactor/filter. Make sure your ground comes back to a single source… Ie make sure your chassis ground goes to actual ground.


I’m no electrician, but assuming standard residential 2-phase power, 3-conductor wire should allow for 240V across the phases and 120V to neutral.

@ESmith So that’s sort of the crux of my question. I will be running a 220V outlet regardless. The question is whether to run 2 (which I have) or 3 conductor wire. The 2 conductor won’t allow me to split off a 110V outlet. The 3 conductor will, but at considerable expense (since I don’t have the wire).

Qualifier… not an electrician … am I wrong in thinking the code now requires a neutral on new installs?

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Hmmm, not sure but don’t know what use a neutral would be for a 220V circuit. It only uses two hot wires (plus ground). The third wire wouldn’t be connected to anything. The only reason to have a neutral on a 220V outlet is if the device plugged in also needs 110V internally.

A 220V outlet like the one I’m talking about has no place to put a third wire.

Edit to add: there could be a requirement that three-conductor (plus ground) wire be run even if the neutral wire isn’t connected. This would be to help prevent some jackwagon in the future from repurposing the uninsulated ground wire to use as a neutral in a 220+110 configuration. If so, not my problem.

I’m not 100%, but that may only apply to dedicated appliance circuits like dryers and ranges.

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If it were me, I’d be considering this a dedicated-circuit appliance, especially at the 220V level.

If I read the code correctly, the neutral is not required in a 240V circuit that contains exactly zero 120V devices. Where the neutral is now required is applications like a clothes dryer that has 240V heating and motor circuits and 120V timers and similar small devices. Prior to the change, these supposedly small internal 120V users used the ground wire as a substitute for the neutral and that became a frowned upon methodology.

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@bertberaht Basically what I said :slight_smile: Don’t use the ground as a neutral.

2-conductor plus ground is legit as a 220 volt circuit. That’s why Home Depot has bins and bins of 2-conductor 220V outlets.

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