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[Mike Sokol]

Here's something I just wrote for the RV (camping) industry detailing how a broken EGC (ground) wire in daisy-chained wiring between campground pedestals (power receptacles) can allow a single RV (camper) to electrify the chassis on multiple Recreational Vehicles in the same area of the campground. Note that even turning off the circuit breakers of an affected RV will not stop the voltage coming into its chassis from the shore power plug. http://rvtravel.com/beware-of-dangerous-reflected-hot-skin-condition/

[Stephen Swaffer]

I just got my hands on the 2017 NEC a couple of days ago.  A new requirement is that all single phase outdoor receptacles rated 150 volts to ground and 50 amps or less and 3 phase 150 volts to ground or less and 100 amps or less must be GFCI protected.  Of course, that will only be enforced on new installs or major remodels, but still in time that would help with this as the camper creating the problem will keep tripping its GFCI receptacle.

This might also affect sound providers used to using 50 amp feeders outdoors as any new venues those will be GFCI protected.  Necessary for safety-but it might mean a little more preventative upkeep to make sure your setup doesn't create nuisance trips.

[John Roberts {JR}]

I just got my hands on the 2017 NEC a couple of days ago.  A new requirement is that all single phase outdoor receptacles rated 150 volts to ground and 50 amps or less and 3 phase 150 volts to ground or less and 100 amps or less must be GFCI protected.  Of course, that will only be enforced on new installs or major remodels, but still in time that would help with this as the camper creating the problem will keep tripping its GFCI receptacle.

This might also affect sound providers used to using 50 amp feeders outdoors as any new venues those will be GFCI protected.  Necessary for safety-but it might mean a little more preventative upkeep to make sure your setup doesn't create nuisance trips.

If the problem is that the EGC is energized, that may not trip the GFCI that is only sensing current in the line-neutral loop.

If the meat puppet gets between the hot skin and real earth bad things could happen.

Of course if the energized EGC flows trip current into the protected neutral that imbalance can trip the GFCI (but it won't disconnect the energized EGC... I had to add a 3 pole relay to break EGC path for my super duper safety outlet).

A panel/branch GFCI upstream of the local pedestal wiring might be protective. It depends on how/where the local EGC got energized.

JR 

PS reminds me of my kitchen, actually almost my entire house.  Hmmm hot water heater...

[Ed Hall]

I just got my hands on the 2017 NEC a couple of days ago.  A new requirement is that all single phase outdoor receptacles rated 150 volts to ground and 50 amps or less and 3 phase 150 volts to ground or less and 100 amps or less must be GFCI protected.  Of course, that will only be enforced on new installs or major remodels, but still in time that would help with this as the camper creating the problem will keep tripping its GFCI receptacle.

This might also affect sound providers used to using 50 amp feeders outdoors as any new venues those will be GFCI protected.  Necessary for safety-but it might mean a little more preventative upkeep to make sure your setup doesn't create nuisance trips.

Stephen,
So if I understand this correctly, I will need to have a GFCI for my 30A power distro if used outside?  Is that a system wide GFCI needed or would GFCI on each sub circuit be acceptable?  120V 30A single phase input to 4 20A breakers circuits.

I just purchased this 30A portable GFCI for my travel trailer. Would this placed before the distro be compliant? 

My thoughts are that as a system wide GFCI it will trip more often because of the additive nature of current leakage to ground.  A power amp that leaks 2mA and a guitar amp that leaks 3mA could trip the whole system. Whereas if they're on separate circuits each with it's own GFCI then it's unlikely to trip anything. Two guitar amps could take down the whole distro instead of just the circuit to the stage stringers. Given the option I would rather replace the 4 20A breakers with GFCI breakers.

