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Author Topic: What could cause this GFI problem?  (Read 5738 times)

Jamin Lynch

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What could cause this GFI problem?
« on: November 03, 2014, 12:43:05 pm »

I was doing a small festival last Saturday. We had 9 bands throughout the coarse of the day. The promoter supplied us with a 25k generator and 50 amp spider box. All the electrical checked out OK. We had 120volts at each of the 6-20amp outlets. All the outlets were wired properly according to my tester. No issues.

Everything was running very smoothly for the first 6 bands, until this one band got on stage. We then had a constant GFI tripping problem with one circuit in particular and sometimes another one. We tried several different options and re-tested outlets from the spider box as well as the stage drop that was out. It seemed to to happen every time the bass rig got plugged in. We finally ran the bass guitar through a D/I and went on.

Here where it gets funny. We had the same problem with the next band. Kept tripping the same GFI. Everything tested out OK.

Here's where it gets even funnier. We had no problem at all with the final band. Everything worked perfectly.

Could it had been something wrong with the wiring from the 2 different amps?
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John Roberts {JR}

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Re: What could cause this GFI problem?
« Reply #1 on: November 03, 2014, 01:05:55 pm »

If it walks like a duck and quacks like a duck... maybe it's a duck.

JR
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g'bye, Dick Rees

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Re: What could cause this GFI problem?
« Reply #2 on: November 03, 2014, 01:14:04 pm »

If it walks like a duck and quacks like a duck... maybe it's a duck.

JR

You quack me up...
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frank kayser

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Re: What could cause this GFI problem?
« Reply #3 on: November 03, 2014, 01:22:52 pm »

Could it had been something wrong with the wiring from the 2 different amps?
That'd be my guess.  Two dead (or dying) ducks. 


I just had two brand-new-out-of-the-box surge suppressors (from a well-liked/respected company here) trip GFCI receptacles last week.  Two different GFCI in two different locations (home and work) - figure the odds both were DOA...  New ones in the mail.


Odd things do happen.


quack quack.
frank
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Jamin Lynch

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Re: What could cause this GFI problem?
« Reply #4 on: November 03, 2014, 01:57:23 pm »

If it walks like a duck and quacks like a duck... maybe it's a duck.

JR

Those darn ducks again.

Thanks for the help.  :P
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Mike Sokol

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Re: What could cause this GFI problem?
« Reply #5 on: November 03, 2014, 02:42:55 pm »

Could it had been something wrong with the wiring from the 2 different amps?

Perchance, did the two troublesome bass rigs have a "Surge Strip" for their power? Many of the MOV versions leak a few mA of current to ground. Daisy chained surge strips can easily cause a GFCI to randomly trip.  Were they tube or transistor heads? My old Ampeg SVT head leaked current to ground like a sieve for years. And the really old back-line amps with stinger caps are highly suspect. I wouldn't trust them a bit on my own stage, especially with a DI connection. So if installing a DI or microphone fixed the issue, then it was some sort of chassis-to-chassis current leakage problem. Even more to think about...  :o

I've just about got my ground fault current multipliers (GFCM's?) built. Amprobe sent me five of their line splitters to modify so I'll soon be asking you all for test subjects. (Igor, bring me a fresh brain). It will take some effort to discover if a particular backline amplifier is leaky or not, but in the long run we'll all get a little smarter.
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Jamin Lynch

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Re: What could cause this GFI problem?
« Reply #6 on: November 03, 2014, 02:54:22 pm »

Perchance, did the two troublesome bass rigs have a "Surge Strip" for their power? Many of the MOV versions leak a few mA of current to ground. Daisy chained surge strips can easily cause a GFCI to randomly trip.  Were they tube or transistor heads? My old Ampeg SVT head leaked current to ground like a sieve for years. And the really old back-line amps with stinger caps are highly suspect. I wouldn't trust them a bit on my own stage, especially with a DI connection. So if installing a DI or microphone fixed the issue, then it was some sort of chassis-to-chassis current leakage problem. Even more to think about...  :o

I've just about got my ground fault current multipliers (GFCM's?) built. Amprobe sent me five of their line splitters to modify so I'll soon be asking you all for test subjects. (Igor, bring me a fresh brain). It will take some effort to discover if a particular backline amplifier is leaky or not, but in the long run we'll all get a little smarter.

Come to think about it, one bass amp was an old Marshall Super Bass 100 tube amp. And the other problem GFI with the second band had an old Rhodes (I think) plugged in to it.

Maybe a culprit?
« Last Edit: November 03, 2014, 03:13:46 pm by Jamin Lynch »
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John Roberts {JR}

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Re: What could cause this GFI problem?
« Reply #7 on: November 03, 2014, 04:13:36 pm »

Old amps, especially non-UL old amps may have significant leakage. AFAIK modern products are subjected to hi-pot insulation breakdown testing at 1kV+. (I don't recall the acceptable amount of hi-pot leakage current, it was not zero, but should be below GFCI thresholds.).

JR
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Jamin Lynch

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Re: What could cause this GFI problem?
« Reply #8 on: November 03, 2014, 05:18:26 pm »

Old amps, especially non-UL old amps may have significant leakage. AFAIK modern products are subjected to hi-pot insulation breakdown testing at 1kV+. (I don't recall the acceptable amount of hi-pot leakage current, it was not zero, but should be below GFCI thresholds.).

