GFCI for Motor

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metelectric

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I have a single phase 240 volt, 12 amp saw used to cut granite slabs. My power supply is a 120/240 Delta system. The saw features a water feed which aids the blade's cutting by cooling it and creating an abrasive slurry.
The manufacturere wants this GFCI protected. Without a neutral in the motor this cannot be properly done. I have tried to make a GFCI breaker operate this, but unsuccessfully so.
If this motor is NOT cord and plug connected, does it need GFCI protection?
If I needd to GFCI protect this, how can I do it?

Thanks.
 
Re: GFCI for Motor

There were two 240 volt GFCI breakers on the market last time I checked. Square D and ITE Siemens.

Ed
 
Re: GFCI for Motor

And Cutler Hammer. The problem is that without sensing a neutral on the load side (Saw Motor) the GFCI doesn't work. The ground wire is an equipment ground and should not be used. I am flumoxed!
 
Re: GFCI for Motor

And Cutler Hammer. The problem is that without sensing a neutral on the load side (Saw Motor) the GFCI doesn't work.
Click to expand...
GFCIs do not require a load neutral to work. There are two types of 2 pole 240 volt GFCIs. One is only suitable for 240 volt loads, the other can be used for both 240 and 120 volt loads off and the 120 volt loads share the neutral. In either case the GFCI circuit looks at the sum of the current on all of the load conductors (either 2 or 3 conducots) and as long as the sum of the currents is ~5mA or less everything is fine. When the sum exceeds this value the breaker trips.
Don
 
Re: GFCI for Motor

metelectric,
My power supply is a 120/240 Delta system.
Click to expand...
And, with respect to the saw:
I have tried to make a GFCI breaker operate this, but unsuccessfully so.
Click to expand...
The first question back to you concerns the neutral. Are you connecting the 2-pole GFCI breaker with one leg on the High Leg? I assume, since your question concerns the neutral, in part, that the GFCI breaker is 120/240 Volt, not straight 240 Volt. To positively eliminate the electronics of the detection & trigger circuit of the GFCI, remove the possibility of a phase angle to neutral issue by not connecting the breaker to the High Leg.

If you have tried the 120/240 Volt hookup and the GFCI still trips, then there is a ground fault. . .in the saw or the branch circuit.
 
Re: GFCI for Motor

I am not aware of any major manufacturer of 2 pole GFCI breakers that require a LOAD side neutral. By the same token I am not aware of any GFCI that does not require a LINE neutral. For successful operation the GFCI breaker must be across the two phases that share the grounded conductor, probably A and C but you never know, and the pigtail to the grounded conductor.
 
Re: GFCI for Motor

The only thing a neutral brings to the party is the ability to use that PTT button which will not work without a neutral.
 
Re: GFCI for Motor

The only thing a neutral brings to the party is the ability to use that PTT button which will not work without a neutral
Click to expand...
A load side neutral is not needed for the test button to work.
Don
 
Re: GFCI for Motor

You're correct Don. I should have clarified what I was referring to is the application where there has been no neutral even brought out to the panel that the "white pig tail" can be connected to. I've gotten a lot of calls from electricians where they ask if the GFCI will still work where they have just run 2 lines and a EGC to an enclosed GFCI breaker that supplies power to a 240v load such as a hot tub or spa that doesn't require 120v.
 
Re: GFCI for Motor

You know, metelectric said 240/120 delta which implys a delta with a lighting tap. The he said the motor was 12a but didn't say if it was 1ph or 3ph. Being 240v it appears to be assumed that it is 1ph which should be clarified. If the motor is 240v 3ph GF protection has to be reconsidered.
 
Re: GFCI for Motor

I should clarify a couple things.

1>This is a single phase motor.

2>I intended to use the high leg for one side of the 240 motor, as a GFCI should be monitoring amperage variance.

3>I connected the line side neutral to the pigtail off the GFCI and did not connect anything to the load "neutral" terminal. Still did not work, it buzzed and shut off.

4>I then moved to pick up phases A and C, bypassing the high leg and it still did not work.
It shut off on energizing.

5>I tried to buy a "pure" 240 volt breaker at two supply houses and was told that none exist. The two pole 240 GFCI breakers evidently are all labeled 120/240. The manufacturers I checked out were Siemens, Sq D and Cutler Hammer. I think these breakers are designed for hot tubs with lights or 110 controls.

Can a brand new motor have a ground fault in it? Good idea but...
I think not, it runs fine on a 2 pole standard breaker. I cut a slab with it, standing on a wet floor. I am still alive (arguably) though I am still stumped by this thing. Could it be that, I fry the breaker on the Delta High leg and then it simply won't work after that in another location on the loadcenter?

Well, I am into my third breaker now and may have to get another. If the code allows it, I would hard wire this thing onto a standard breaker. But the manufacturer has a beef with that.
I appreciate all the input, keep it coming and when I solve this I'll let you know.
 
Re: GFCI for Motor

metelectric,

Three breakers, eh? Have all three, at some point in the experimenting, been connected to the High Leg?
 
Re: GFCI for Motor

When you connected the breaker to the high leg you may have "burned" up the electronics.

There is no reason that a standard 2 pole 120/240 GFCI breaker should not work when connected to your A & C phases (max 120V to ground).
 
Re: GFCI for Motor

Al and Jim, Yes. All three breakers used the high leg first. If that's been the culprit then I guess I was wasting good dollars, trying to save one lousy space in a pretty full loadcenter for a future 120 circuit.
Sheez.
 
Re: GFCI for Motor

Sorry to be the bearer of bad news.

Evidently the detection circuitry is bridging both hot legs to the neutral for its own use. . .the electronics in the circuit on the High Leg side will get 208 Volts impressed on it. Instant green goo.

Solid state devices, unless carefully designed to the contrary, have a very limited tolerance of overvoltage.
 
Re: GFCI for Motor

Of course, which is why the GFCI was labeled "120/240." Doh! So obvious now. The old reading of labels. (Which is why we shouldn't paint over them!)
Another problem,
my roof leaks, but on dry days when I go up there, it isn't leaking...
 
Re: GFCI for Motor

Jim hit it on the head. If you went either A-C or A-B in either case is you hook that pigtail white wire to the center tap of the lighting tap which is not a neutral for the way you wired the L-L of the breaker and it'll fry the breaker.
It would have best not to attach that wire at all. The breaker would work but then you have the problem that the breaker is not rated for that application. As Jim said it's a 120/240 device. The device has been tested at 120v to ground so wouldn't you have 277v should the A phase go to ground considering that the center tap of the B-C is grounded? A 120/240v rated breaker is expecting to see 120v.
 
Re: GFCI for Motor

templdl,

The connection of the GFCI 120/240 V Line Side neutral is required, even with a straight 240 Volt load and no load side neutral.

Case in point, read page three of this four page Cutler Hammer .pdf document.
 
Re: GFCI for Motor

Ive seen high legs on 120/240 3 phase Delta ranging from 180 to 210 volts. Never 277. But your point is well taken. The two pole GFCI was rated 120/240 and was basically hooked up on 120-208/240. I would agree with Al that a connected line neutral is necessary for GFCI operation regardless of the load side or reading an PDF file.

So, I wonder if a brown out would destroy a GFCI as easily as a spike or higher voltage would?
 
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