GFI and outdoor stage.

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markebenson

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I have an outdoor stage with gfi outlets for bands. Also on the stage is a 12 channel xlr connection box for audio only (non-powered). The cable from the audio box goes through the wall to a mixer indoors. It the indoor mixer required to be GFI protected also?

Thanks!stage.jpg
 
Required or not, it's probably a good idea-- there's a 'tradition' with bands that the mike stands are sometimes electrified. By accident.
 
PaulMmn said:
Required or not, it's probably a good idea-- there's a 'tradition' with bands that the mike stands are sometimes electrified. By accident.
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It's usually the mics themselves, not the stands, and it's due to grounding issues like ground loops that put voltage on the grounding shield of mic cables or on the shield of guitar cables. Things are better now that guitar amplifiers and PA equipment made since the 1960's or so have three prong power cables.

My 1967 Fender Super Reverb originally (retrofitted now) came with a two prong unpolarized power cord and a "suicide switch" that connected the chassis to one pole, the other, or neither of the AC supply lines through a capacitor. It got me shocked many times when I touched a mic and my guitar strings at the same time, usually on the lips. Ouch.
 
ggunn said:
It got me shocked many times when I touched a mic and my guitar strings at the same time, usually on the lips. Ouch.
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Reminds me:
When I was a kid, I was at a movie theater and walked over to the water fountain. Knowing that winter increased static shock, I carefully touched only the plastic knob, leaned in, and *ZAP* my lips got a shock.
 
ptonsparky said:
MDSW had an electric fry pan when we were young. She was stirring gravy with a metal spoon when I leaned in for a quick kiss. One of my hands was on the kitchen sink. Dang near got both of us at one time. I shot holes in it right after the gravy was done.
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I think the worst hit I ever took from that Fender Super before I rewired it was when I was playing in a high school gym. The pullout seating had a way it could be deployed where it would make a stage instead of bleachers, and I was wearing leather soled boots. I stepped on one of those carriage bolt heads while I was playing a solo and it damn near took me out.
 
markebenson said:
I have an outdoor stage with gfi outlets for bands. Also on the stage is a 12 channel xlr connection box for audio only (non-powered). The cable from the audio box goes through the wall to a mixer indoors. It the indoor mixer required to be GFI protected also?

Thanks!View attachment 2566554
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FWIW, back when I ran sound a lot in live venues I powered the FOH equipment with a heavy duty extension cord back to the same source as the onstage gear. The PA was always quieter (noise wise) that way. If you did that the question would be moot.
 
My guess is a old tube amp has a internal transformer to boost the voltage way up for the tubes. So if way back when all amps were tube they had GFCI's and a ground fault was after the tube transformer (in the amp) the GFCI would not see the fault and thus not trip.
 
tortuga said:
My guess is a old tube amp has a internal transformer to boost the voltage way up for the tubes. So if way back when all amps were tube they had GFCI's and a ground fault was after the tube transformer (in the amp) the GFCI would not see the fault and thus not trip.
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All the good guitar amps are still tube amps (my opinion), and yes, they have rectified transformers to generate the high DC voltages the tubes need to operate. I don't know what you mean by the rest of that.
 
ggunn said:
All the good guitar amps are still tube amps (my opinion), and yes, they have rectified transformers to generate the high DC voltages the tubes need to operate. I don't know what you mean by the rest of that.
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If the hi-voltage side is ground faulted a GFCI wont detect it. You'll still get a shock.
 
Here is a example tube power supply schematic. Everything to the right of the red arrow a GFCI can't see due to the isolation transformer in the power supply:

Tube_supply.png
 
LarryFine said:
How would earth become part of the shocking current pathway?
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When my amp shocked me as I related in post #7 the high voltage DC wasn't the source of the voltage. It was the AC side of the circuit because the way the amp was designed, the chassis was either floating or connected to one pole or the other of the AC power through a capacitor through what was often referred to as the "suicide switch", and the AC came in through an unpolarized plug. The shield of a guitar cable is connected to the amp chassis and the strings of an electric guitar are connected to the cable shield. The steel underpinning of the gym stage was obviously grounded and the sole of my boot was obviously conductive. Zap.
 
Most of the time, the mic is providing the good solid ground and the leakage current is coming from elsewhere. As mentioned, it could be an amp, or even the heater of a baptistry (that caused a fatality). A GFCI on the mixer wouldn't help in that case. One on the backline (or baptistry heater) would.
 
tortuga said:
Signal ground tied to the chassis of equipment.
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Signal grounds are isolated from chassis ground by capacitors, and in a modern amp the chassis is solidly grounded. I guess in an older amp a cap could fail to a short, but that would blow the main fuse to the power supply. At any rate, I never heard of anyone getting shocked on stage by high voltage DC from a guitar amp. Working inside a tube amp, though, even one that has been turned off and disconnected from power, is dangerous if one does not bleed the potentially lethal voltage from the isolation caps.
 
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