Mike, you thoughts on it's use for a travel trailer would be welcome too. I purchased it with the hot skin condition and the recent thread about the fried cable wire in mind. CATV/RV Grounding Issue

As always, thanks for your help and sharing of knowledge.
Ed

[Mike Sokol]

My thoughts are that as a system wide GFCI it will trip more often because of the additive nature of current leakage to ground.  A power amp that leaks 2mA and a guitar amp that leaks 3mA could trip the whole system. Whereas if they're on separate circuits each with it's own GFCI then it's unlikely to trip anything. Two guitar amps could take down the whole distro instead of just the circuit to the stage stringers. Given the option I would rather replace the 4 20A breakers with GFCI breakers.

Yeah, that's the problem with a single GFCI upstream of all the stage receptacles. I would never choose to use a single primary GFCI like this since my company could be blamed for any sound system shutdown from a single guitar amp going rogue. That could even be a contract breaker and cause the loss of a client. My spin is that single GFCI's on each stage outlet would be far better since that will offer the best protection from electrocution, without compromising the integrity of the main sound system.

[Jonathan Johnson]

Stephen,
So if I understand this correctly, I will need to have a GFCI for my 30A power distro if used outside?  Is that a system wide GFCI needed or would GFCI on each sub circuit be acceptable?  120V 30A single phase input to 4 20A breakers circuits.

I just purchased this 30A portable GFCI for my travel trailer. Would this placed before the distro be compliant? 

My thoughts are that as a system wide GFCI it will trip more often because of the additive nature of current leakage to ground.  A power amp that leaks 2mA and a guitar amp that leaks 3mA could trip the whole system. Whereas if they're on separate circuits each with it's own GFCI then it's unlikely to trip anything. Two guitar amps could take down the whole distro instead of just the circuit to the stage stringers. Given the option I would rather replace the 4 20A breakers with GFCI breakers.

Mike, you thoughts on it's use for a travel trailer would be welcome too. I purchased it with the hot skin condition and the recent thread about the fried cable wire in mind. CATV/RV Grounding Issue

As always, thanks for your help and sharing of knowledge.
Ed

I haven't read the code. But Mr. Swaffer's interpretation implies that if the distro is connected to an outdoor receptacle, that receptacle must have GFCI protection. Since this is about new installations of permanently installed receptacles in an outdoor location, what you're connecting TO the receptacle is irrelevant in the eyes of the code. (As this is a new provision of the code, there is a possibility that a future revision may include reasonable exceptions.)

If your distro is "tied in" or uses camlocks, that's not a receptacle, so perhaps in that case you won't need the upstream GFCI protection, if your distro provides GFCI protection to the downstream receptacles.

On the other hand, maybe you could install a 3-phase receptacle without GFCI and only light up one phase. 

[Jonathan Johnson]

My thoughts are that as a system wide GFCI it will trip more often because of the additive nature of current leakage to ground.  A power amp that leaks 2mA and a guitar amp that leaks 3mA could trip the whole system. Whereas if they're on separate circuits each with it's own GFCI then it's unlikely to trip anything. Two guitar amps could take down the whole distro instead of just the circuit to the stage stringers. Given the option I would rather replace the 4 20A breakers with GFCI breakers.

Hmm. So.... let's say you've got a guitar amp with 3 mA leakage plugged into its own GFCI. And same with the bass amp (3 mA, it's own GFCI). And maybe that old Leslie organ is leaking some current, too. Maybe a couple of other things.

Each thing is plugged into its own GFCI, on a 120V single phase distro, but nothing has more than 4 mA leakage, so nothing trips. All total, you've got perhaps 15 mA. All of these devices are connected to a common ground, but that ground is broken somewhere on the way back to the neutral grounding point. So now you've got a 15 mA shock hazard that won't be caught even though everything is on GFCI.

Does that scenario make sense? Scary? Am I missing something?

[Stephen Swaffer]

Jonathan is correct-the code only applies to receptacles installed outdoors.

I agree that the additive effect could be problematic for sound distribution-but the code panels are concerned with safety and they'd rather shut down a show than electrocute somebody.

