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Old 07-08-2013, 08:39 PM   #61
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Re: RV Electrical Safety

This info is why"I'm being that guy and asking the curiosity questions that everyone is nice to answer....oh...thank you for more home work
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Old 07-08-2013, 08:58 PM   #62
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Re: RV Electrical Safety

Speaking of "bootleg" grounds: I learned today that Ideal Industries offers a tester which, in their words, "Identifies false (bootleg) grounds." Made me wonder whether Mike had been talking with their product engineers and the "bootleg" term survived all the way from engineering to marketing and sales. Unfortunately the Ideal people left out "reverse polarity" in the naming of that feature.
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Old 07-08-2013, 09:15 PM   #63
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Re: RV Electrical Safety

Quote:
Originally Posted by family wagon
Speaking of "bootleg" grounds: I learned today that Ideal Industries offers a tester which, in their words, "Identifies false (bootleg) grounds." Made me wonder whether Mike had been talking with their product engineers and the "bootleg" term survived all the way from engineering to marketing and sales. Unfortunately the Ideal people left out "reverse polarity" in the naming of that feature.
The term "bootleg ground" has been around 40 years that I know of, beginning with upgrades to ungrounded wiring in the 70's. Ideal doesn't acknowledge RPBG's in their product literature because they didn't know the difference between a CPBG (Correct Polarity Bootleg Ground) and an RPBG (Reverse Polarity Bootleg Ground) until I brought this to their engineering department's attention. See my video using a SureTest on an RPBG at



Also note that if you add at least 15 feet of Romex feeding a secondary outlet from any sort of a bootleg grounded outlet, it will fool these ground loop impedance testers completely. Hey, I'm not making this stuff up. When I figured this all out two years ago I was SURE everyone knew about RPBG's and how dangerous they are. I knew about bootleg grounds 40 years ago as an electrical apprentice, and knew how to avoid making the ground "hot" by using a neon bulb to act as a rudimentary NCVT. But the idea of Reverse Polarity Bootleg Grounds being possible and certainly dangerous seems to have slipped through the cracks since it's not a code compliant connection to begin with...

So, just how many RPBG's are out there? Nobody knows, since you can't find them with a 3-light tester or simple metering. You MUST establish an earth-ground reference to know for sure.

Mike Sokol
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Old 07-08-2013, 09:34 PM   #64
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Re: RV Electrical Safety

Quote:
Originally Posted by jmsokol
Also note that if you you at least 15 feet of Romex feeding a second outlet from any sort of a bootleg grounded outlet, it will fool these ground loop testers completely. Hey, I'm not making this stuff up. When I figured this all out two years ago I was SURE everyone knew about RPBG's and how dangerous they are. But it seems to have slipped through the cracks since it's not a code compliant connection...
Interesting stuff. I have to admit you had me worried while watching that video: it looked like an array of steel handy-boxes with metal face plates, so when I noticed you still holding the one with your left hand while waving around the RPBG with your right hand I thought "uh-oh!" Thanks for mentioning in the audio that it's a plastic box. Whew!

It's amazing what can be tested with circuits on the wire. I worked years ago with a group developing technology for finding faults in aircraft wiring while the wires are in use, in flight, without interfering. Wow.

But even through all the fancy stuff, still it comes down to a DMM with a long wire out to earth and/or NCVT for the reverse polarity combined with faulty ground.

This is probably patentable, but.. oh well. I wonder whether a tester could reliably detect RPBG with a second module connected to a known-good grounded socket. A powerline carrier signal sent over the wire (just over one conductor, or different signals over each) between the reference and the tester carried through the house/facility might help identify polarity reversal.

I dunno, maybe it's just me.. I'm just skeptical of the NCVT for some reason. Can't articulate why, nor even whether I'm worried more about whether it'll give a false positive or false negative.
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Old 07-08-2013, 09:50 PM   #65
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Re: RV Electrical Safety

Quote:
Originally Posted by family wagon
Quote:
Originally Posted by jmsokol
I dunno, maybe it's just me.. I'm just skeptical of the NCVT for some reason. Can't articulate why, nor even whether I'm worried more about whether it'll give a false positive or false negative.
That's because you don't have the luxury of having a test bench that allows you to electrify anything to any voltage potential you like, then test for hot-skin voltages in a bunch of different ways. See http://www.bkprecision.com/education/pr ... stems.html for my test rig.

