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Author Topic: GFCI's tripping...  (Read 1341 times)

Jesse Stern

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GFCI's tripping...
« on: October 09, 2018, 07:00:27 pm »

I have often encountered problems with PA systems tripping GFCI protection on generators/pagodas/wall outlets, especially when subwoofers are involved.  Even when the total amps being drawn is well under the breaker threshold.  Why does this happen?  And is there an easy way to disable GFCI protection on a receptacle?

Mike Sokol

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Re: GFCI's tripping...
« Reply #1 on: October 09, 2018, 07:29:15 pm »

I have often encountered problems with PA systems tripping GFCI protection on generators/pagodas/wall outlets, especially when subwoofers are involved.  Even when the total amps being drawn is well under the breaker threshold.  Why does this happen?  And is there an easy way to disable GFCI protection on a receptacle?

Jesse, GFCI's don't trip from excessive over 15 or 20 amps ofcurrent draw due to amplifier wattage. They trip from anything leaking more than 6mA (0.006 amperes) of current. Some amplifiers leak an excessive amount of current to the chassis which can cause problem tripping, but many don't. However, if you have any surge strips with MOV devices (most do), know that a surge strip will often leak at least a few mA of fault current on their own. So if you have two surge strips, that additive current can put your GFCI right at the threshold of tripping.
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frank kayser

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Re: GFCI's tripping...
« Reply #2 on: October 09, 2018, 07:34:35 pm »

I have often encountered problems with PA systems tripping GFCI protection on generators/pagodas/wall outlets, especially when subwoofers are involved.  Even when the total amps being drawn is well under the breaker threshold.  Why does this happen?  And is there an easy way to disable GFCI protection on a receptacle?


Second question first: No.


Number of amps is limited by circuit breakers/fuse. This protection mechanism in most cases has nothing to do with GFCI (unless GFCI is built into the breaker)


GFCI devices ensure all current in on hot is returned on neutral.  These are very sensitive - I believe the tripping threshold is about 6 milliamps (ma).  10 ma across your chest is considered the lethal limit.


Outdoor GFCI seem to take a beating - rain, heat, humidity, bugs, etc.  As they age, they fail.  It does not take long.  In my city's plaza, I've noticed the GFCI devices have been changed out three times in two years.


Why are the ones you're dealing with are tripping with the PA, especially when using subs, is beyond my knowledge.  The GFCI devices trip due to either internal failure, or have detected a current leak somewhere - maybe a power strip with the surge protection devices, MOVs, are leaking. One power strip plugged into another power strip, the leakages are additive, and maybe the cause of the trip.  Maybe old power amps or other devices with capacitor leaking in the power supply.  Vintage garage sale amps are old, and caps start leaking over time.  Just places to think about. 


frank
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Mike Sokol

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Re: GFCI's tripping...
« Reply #3 on: October 09, 2018, 07:45:59 pm »

Here's something I wrote for PSW on GFCI theory that should help you understand what's happening. https://www.prosoundweb.com/channels/av/no_shock_zone_understanding_and_preventing_electrical_damage_and_worse/
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Frank Koenig

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Re: GFCI's tripping...
« Reply #4 on: October 09, 2018, 10:08:23 pm »

I'll add that some older, out of spec, GFCIs can trip due to RF hash on the lines from big-dog power amplifiers with switching power supplies. This can happen even though the (low frequency) leakage current is well below the 6mA threshold used for 20A branch circuits in the US. DAMHIK --Frank
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Lyle Williams

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Re: GFCI's tripping...
« Reply #5 on: October 12, 2018, 06:20:18 pm »

The idea that 6mA is the correct trip level is not supported by global experience.  Many countries have GFCI/RCD trip currents much higher, and have fewer electrical fatalities than the US.

An isolation transformer of sufficient size will defeat the GFCI, but you should not do this.
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John Roberts {JR}

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Re: GFCI's tripping...
« Reply #6 on: October 12, 2018, 06:47:16 pm »

The idea that 6mA is the correct trip level is not supported by global experience.  Many countries have GFCI/RCD trip currents much higher, and have fewer electrical fatalities than the US.

An isolation transformer of sufficient size will defeat the GFCI, but you should not do this.
6 ma +/-  is the US spec for GFCI trips, so no not true for RCDs in other countries. My bench work found it pretty good here.

I do not understand how an isolation transformer can defeat a GFCI as long as the transformer is isolating just line and neutral in series...

If safety ground gets combined with neutral and not kept separate, that is just defeating the purpose of sensing the symmetry of the line/neutral loop. (i.e. don't do that) 

JR
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Lyle Williams

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Re: GFCI's tripping...
« Reply #7 on: October 13, 2018, 03:11:17 am »

Deliverying a separately derived supply, so that any leakage on the secondary side of the 1:1 transformer is seen as just part of a normal load on the primary side.   

Yes, I was saying "don't do that!"
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John Roberts {JR}

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Re: GFCI's tripping...
« Reply #8 on: October 13, 2018, 09:47:31 am »

Deliverying a separately derived supply, so that any leakage on the secondary side of the 1:1 transformer is seen as just part of a normal load on the primary side.   

Yes, I was saying "don't do that!"
not sure I follow.

A simple 1:1 transformer should just extend the GFCI current loop....

If leakage current returns to the transformer isolated neutral, that is the same as using no transformer with current leakage to the real neutral.

Current leaking from the transformer output back around outside the GFCI loop to safety ground (or anywhere else) should trip the GFCI at >6mA. A bootleg safety ground to neutral with or without transformer isolation will defeat the GFCI protection.

JR 
 
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Stephen Swaffer

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Re: GFCI's tripping...
« Reply #9 on: October 13, 2018, 01:30:54 pm »

However, you have to look at the whole circuit-all the way back to the existing transformer that supplies the GFCI.  Properly installed, it has a neutral/grounded conductor (as opposed to grounding conductor) so if you touch the "hot" conductor electricity flows through you to ground-ultimately getting back to the transformer albeit through an alternate path.

If you install a true isolation transformer, there is no neutral/grounded conductor, so if you touch a hot there is no alternate path back to the transformer.  On the surface this is "safer" and some have argued that, but there are several disadvantages to this scheme.  One of the main ones being what happens if there is a short creating an unintentional ground connection.  With an intentional connection, safeguards (gfcis, breakrs, fuses) can work reliably.
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