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[Jamin Lynch]

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?

[John Roberts {JR}]

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

JR

[g'bye, Dick Rees]

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

JR

You quack me up...

[frank kayser]

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

[Jamin Lynch]

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. 

[Mike Sokol]

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... 

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.

[Jamin Lynch]

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... 

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?

[John Roberts {JR}]

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

[Jamin Lynch]

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? 

[John Roberts {JR}]

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

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]

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