Pulling 120V off a rotary?

lazlo · Jul 5, 2009

I'm running a Harig Super 6x12 off a rotary phase converter, and I've had to replace the oil pump with a 115V Little Giant.
Is it safe to reference one of the "natural" legs to the ground coming from the rotary to get 120V?

The oil pump is 1.7A @ 115V, and it's a 5 HP rotary, but I know the NEC frowns on using the ground for a return path.

I think the "right" way to do this would be to pull the neutral from the 220V single phase through to the Harig plug, but that would require a 5 conductor pigtail and connector...

Torque1st · Jul 5, 2009

What about just using an extension cord from a wall outlet temporarily?

A 240:120 transformer can be used to preserve the 3-phase power operation.

peterh5322 · Jul 5, 2009

The correct way to obtain a local supply of 115 single-phase is to install a 230/460-to-115 control transformer, to connect the 230 side to the incoming real phases, to ground on side of the 115, thereby making a "separately derived system", and to plug your accessories into that source.

The primary must be connected to the real phases. Connecting to a real and the manufactured phase will cause problems in the long run.

Note: if the 115 single-phase is used only for control purposes, and not for convenience outlets, then creating a "separately derived system" may not be required.

jim rozen · Jul 5, 2009

I would respectfully suggest that even if only used for control voltages,
seconaries of transformers like that should *always* be 1) bonded and b)
fused for overcurrent.

Jim

lazlo · Jul 6, 2009

Thanks for all the responses guys! I was hoping to avoid the transformer, but it sounds like the safest thing is to isolate the 120V line.

I'm scrounging around on Ebay for a 150VA transformer...

lazlo · Jul 15, 2009

Guys: follow-up question: so I bought a 150VA control transformer. What is the Code-Correct way of mounting it? It's too big to fit in the base of the Harig.

Is it OK, to just mount it on the back of the surface grinder? Or are you supposed to have a NEMA enclosure for the control transformer?

My Harig Super 6x12 is from the 80's, and doesn't have the control transformer shown on the modern Harig schematics. Could anyone with a late-model Harig tell me where the transformer is located?

Thanks!

Robert

peterh5322 · Jul 15, 2009

"Or are you supposed to have a NEMA enclosure for the control transformer?"

A steel pull box (Hoffman, or equal) should be OK.

wippin' boy · Jul 16, 2009

yup.........

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Pulling 120V off a rotary?

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