Maker Pro
Maker Pro

Home Wiring: 230 VAC 1ph motor Question?



Jan 1, 1970
The building I live has in the past only been wired for 120VAC is a WWII era building and had weak electric service. A
couple years ago the owner did an electrical upgrade and installed a
breaker panel (previosuly there was just a fuse box with screw in
fuses) in my apartment and promised 220VAC service. Before the work
was completed, the owner ran afoul with an asbestos issue in the
basement and the second phase of the electrical service was never
connected by the electrical utility. So, we've only had 120VAC
I want to hard wire a compressor that has a 230VAC single phase motor,
drawing 22 FLA. Recently, I checked my service box and finally I now
have 220VAC service.
My question regards the circuit's grounding and connection to the

We have BX metal cable in this building which is the local NYC code.
The breaker panel has metal Greenfield conduit connecting to it with
three wires entering the panel: white/red/blk. There is no green
ground wire.
Red connects to one side of the breaker terminal. Black connects to
the other side of the breaker terminal. White goes to a seperate
terminal, and I am assuming the white is thus neutral.

Here are the meter readings I get when testing at the breaker panel:
Blk/Red =209VAC
Blk/Wht =120VAC
Red/Wht =120VAC
Wht/Service Panel = 0.29 VAC
Blk/ Service Panel = 120VAC
Red/ Service Panel = 120VAC


I will run BX cable from the service panel to an enclosed metal
switchbox: and then from the switchbox to the motor. I am using
10guage wire for the circuit.

1) I need either a Duplex Breaker, or 2 Single Breakers to control the
circuit. What should each pole of the breaker be rated at? Is 30amps
2)Will a 230VAC single phase motor run OK on 210VAC service?
3)The motor has 2 wires and a ground wire. From my understanding I can
run the Red (120VAC) & Blk (120VAC) from the breaker panel to the
switchbox, and then from the switchbox onto the motor. However, what
do I use as a ground wire???
If I put a copper grounding screw into the service panel and run a
green ground wire off of that, it seems tat, hypothetically, if I get
a short (ex., Blk goes to my green wire grounded to the service
panel) it will conduct 120VAC.
Am I missing something here?

I have the current NEC codebook but am still perplexed.
Thanks for any clarification.

Rich Grise

Jan 1, 1970
1. Use a duplex breaker - if one side faults, you want to
turn both sides off.
2. Yes - these are "nominal" voltages - and if you've really
got 2x 120, that's 240. :)
3. The two motor wires are probably for black and red - don't
even bother running a neutral, and ground it to the conduit/
box. The neutral is grounded somewhere near the entrance panel;
if you short one phase to ground, it _SHOULD_ pop the breaker;
you could also look into a GFI Ground Fault Interruptor.

Good Luck!