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grounding and bonding


Bradmaj
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I am a master electricain with about 28 years in the trade. Right now I am deployed with the Air Force to a base in Kuwait. There have been sopme issues with people getting shocked out here due to defec tive equipment in the shower facilities.

These facilities are fed from a split-bus panel (illegal in the U.S., I know...), which has a GFCI main breaker feeding each section of the panel. These GFCI's open all three phases plus the neutral in case of a ground fault. Since these panels are fed from a main distribution panel, the grounds and neutrals are NOT bonded together.

An inspection team from the Air Force did a hazard assessment of the suspect facilities and came up with a few recommendations which I do not necessarily agree with. I would like people's thoughts on these suggestions.

First, the team sugggested that all grounds and neutrals be bonded together in all panels, even though they are not the service disconnect. Also, I think that bonding the grounds and neutrals together would cause the 60-amp GFCI mains to nuisance trip all the time.

Secondly, they want to put GFIC breakers on all branch circuits feeding equipment that may pose a shock hazard such as hot-water heaters, even though such circuits are already protected by the GFCI mains. I suspect that if such a remedy was tried, we would again have probLems with nuisance tripping. Usually putting one GFCI breaker "downstream" of another in the same panel causes these tripping problems.

The reason for their suggestions was that they put a meter between the ground and neutral in these panels, and often had a voltage difference between the two points. I tried to explain that anytime you have an unbalance load, (even a small one), there will be a difference in potential between the two points.

Anyway, that's what's going on, and again, I'd appreciate any feedback.

Thanks in advance;

TSGT Scissons

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[#1] Posted: Oct 25 2008 - 03:32:36 AM Reply with Quote

I am a master electricain with about 28 years in the trade. Right now I am deployed with the Air Force to a base in Kuwait. There have been sopme issues with people getting shocked out here due to defec tive equipment in the shower facilities.

These facilities are fed from a split-bus panel (illegal in the U.S., I know...), which has a GFCI main breaker feeding each section of the panel. These GFCI's open all three phases plus the neutral in case of a ground fault. Since these panels are fed from a main distribution panel, the grounds and neutrals are NOT bonded together.

An inspection team from the Air Force did a hazard assessment of the suspect facilities and came up with a few recommendations which I do not necessarily agree with. I would like people's thoughts on these suggestions.

First, the team sugggested that all grounds and neutrals be bonded together in all panels, even though they are not the service disconnect. Also, I think that bonding the grounds and neutrals together would cause the 60-amp GFCI mains to nuisance trip all the time.

Geez, that's not a good idea. All that would do is increase the chance that the electrical equipment could be energized. I can't think of any reason though why having two gfci's protect the same circuit would cause nuisance trips. I also can't think of any reason to have two gfci's on the same circuit. If it was me wiring the place I'd use individual GFCI's for each circuit rather than a main. That way if there's a nuisance trip (I'm not sure with today's gfci's that there's any such thing) it's, well, less of a nuisance.

Secondly, they want to put GFIC breakers on all branch circuits feeding equipment that may pose a shock hazard such as hot-water heaters, even though such circuits are already protected by the GFCI mains. I suspect that if such a remedy was tried, we would again have probLems with nuisance tripping. Usually putting one GFCI breaker "downstream" of another in the same panel causes these tripping problems.

I've never tried this, but I've never worn a belt, suspenders and a condom all at the same time either. I can't see a benefit or a reason why it would cause nuisance tripping. Put a gfci breaker on each circuit and use a regular main.

The reason for their suggestions was that they put a meter between the ground and neutral in these panels, and often had a voltage difference between the two points. I tried to explain that anytime you have an unbalance load, (even a small one), there will be a difference in potential between the two points.

Additionally, the meter creates an electrical path, albeit a very small one, and current will use every available path. Was the voltage difference in the millivolt range or was it even smaller than that?