Since I've tested hot-skin conditions using a NCVT hundreds of times in dozens of different situations, I'm confident it's about as accurate as you can get without being an electrician or electrical engineer. And certainly it's more fail-proof than poking meter probes into rust or paint and not getting a solid contact. That's why I'll only recommend using NCVT's for hot-skin testing that I've personally checked out on my test rig.

Mike Sokol
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Old 07-09-2013, 12:39 AM   #66
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Re: RV Electrical Safety

Actually... I am an electrical engineer, which is why this stuff interests me. Maybe it's just lack of exposure/use of the NVCT, or maybe it's that I prefer to plug in a DMM and look at AC plus DC offset, sometimes haul out the o-scope, sometimes bring a few resistors to see whether an apparent voltage is just stray or whether it really has some power behind it. One of these days I'll have to just get over it and add an NVCT to the toolbox, and I'll probably wonder why I didn't do it sooner!

Regarding the earlier conversation about shock hazard in water:
Quote:
Originally Posted by jmsokol
If you immerse an electrified object (such as a boat) in freshwater, there's not enough water conductivity to actually "ground" the electricity quickly. Think of it was an infinite number of resistors up to 100 feet long extending from the object in a big hemisphere around you. The potential will start at 120 volts near the boat, and gradually taper off to zero volts between 60 to 100 feet away, depending on water salinity and such. Now if you were to put two meter probes in the water about 3 feet apart, you could measure a voltage difference due to this gradient field. If you're way far out from the boat, then you might only read a volt or two between the probes. But come closer to the big voltage divider network (the water) then the same distance between the probes will increase to a lot more voltage. It's a gradual thing, but as you come closer to the energized boat, then the voltage between 3-ft probes will increase to 20 or 30 volts or more.
My first reaction was to object to the comparison because I had been thinking of a single line of resistors, and of course if that were an applicable model then the voltage measured across a 3-ft interval, anywhere along the interval, would have to be the same. But I came across a write-up on Mike Holt's web site that caused me to realize it's more like a tree of branched resistances. The origin is the faulted boat, but the current sinks in many different directions to dock structures, other boats, and of course the soils. So now it makes sense that the nearer a person is to the origin (whatever part of the boat is conductive, ie not a fiberglass hull or paint-insulated metal) then the more of those current branches will pass through the area where the person is.
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Old 07-09-2013, 01:16 AM   #67
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Re: RV Electrical Safety

Quote:
Originally Posted by jmsokol
More on this tomorrow... but I've been talking to my generator manufacturer and NEC contacts and getting my head wrapped around the problem. It's a little tricky, but there's a few simple yet safe solutions, I think.
IMHO the simple answer, though not easily directly acted on, is that the grounding should be set up so that if/when a fault happens a protection device somewhere trips (ie circuit breaker for over-current, or GFCI for current going back any way but through the neutral).

Regarding the issue of ground bonding on generators I think I see both sides of the debate for and against whether they should be manufactured bonded. In a 120v genset, designation of "line" and "neutral" on the wires appears totally arbitrary (on a split-phase 240v model like we have in the US, it actually does matter which one you call "neutral" but L1/L2 are arbitrary). Focusing on the common 120v type, the genny manufacturer could grab either wire off the set and label it neutral and tie the ground to it. The thing is electrically isolated from everything else in the world so it doesn't matter which lead they pick.

With that lack of inherent polarization in mind, I've spent some spare cycles trying to come up with scenarios in which having the generator frame and ground terminal defaulting bonded to the wire called neutral would be definitely valuable -- or, on the flip side, a scenario in which that connection could actually prove more dangerous such that the current practice of leaving the bonding to be done in the field as appropriate is best.