JR

Would a solution be to have a dedicated drop box with no GFI's specifically for "old leaky" amps?  :o
« Last Edit: November 03, 2014, 05:21:04 pm by Jamin Lynch »
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John Roberts {JR}

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Re: What could cause this GFI problem?
« Reply #9 on: November 03, 2014, 05:39:51 pm »

Would a solution be to have a dedicated drop box with no GFI's specifically for "old leaky" amps?  :o

For the safety of the musician perhaps cut off the line cord.... Make the musician sign a waver so that he knows using an amp that trips a GFCI is a human safety hazard.

These old amps can generally be fixed without hurting the tone. Advise him to find a capable service technician. This should be common sense, and self preservation for the musician.

Explain natural selection to him. 

JR

{edit.. "well your honor, before he died his amp was tripping my GFCI, so I plugged him into an unprotected outlet". [/edit]
« Last Edit: November 03, 2014, 05:47:01 pm by John Roberts {JR} »
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Jonathan Johnson

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Re: What could cause this GFI problem?
« Reply #10 on: November 03, 2014, 05:42:00 pm »

Would a solution be to have a dedicated drop box with no GFI's specifically for "old leaky" amps?  :o

Removing a safety device certainly would prevent it activating.  :o  But could that potentially contaminate the audio ground of other devices? Could it result in a hazardous situation? In that case, I'd probably insist on transformer isolation with ground lift.
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Jamin Lynch

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Re: What could cause this GFI problem?
« Reply #11 on: November 03, 2014, 05:55:18 pm »

For the safety of the musician perhaps cut off the line cord.... Make the musician sign a waver so that he knows using an amp that trips a GFCI is a human safety hazard.

These old amps can generally be fixed without hurting the tone. Advise him to find a capable service technician. This should be common sense, and self preservation for the musician.

Explain natural selection to him. 

JR

{edit.. "well your honor, before he died his amp was tripping my GFCI, so I plugged him into an unprotected outlet". [/edit]

Get a rope.

I hear what your saying. I was really joking about the dedicated drop box thing. Hence the  :o

As far as I know, this hasn't been an issue before with either of these guys. I'm curious why that is?
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Mike Sokol

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Re: What could cause this GFI problem?
« Reply #12 on: November 03, 2014, 09:27:24 pm »

Would a solution be to have a dedicated drop box with no GFI's specifically for "old leaky" amps?  :o

Perhaps this is the spot for a high-threshold GFCI with a 30 mA trip point. Not currently allowed by code in the USA, but certainly better than bypassing a 6 mA GFCI that's tripping.

The irony is that the thing that will make the GFCI trip on power up is the EGC, and that's what's needed to protect the musician from shock in the first place. If the amp had a broken EGC, then the GFCI wouldn't trip when plugged in. It would then only trip if the meat puppet contacted a earth ground while holding the guitar strings.
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Stephen Swaffer

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Re: What could cause this GFI problem?
« Reply #13 on: November 03, 2014, 10:56:47 pm »

Interestingly, Code is perfectly fine with GFCIs being installed without an EGC-you can even feed through to standard 3 prong receptacles without an EGC-in fact disallowed if it goes no where.  Of course, the caveat is that if no EGC is available-and intended for retrofit installs. 

Of course, that would leave an ungrounded situation as far as shielding goes as well.  A questionable solution IMO since you are relying on the GFCI for any protection-but a possibility?
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Scott Holtzman

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Re: What could cause this GFI problem?
« Reply #14 on: November 04, 2014, 12:45:01 am »

Cutting a line cord on the bass players amp?  I value my life too.
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Lyle Williams

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Re: What could cause this GFI problem?
« Reply #15 on: November 04, 2014, 04:32:31 am »

As an aside, if you run into a circuit that trips a GFCI/RCD when a known non-leaky device is plugged in (possibly tripping only when more current is drawn) then the cause may be an extra neutral-ground connection.
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Andre Vare

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Re: What could cause this GFI problem?
« Reply #16 on: November 04, 2014, 09:52:03 am »

As an aside, if you run into a circuit that trips a GFCI/RCD when a known non-leaky device is plugged in (possibly tripping only when more current is drawn) then the cause may be an extra neutral-ground connection.
Don't tell them.

Andre
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Mike Sokol

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Re: What could cause this GFI problem?
« Reply #17 on: November 04, 2014, 10:56:32 am »

As an aside, if you run into a circuit that trips a GFCI/RCD when a known non-leaky device is plugged in (possibly tripping only when more current is drawn) then the cause may be an extra neutral-ground connection.

Yes, and a swapped Neutral and Ground will do the same thing....  :D
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Mike Sokol
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John Roberts {JR}

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Re: What could cause this GFI problem?
« Reply #18 on: November 04, 2014, 05:29:23 pm »

I suspect we could plug the guilty product into a ground lift adapter and probe with a VOM on AC current scale between the chassis and outlet ground to measure leakage. (note: this assumes the guilty product is not connected to anything else that could drain off leaked current.

JR
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Re: What could cause this GFI problem?
« Reply #18 on: November 04, 2014, 05:29:23 pm »


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