Now here's the thing, there's this guy named Katen who sleeps in at least three hours later than me every morning. He's lazy but he's smart. Wait for him to respond too.

ok, so his time zone is three hours later than mine

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Thanks for the replies I've gotten so far

#1, the reason I think having two GFCI's on the same circuit would cause nuisance trips is because I put two GFCI's on the same circuit, and they caused nuisance trips, every time something was plugged into the "protected" circuit. It's not much different than putting a GFCI receptacle "downstream" of another back in the U.S. If you do that, as soon as you put a load on the circuit, the first GFCI will trip. Also, having a CFCI main is the Code out here. They use the British standard, which requires such a configuration. I do not even know if Merlin Gerin makes a 240v 50 Hz GFCI branch circuit breaker (Although I suspect they probably do)

#2, the voltage reading from neutral to ground varies from .5v to maybe 12 volts A.C. but 0 amps, which is not unheard of for an unbalanced load

As far as the "I'm not sure that with modern GFCI's there is any such thing (as a nuisance trip)," I can only say that we answer about 25 service calls a DAY here to re-set nuisance-tripped GFCI main breakers.

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Originally posted by Bradmaj

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I am a master electricain with about 28 years in the trade. Right now I am deployed with the Air Force to a base in Kuwait.

Congratulations, better Kuwait that Pakistan or Iraq.

There have been sopme issues with people getting shocked out here due to defec tive equipment in the shower facilities.

These facilities are fed from a split-bus panel (illegal in the U.S., I know...),

Not anymore (2008 NEC) . . .

which has a GFCI main breaker feeding each section of the panel. These GFCI's open all three phases plus the neutral in case of a ground fault.

That seems like an ill-advised configuration. Why open the neutral? Are there three neutral buses? I hope that no one makes the mistake of miswiring a circuit with a hot leg from one of the split buses and a neutral from a different bus. If a main GFCI opens, you'd be in trouble.

Speaking of which, if this is a British system, why are there neutrals at all? I thought that the Brits used 240v for everything? Have I been misinformed?

Since these panels are fed from a main distribution panel, the grounds and neutrals are NOT bonded together.

That seems wise.

An inspection team from the Air Force did a hazard assessment of the suspect facilities and came up with a few recommendations which I do not necessarily agree with. I would like people's thoughts on these suggestions.

First, the team sugggested that all grounds and neutrals be bonded together in all panels, even though they are not the service disconnect.

My first impression is that this would be a bad idea. It would split up the return current between grounds & neutrals causing all sorts of havoc. Besides, if your main breakers are designed to open the neutral, what would then happen with the grounds when a main breaker opens?

Also, I think that bonding the grounds and neutrals together would cause the 60-amp GFCI mains to nuisance trip all the time.

Yes, almost certainly. Of course, that wouldn't be the inspectors' problem, it would be yours. (See, you have to think like an Air Force inspection team.)

Secondly, they want to put GFIC breakers on all branch circuits feeding equipment that may pose a shock hazard such as hot-water heaters, even though such circuits are already protected by the GFCI mains. I suspect that if such a remedy was tried, we would again have probLems with nuisance tripping. Usually putting one GFCI breaker "downstream" of another in the same panel causes these tripping problems.

I don't see why putting one GFCI downstream of another would *cause* nuisance tripping. A GFCI doesn't use any current so it should have no effect on another GFCI. If you're seeing a lot of this type of tripping, perhaps the GFCIs there are different that the ones in the U.S.

Or are they talking about putting a 120v GFCI downstream of a main that's protected by a 240v GFCI? That would be just weird.

The reason for their suggestions was that they put a meter between the ground and neutral in these panels, and often had a voltage difference between the two points. I tried to explain that anytime you have an unbalance load, (even a small one), there will be a difference in potential between the two points.

Well, the only difference should be equal to the difference in resistance between the ground and the neutral, no? Were these people electricians? Were they electricians from the U.S. or from a British Colonial state?

Anyway, that's what's going on, and again, I'd appreciate any feedback.

Thanks in advance;

TSGT Scissons

Well, Sarge, I have only questions.

Please explain the electrical system in more detail. Are we talking about a delta or wye system? Or is it something different? Since you've got neutrals, I'm assuming that you've got some 120v circuits. How do they relate to the 240v circuits? Are you doing things like drawing a 120v circuit off of a 240v circuit, for instance?

My first thought, by the way, is that your people are being shocked by phase to phase or phase to neutral faults which, of course, a GFCI will do nothing to solve.

My second thought is that your inspection team is trying to put an umbrella under a leaking ceiling instead of figuring out why the ceiling is leaking.

