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Old 07-10-2019, 04:37pm   #1
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Default Any electrical experts here - Variacs and GFCI's

I have a code issue at work that I am having difficulty getting a clear answer on. We have numerous variable auto-transformers (variacs) that are within the range where GFCI is required. These are relatively new in age so the GFCi requirements were in place at the time of installation and of course the manufacturer is no longer in business.

I have read various reasons whey they are not GFCI - GFCI is ineffective below 100 volts, GFCi will trip due to being too sensitivity incompatibilities, etc. Has anyone had any experience with this that could shed light on to why these were not connected to GFCI originally, otherwise I may need to setup a test area
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Old 07-10-2019, 04:57pm   #2
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I'm assuming this is a non-isolated VAT. Could you run an isolation transformer upstream and then use a GFCI?

Or, are you trying to GFCI the output?
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Old 07-10-2019, 05:54pm   #3
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Any properly wired Variac should not upset a decent GFCI breaker.....

now, turning it on/off with a power switch MAY trigger the GFCI, my electric shaver does that to the GFCI breaker in the bathroom, it is one of two on the same circuit but only the one with the shaver goes off when shaver is turned off...just reset the GFCI, and hell with it....

Obviously referring to the main power switch on the Variac.....now as to load, I dunno, not messed with that configuration.....I would be more tempted to put the GFCI on the output....but that depends on your use, and why you need either one.....
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Old 07-10-2019, 07:13pm   #4
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Originally Posted by ZipZap View Post
I'm assuming this is a non-isolated VAT. Could you run an isolation transformer upstream and then use a GFCI?

Or, are you trying to GFCI the output?
If I understand correctly, that is one of the questions I have, is there a difference between putting a GFCI outlet for the output or using an GFCI breaker on the 120 side
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Old 07-10-2019, 07:16pm   #5
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Originally Posted by mrvette View Post
Any properly wired Variac should not upset a decent GFCI breaker.....

now, turning it on/off with a power switch MAY trigger the GFCI, my electric shaver does that to the GFCI breaker in the bathroom, it is one of two on the same circuit but only the one with the shaver goes off when shaver is turned off...just reset the GFCI, and hell with it....

Obviously referring to the main power switch on the Variac.....now as to load, I dunno, not messed with that configuration.....I would be more tempted to put the GFCI on the output....but that depends on your use, and why you need either one.....
One issue is these often run 24 hours/day with no one around, so tripping a GFCI will result in lost production if no one is around. If it only happens when turned on or off, that can be managed but if it trips the GFCI at random times, thatís a no go
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Old 07-10-2019, 08:23pm   #6
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If I understand correctly, that is one of the questions I have, is there a difference between putting a GFCI outlet for the output or using an GFCI breaker on the 120 side
I think the biggest difference is that a normal GFCI will not work very well below the rated voltage, so being on the output might be problematic.

I would think a decent isolation transformer would get rid of the fluctuations driven by the load in the VAT draw. So 1/1 isolation transformer on the line, and then the VAT plugged into that.

If everything is grounded properly the GFCI should still serve as protection, even if the problem occurs in the ultimate load, as the imbalance will show up back at the outlet.
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Old 07-10-2019, 08:32pm   #7
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Quote:
Originally Posted by mrvette View Post
Any properly wired Variac should not upset a decent GFCI breaker.....

now, turning it on/off with a power switch MAY trigger the GFCI, my electric shaver does that to the GFCI breaker in the bathroom, it is one of two on the same circuit but only the one with the shaver goes off when shaver is turned off...just reset the GFCI, and hell with it....

Obviously referring to the main power switch on the Variac.....now as to load, I dunno, not messed with that configuration.....I would be more tempted to put the GFCI on the output....but that depends on your use, and why you need either one.....
I would agree that a VAT powering a stable load should be fine, but if the load is changing, the single coil characteristic of the VAT will definitely cause imbalances on the input power that could trip the GFCI.
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Old 07-11-2019, 02:29am   #8
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Quote:
Originally Posted by ZipZap View Post
I think the biggest difference is that a normal GFCI will not work very well below the rated voltage, so being on the output might be problematic.

I would think a decent isolation transformer would get rid of the fluctuations driven by the load in the VAT draw. So 1/1 isolation transformer on the line, and then the VAT plugged into that.

If everything is grounded properly the GFCI should still serve as protection, even if the problem occurs in the ultimate load, as the imbalance will show up back at the outlet.
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I would agree that a VAT powering a stable load should be fine, but if the load is changing, the single coil characteristic of the VAT will definitely cause imbalances on the input power that could trip the GFCI.
Thank you, it sounds like it may be fine but it may be time to set up a test location by changing to a GFCI breaker and seeing if it is stable or trips
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Old 07-11-2019, 03:34am   #9
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So, to get this straight, you are in an industrial application here, and some code or other demands you have a GFI breaker on this appliance.....why?? what it doing? reducing voltage to some heater dealing with water??
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Old 07-11-2019, 06:08am   #10
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So, to get this straight, you are in an industrial application here, and some code or other demands you have a GFI breaker on this appliance.....why?? what it doing? reducing voltage to some heater dealing with water??
Wet chemistry labs, these are on fume hoods to supply variable power to research equipment. Safety staff who donít understand all the nuances of reality are citing it as deficient as they are within 6í of water. I agree that that would normally dictate GFCI but Iím trying to determine why they were not set up that way to begin with, and were approved by the electrical inspector
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Old 07-11-2019, 07:36am   #11
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Quote:
Originally Posted by Black94lt1 View Post
Wet chemistry labs, these are on fume hoods to supply variable power to research equipment. Safety staff who donít understand all the nuances of reality are citing it as deficient as they are within 6í of water. I agree that that would normally dictate GFCI but Iím trying to determine why they were not set up that way to begin with, and were approved by the electrical inspector
Well, I bet these two thought have crossed your mind already....one is that the plant/wiring/setup predates the invention of GFCI by some years....so in fact is grandfathered in??

I think that if the load it fairly steady on the Variac, there should be no trouble running off a typical household GCFI, now it it's a switched load coming on/off all the time....all bets are off.....especially if it's an inductive load taking something like ten amps.....the kick on/off by the switch will throw the breaker almost for sure, if my silly little shaver can induce enough kick to toss the breaker, that Variac good for 15-20 amps sure as hell will....

You know, I forgot, how about a surge supressor power strip plugged into the GFCI and then to the Variac, AND maybe one into the variac output to the load plugged into the strip.......

gotta kill that surge somehow.....that's watt she said.....
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Old 07-11-2019, 08:56pm   #12
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Well, I bet these two thought have crossed your mind already....one is that the plant/wiring/setup predates the invention of GFCI by some years....so in fact is grandfathered in??
2004 build, ~$100 million, no expenses spared, problem now is we have limited documentation as not everything stayed with the facility when it was sold. Knowing it was inspected leads me to believe there is a reason why it was not GFCI, I just donít have those records
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