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Old 02-27-2011, 04:30 PM   #21
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Re: 30 Amp / 50 Amp

Originally Posted by RevBill
.. I had to save that to show my class .. hope you don't mind ..
Actually, I do mind.

Originally Posted by RevBill
.. edit .. btw .. your analogy of how a GFCI works is completely incorrect .. not trying to be rude .. but that is completely off-base and bad information ..
Analogies by their nature are inaccurate. That analogy is easy for non technical people to understand. It is actually conceptually pretty bang on. Granted, in the multiple GFCI in the stream scenario, the responsiveness of individual GFCI circuits will vary, so not all will necessarily trip.

Originally Posted by RevBill
.. I'll say it again .. if you guys figure out how to safely install a GFCI on a GFCI-protected circuit and not trip it, I'll be happy to copy your example .. and make millions off of your ingenuity as long as it can pass UL and NFPA inspection ..

.. in 30+ years of being a certified electrician I have never seen it done .. I have made hundreds of service calls for all sorts of creative and ingenious installations by home-owners, but I have not ever seen one installed and working the way you describe using them .. not unless your GFCI is defective, and they usually fail into the "open" position (meaning they won't work at all) ..

I won't way it "can't happen" to have one fail in the "closed" position, but they are designed to work as described and not work at all if they have a problem .. I've even seen people wedge the buttons on the face to keep them working rather than replace them (gotta love renters and the public who always seem to "know better" than everyone else) ..

.. you can "line-side" the GFCI, by-passing the GFCI, and continue the circuit unprotected to another GFCI .. but you can't hook that second GFCI up to the "load" side without tripping the first GFCI .. can't be done if everything is working as it should be ..

Lorna .. if you are using a GFCI in your camper and you are plugged into a GFCI on your power pole I would have it checked (the power pole) .. something is wrong somewhere ..
I have a method of putting a GFCI on the load side of a GFCI that works 100% of the time. I simply plug my window unit A/C with GFCI plug into the GFCI outlet beneath it.

Another example, when I plug the GFCI plug of the pressure washer into the garage GFCI outlets (required by code here), it works 100% of the time.

The only situation that is supposed to cause a GFCI to fault is if there's actually an imbalance in current flow between line and neutral. I won't say that there aren't other times when the circuit will fault.

This is alarming.
Danger: Typically when a GFCI protection device fails, the switching contacts remain closed and the device will continue to provide power without GFCI protection. According to a study by the American Society of Home Inspectors (published in the November/December 1999 issue of the IAEI News (International Association of Electrical Inspectors magazine), 21 percent of GFCI circuit breakers and 19 percent of GFCI receptacles did not provide GFCI protection, yet the circuit remained energized!
While I have no credentials to back up my electrical experience, I have empirical evidence that this works, and works correctly, in a reproducible fashion. I will proceed with my plans (quite similar to Lorna's actually) based on my own empirical evidence.

Sadly, I don't believe that you and I will come to any agreement on this.

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Old 02-27-2011, 04:38 PM   #22
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Re: 30 Amp / 50 Amp

To get back on topic I ran across this resource earlier today and thought it might be helpful.

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Old 02-27-2011, 06:50 PM   #23
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Re: 30 Amp / 50 Amp

RevBill, I believe your biggest problem is you are operating on the assumption that the Campground pole is wired correctly. Excuse me but..

It has been my experience of over 30 years of camping in campgrounds (FL, GA, NC, SC, TN, VA, NM, TX) mostly public with some private parks, that the power at campgrounds are unreliable. Power surges, power drops, incorrect power, damaged receptacles, incorrectly wired receptacles are fairly standard. I used to carry a little tester plug that would show if the receptacle was wired up incorrectly (I've lost the thing someplace). I usually went thru 3 or 4 sites before getting one that was wired correctly. And I haven't really had a "problem". I did lose a convection oven in my pop-up due to low power (TN State Park).

I have only seen a professional electrician in two public parks... that were working. One was a Ga state park and the other was in Chester Frost (Hamilton County) because some idiot rewired a site and blew out half of the Dallas Island sites.

I really don't care if you put a ground fault anywhere in your conversion. I just know what I will do. I will tell folks what we plan on doing. I will warn them if they are doing something dangerous. I will tell them if they are doing something stupid. And I will let them know how campgrounds tend to be since we have camped for so long and this is our second time at full-timing. But we know enough about electrical from actual practice (we used to remodel houses). We will do what we know works for us.
This post is my opinion. It is not intended to influence anyone's judgment nor do I advocate anyone do what I propose.
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Old 02-27-2011, 11:06 PM   #24
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Re: 30 Amp / 50 Amp

Jim .. I owe you an apology .. I made it personal .. My Apologies ..

Lorna .. you always have an answer .. proceed at your own speed .. if I offended you in any way, my apologies too ..

.. I'll go with what I know, and I am sure y'all will too .. I can agree to disagree and just let it go at that ..

.. best of luck to you both ..

Chance favors the prepared mind. - L Pasteur
Luck is the residue of good planning. - B. Rickey
Travel is fatal to prejudice, bigotry, and narrow-mindedness ... - M. Twain
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Old 02-27-2011, 11:12 PM   #25
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Re: 30 Amp / 50 Amp

GFCI behind a GFCI was covered in another thread.