JR-my point is that if all of the receptacles are GFCI, then the faulty camper will trip its GFCI, since in order for the EGC to become energized that electricity has to come from somewhere.  Of course, if some other fault-say in the camp office or whatever energizes the EGC, then the downstream GFCI's won't provide any protection.

[Mike Sokol]

Mike, you thoughts on it's use for a travel trailer would be welcome too. I purchased it with the hot skin condition and the recent thread about the fried cable wire in mind. CATV/RV Grounding Issue

I think a 30-amp GFCI on your travel trailer's shore power plug is a great idea. Most modern campgrounds now have the 20-amp receptacles protected with a GFCI, but few do the 30-amp receptacle. However, while this would protect your own trailer from a hot-skin voltage created internally (assuming you also lost your EGC ground connection), it can do nothing to disconnect you from a hot ground in your power pedestal due to a reflected hot-skin from another RV's line-to-chassis fault current in combination with lost EGC continuity back to the service panel's neutral-ground bonding point. Nor will it disconnect your RV's chassis from the hot ground caused by plugging into an RPBG mis-wired outlet. While an RPBG is unlikely to occur in a modern campground, I still hear about them in older houses and churches that weren't originally wired with grounded receptacles. So beware of plugging your RV into a garage outlet with an adapter when you're visiting in a friend's driveway. Always check before plugging your big hunk of metal into a strange outlet. And remember, a standard meter test between H-N, H-G and G-N won't discover an RPBG condition. You either need to measure between the EGC contact in the receptacle or RV chassis and the earth itself, or use a Non Contact Voltage Tester (NCVT) to confirm that the EGC voltage is close to earth potential.

[John Roberts {JR}]

I think a 30-amp GFCI on your travel trailer's shore power plug is a great idea. Most modern campgrounds now have the 20-amp receptacles protected with a GFCI, but few do the 30-amp receptacle. However, while this would protect your own trailer from a hot-skin voltage created internally (assuming you also lost your EGC ground connection), it can do nothing to disconnect you from a hot ground in your power pedestal due to a reflected hot-skin from another RV's line-to-chassis fault current in combination with lost EGC continuity back to the service panel's neutral-ground bonding point. Nor will it disconnect your RV's chassis from the hot ground caused by plugging into an RPBG mis-wired outlet. While an RPBG is unlikely to occur in a modern campground, I still hear about them in older houses and churches that weren't originally wired with grounded receptacles. So beware of plugging your RV into a garage outlet with an adapter when you're visiting in a friend's driveway. Always check before plugging your big hunk of metal into a strange outlet. And remember, a standard meter test between H-N, H-G and G-N won't discover an RPBG condition. You either need to measure between the EGC contact in the receptacle or RV chassis and the earth itself, or use a Non Contact Voltage Tester (NCVT) to confirm that the EGC voltage is close to earth potential.

exactly....

Since this thread is talking about hot skin travel trailers... IMO a GFCI at each pedestal "and" a GFCI for the panel feeding the branch the pedestals are on. If the fault to EGC comes from anywhere in that branch it will shut down the entire branch... Not R&R so the show must not go on if any fault is detected. A panel GFCI for the whole branch might be available with more than 5mA threshold for less nuisance trips but I do not know code on that.

As I posted earlier I devised a more complicated system with a relay to disconnect the power & ground if I detected more than 10mA (IIRC?) in the ground path from any source... I wanted to make the ground threshold higher than the GFCI so it could support enough ground current to trip the GFCI if the fault current came from it. This might make sense for an individual trailer power plug device, but I never did negotiate with UL about lifting the ground. I expect that would involve argument and arm twisting. Perhaps in combination with disconnecting the power simultaneously (same relay) like I did in my prototype device might help convince UL.

I am confident it would be safer, but UL is conservative (and expensive) regarding change.  Such a small market I stopped throwing time and money at it.

JR

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