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Author Topic: Reflected Hot Skin Voltage  (Read 4115 times)

Mark Cadwallader

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Re: Reflected Hot Skin Voltage
« Reply #10 on: April 02, 2017, 01:43:51 pm »

IIRC, Gary Holt (?) had a write up a couple of years about GFCI devices designed for "upstream" use that had a much higher trip threshold. Something like a 50 amp device; I think I recall pictures and a general discussion, but no specifics.
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Stephen Swaffer

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Re: Reflected Hot Skin Voltage
« Reply #11 on: April 02, 2017, 02:06:17 pm »

There are, in general, 2 types of GFCI mentioned in the NEC.  GFCI for personnel protection and GFCI for equipment protection.  The GFCI for equipment protection is a much higher threshold-generally required for switchgear rated over 1000 amps. The new requirement is for 50 amp branch circuits, code is going to require a listed branch circuit breaker.  I don't think "code" lists a trip current, I belive that is going to be determined by the UL requirement for "listing".
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Steve Swaffer

Ed Hall

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Re: Reflected Hot Skin Voltage
« Reply #12 on: April 02, 2017, 09:07:12 pm »

Thanks to all. You have confirmed what I thought but lack the experience to have confidence in.


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.

I am very much in the Lounge. Some of you guys have more electric in a single amp rack than I need for my system. My "distro" is a single 30A L5-30p into a box with 4 20A circuits. Think construction spider box. Having the breakers swapped for GFCI is not a problem.



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.

Thanks Mike.  That was my thinking, that it would protect my trailer and occupants if the fault was in my trailer. I have the GFCI right after my EMS-PT30X   I'm thinking with both I should be protected from most of the usual electrical problems. I also carry a VOM and NCVT and check everything before connecting anything, both the trailer and in the audio world. Saved my butt/gear more than once! I've read your article on the RPBG but have yet to see one in the wild. But I'm still looking.  8-)

Thanks again for all of your help.  It's one thing to "do sound", it's another to do it right!
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Rob Spence

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Re: Reflected Hot Skin Voltage
« Reply #13 on: May 01, 2017, 11:09:29 am »

A couple of weeks ago I was replacing an outdoor motion sensor flood light for the mother in law in a 1940s house.

The relay that powers the lamps had failed.

I had no test tools with me but having opened up the existing fixture there were just 2 wires wire nutted to the white & black of the fixture. A wall switch inside controlled power to the fixture.

After a trip to the store, I turned off the switch and disconnected the old fixture. In order to get the wires dressed I needed to move the neutral under the bracket. It touched the metal box and zap, long arc then the breaker tripped. Yikes, the wires were not only backwards but the neutral was switched.

Sigh...



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John Roberts {JR}

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Re: Reflected Hot Skin Voltage
« Reply #14 on: May 01, 2017, 12:05:26 pm »

A couple of weeks ago I was replacing an outdoor motion sensor flood light for the mother in law in a 1940s house.

The relay that powers the lamps had failed.

I had no test tools with me but having opened up the existing fixture there were just 2 wires wire nutted to the white & black of the fixture. A wall switch inside controlled power to the fixture.

After a trip to the store, I turned off the switch and disconnected the old fixture. In order to get the wires dressed I needed to move the neutral under the bracket. It touched the metal box and zap, long arc then the breaker tripped. Yikes, the wires were not only backwards but the neutral was switched.

Sigh...



Sent from my iPad using Tapatalk HD
Glad you are OK...

NCVT are your friend.

JR
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John Roberts {JR}

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Re: Reflected Hot Skin Voltage
« Reply #15 on: May 01, 2017, 12:11:20 pm »

It is perhaps worth repeating that the 5mA GFCI trip current is specifically set for human safety (to prevent muscular contraction and getting stuck on the shock).

Nuisance trips caused by rouge gear should only be a nuisance once, unless the owners are gluttons for punishment.

JR
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Don't tune your drums half-ass. Listen to what a properly "cleared" drum sounds like.   http://circularscience.com/

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Re: Reflected Hot Skin Voltage
« Reply #15 on: May 01, 2017, 12:11:20 pm »


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