Basics: There should be only ONE neutral-to-ground bond in an electrical system, and that is at the main disconnect near the campground/house/friend's meter. In any sub-feed panel, whether sub-panel in the same building, out-building, RV or bus, the neutral should be insulated and isolated from ground. Sub-feed panels (like for a bus shoreline) should have one bar for grounds, and another for neutrals. When boondocking, your inverter or genset would provide a neutral-to-ground bond if you disconnect the shoreline and switch the power source. "Mobile" inverters with automatic switch-over on power loss have extra relay poles to isolate the shoreline neutral when on inverter power, and make/break the ground bond.

Experiments: For over a year, I have had a GFCI outlet in the bathroom at the end of daisy-chain circuit string behind an added "upstream" GFCI outlet that protects an outdoor outlet , without realizing "it can't be done." When the question came up, I found that connecting the neutral to the ground of the "downstream" GFCI instantly trips the first, keeping them separate makes the "upstream" happy. I must point out that both the "downstream" neutrals and hots are both connected through each "upstream" GFCI on its protected side. I would imagine that someone tying all the neutrals together with a wire nut so the neutral current bypasses the upstream GFCI would upset the balance and cause tons of headaches.

The original poster of the other GFCI thread had problems popping ALL GFCI circuits attempting to feeding the bus shoreline, with or without a GFCI on the bus. When the neutral in the panel was isolated from ground, the problem stopped.

If you have one GFCI behind another, it may or may not be to code, but it works, at least for the GFCI outlets. If a fault occurs, it would probably be a coin toss as to which one would disconnect first. Once one disconnects, there should be no current flowing to trip the other, but they might both trip in a tie.
Someone said "Making good decisions comes from experience, experience comes from bad decisions." I say there are three kinds of people: those who learn from their mistakes, those who learn from the mistakes of others, and those who never learn.
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Old 02-28-2011, 07:56 AM   #26
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Re: 30 Amp / 50 Amp

Redbear, you make many good points.

In further researching this, I learned that some of the earliest GFCIs didn't monitor for a neutral->ground fault, only for a line->ground fault. There have been many threads about this over on the rv forum ( Many of the people there have electrical and engineering backgrounds, and have explained things fairly clearly. All the modern GFCIs are supposed to monitor for *any* leakage, whether from line->ground or neutral->ground.

I remember growing up a large number of appliances tied neutral to chassis as well as ground to chassis. I remember in particular an older TV set that did this. When plugged into a particular house, it would blow the fuse (yes, a REALLY long time ago). Turned out the outlet in that house had line and neutral reversed.

I also remember when remodeling our home during my childhood, all the sub panels had neutral and ground bonded. I remember we had to unbond them in all but the main panel.

Many many years ago it was common practice to bond neutral and ground pretty much anywhere you could. I'm not saying it was *right* to do so, just that it was common practice.

Any place you have a GFCI behind another GFCI and discover the GFCIs are tripping, there is a cause for it, and you need to discover the cause. It could be very minor, but it also could turn out to be a real safety issue.

Some things I learned in the course of this thread:
  • The purpose of a GFCI is to detect when current leaks out of a circuit. Normally, current goes through the load between line and neutral. Any current that goes somewhere else is an indicator of a problem. That current has to go somewhere, and it's possible a human will be the element completing that path to ground. For safety reasons, it is better for the circuit to stop working than for it to continue to flow current through the wrong path which might include a human. Besides being required by code, GFCI devices are just plain a Good Idea.[/*:m:15qgxghk]
  • GFCIs do not actually monitor the ground connection, and in fact will work just fine in the absence of proper grounding. It is still a good idea to have proper grounding though.[/*:m:15qgxghk]
  • GFCI fail vs fault: Fault is when the GFCI trips, doing its job. This is a clear indicator that current is leaking somwehere in the circuit. Fail is when a GFCI stops detecting current leakage.[/*:m:15qgxghk]
  • large spikes and surges, especially nearby lightning strikes, can cause a GFCI to fail. TEST OFTEN, especially after major storms.[/*:m:15qgxghk]
  • GFCI failure states: A GFCI can fail in either a closed or open circuit state. It is quite obvious when they fail open, but when they fail closed there is no indication unless you test. It appears failing closed is the most common condition. This means you are not protected in this kind of failure. TEST OFTEN.[/*:m:15qgxghk]
  • Early GFCI devices only tested for current leakage from line to ground. Modern ones check for current imbalance, indicating leakage from either line or neutral to ground.[/*:m:15qgxghk]
  • Tracking down line to ground leakage is fairly easy. You simply disconnect all your loads and reconnect them one at a time until you trip the GFCI.[/*:m:15qgxghk]
  • Tracking down neutral to ground leakage isn't always so easy, especially with early GFCI devices.[/*:m:15qgxghk]
  • When run close to the max rated current, GFCI devices are prone to false faulting. [/*:m:15qgxghk]
  • Many heating elements start to leak to ground when they start to break down. This is in fact a failure state, and the heating element should be replaced when it starts to do this. Refers, hot water heaters, electric space heaters, heating element in your a/c or heat pump, engine block heater, etc.[/*:m:15qgxghk]
  • The importance of having only one neutral to ground bond cannot be overstated. The neutral to ground bond should be at the first panel fed by the power company. The neutral and ground must not be connected in the RV, with the single exception of the generator. If running from generator and disconnected from shore power, it is ok to bond the generator output neutral and ground (and probably a good idea to do so, but I've seen arguments on both sides of that issue). Just make sure that the bond at the generator doesn't affect the feed from shore power.[/*:m:15qgxghk]

I've also found this wikipedia article quite enlightening:

I'm sure there's more, but that's all I can think of off the top of my head.

I hope others find this information helpful,
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