For the latter I'm trying to conceive a scenario in which the generator is isolated from earth or other conductive structure like a building (maybe it is mounted to, or simply sits in, a truck bed), and a load plugged to that generator has a fault such that its hot wire becomes connected to the earth or building. If such a scenario could happen, then if a person were to walk up and simultaneously touch the earth or building and the generator, or even just the body of the truck, then that unsuspecting person would be shocked. I guess the piece I'm missing is this: what sort of fault on that load device could complete the puzzle, and how probable is it? A portable lamp with a frayed cord? A power tool with internal damage on its motor windings or speed control switch? A cordless tool battery charger knocked into a puddle on the job site? Hmmm.

Definitely when the generator is connected to something that has contact to earth and all else -- something like a building, an RV with leveling jacks, tongue jack, etc -- then it's important to have the ground-neutral bond done correctly and a good ground connection. But when the generator is used loose, as on a job site etc, I'm tending to think it's actually better that it not be internally bonded.
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Old 07-09-2013, 09:03 AM   #68
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Re: RV Electrical Safety

Quote:
Originally Posted by family wagon
I dunno, maybe it's just me.. I'm just skeptical of the NCVT for some reason. Can't articulate why, nor even whether I'm worried more about whether it'll give a false positive or false negative.
Family_Wagon.... shoot me a PM or email me at mike@noshockzone.org and I'm going to send you a FREE Fluke VoltAlert to play with and report back to the group about how well it works for detecting hot-skin and RPBG conditions. You'll need to wire up your own test RPBG outlet and plug in something with a ground plug to see this work, but I'm sure you'll be a believer in how easily an NCVT will work for casual users. I use my wife's toaster oven to demonstrate appliance hot-skin testing in a kitchen, and a VW microbus model to show small scale RV hot-skin testing during my seminars.



For the rest of you: Yes, this demonstration is REALLY dangerous and could kill somebody if you don't know what you're doing. But I'm trained how to work safely around live voltage and have set up this demonstration on a weekly basis. I'm confident that Family_Wagon has the proper background and will exercise all safety procedures.

Mike Sokol
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Old 07-09-2013, 01:05 PM   #69
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Re: RV Electrical Safety

Quote:
Originally Posted by family wagon
Interesting stuff. I have to admit you had me worried while watching that video: it looked like an array of steel handy-boxes with metal face plates, so when I noticed you still holding the one with your left hand while waving around the RPBG with your right hand I thought "uh-oh!" Thanks for mentioning in the audio that it's a plastic box. Whew !
Hey, I may be crazy, but I'm not stupid

So yes, you are 100% correct. An RPBG outlet will energize a steel box around it to 120-volts AC with full current capacity (20 or 30 amps). And that's why I selected plastic boxes and covers for this demonstration, even going to nylon screws holding on the covers. Also, if your RV is plugged into an outlet mis-wired with an RPBG, even turning the circuit breakers off in your RV's circuit breaker panel WILL NOT disconnect your chassis from hot ground and the the hot-skin condition it causes. So proceed very carefully if you find one feeding your RV. Disconnect shore power at the source and THEN figure out what's wrong with the outlet wiring.

On a side note, one thing I've not written about here is the fact that a GFCI protected outlet would save you from electrocution in most all of these cases. In fact, the only code compliant way to hook up a non-grounded branch circuit is to use a 3-wire outlet that's protected by a GFCI, and to write on the outlet cover "NO GROUND". Most people don't realize that a GFCI breaker or outlet doesn't require a ground wire to operate at all, so it should protect you from electrocution. However, many times when a GFCI trips it's considered to be a random event, so they just move their extension cord to a non-GFCI outlet and plug in. That's a BIG mistake since the GFCI is just doing its job and trying to save your life.

Mike Sokol
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Old 07-19-2013, 03:31 PM   #70
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Re: RV Electrical Safety

Here's my latest article on RPBG outlets which just posted in EC&M Magazine. The online copy is available now, and the print version will hit the streets on July 28th, I think. Here's the direct link to the article: http://ecmweb.com/contractor/failures-o ... ng-exposed

Please contact me with any comments or questions about hot-ground situations, especially as they apply to your RV/Skoolie builds.

Mike Sokol
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