- Jim Katen, Oregon

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I would agree with you on the first and second suggested remedies. Even if bonding it all together "fixed it", it is not the source of the problem. No need for GFCI in series as they will cause each other to "nuisance" trip. I would be looking for open neutral or high resistance on nuetral causing current to flow on the ground. Also likely that there is a shared neutral. But I still question how the people are getting a shock before the GFCI trips?

437th CES 88-92

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Hi,

Joe Tedesco, one of TIJ's members, is enroute to theater and will be in Iraq for the next year. You should try to locate him and talk to him about this. Like you, he's got decades of experience as an electrician and he's a sort of electrical educator. I bet that between the two of you you'll be able to figure it out.

S'funny, I thought everything being used over there was 240 volts.

ONE TEAM - ONE FIGHT!!!

Mike

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Sorry, folks, I guess I should have been a little clearer on the voltage configuration here. Yes, it is 240 volt, but that is one hot. Like ours is 120-volts to ground, theirs is 240-volts to ground. A three-phase system is 240-416volts Wye configuration.

And yes, the split-buss panes have two neutral bars. One for the GFCI-protected section, and one for the non-gfci-protected system.

England uses the same voltage they do in Kuwait, 240/416 50 Hz

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Hi,

I'm basically an electrical idiot, so don't mind me if I ask a dumb question; but is it possible that folks just haven't been careful enough about ensuring that all of those grounding rods have less than 25-ohms resistance when they sink them out there? I remember that soil well; it's hard as all get out and there might be stuff there that's allowing too much resistance and is making it real easy for those systems to want to reach out and bite someone.

There are usually dozens of generators running in relatively close proximity to one another and I should think that all it would take is one where there's too much resistance in the soil around the rod and you might have a situation where all it takes is a little water on the soil (such as showers) to create a transient and make it reach out and touch someone.

The army describes a whole lot of methods to use to improve grounds in their manuals but where soil conditions are so bad that less than 25-ohms resistance can't be achieved, they recommend lowering resistance by chemically treating the soil. Here's the formula right from the Army playbook.

c. Treat the soil with chemicals if the ground resistance is still over 25 ohms after using the methods described in paragraphs 1-3a and 1-3b. Treat the soil by-

· Digging a circular trench around the grounding electrode. The trench should be 1 foot deep and 9 inches away from the electrode (Figure 1-15).

· Filling the trench with 50 to 100 pounds of rock salt (copper sulfate or magnesium sulfate may also be used) and then filling the trench with water. As the water goes through the salt into the ground, resistance should be lowered. Natural rainfall will continue the process, but you must replace the rock salt every two years (Figure 1-16).

Figure 1-15. Trench dug around grounding rod

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Figure 1-16. Trench filled with rock salt

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200810266134_grounding2.jpg

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  • 2 weeks later...
Originally posted by Jeff Remas

I am curious as the the grounding requirements due to the type of soil or lack there of (sand) creating a proper ground fault path.

<25 Ohms is required between supplemental rods, but I am not sure that is a good benchmark for a primary grounding point.

Is Tedesco really going overseas?

That's a huge misconception. The "sand" is only a few inches deep except for where it's drifted. Once you get below the sand in Kuwait, Saudi or Iraq you hit some of the hardest sh*t you'll ever try to dig through. Before the air force bombardment phase of DS kicked off, command ordered us to dig bunkers. What a friggin joke! I had nearly 30 guys working round the clock in shifts with picks and shovels to dig a 10 by 16ft. bunker and after 24-hours they'd barely made 18-inches. I finally drove out onto the desert, found 4 brand new latrines that hadn't been used yet, loaded them up on a couple of HMMV trailers, brought them back, stripped two sides off of each of them, and then set them into that hole, leveled them, and stacked sand-filled 55-gallon drums all around that sucker, reinforced the roof and then put on a 3-layer sandbag blast cushion roof. Just as we got it done, Brigade HQ comes down and says that they're going to commandeer it for the secondary HQ in the event of an attack. Yeah right, you should have seen the looks on their faces the morning of the offensive when some panicky twit yelled "gas!" and the entire brigade had to suit up and get in bunkers. They walked up to find my platoon solidly entrenched in there and there was no way they were going to come out and let a bunch of remfs take their bunker.

Anyway, I digress; the "soil" there is very hard strata and it's laced with some kind of light-colored mineral that looks almost like chalk but is hard. Driving ground rods into the stuff is a b***h. You have to try multiple locations in order to find a spot soft enough where you can get the rod to any depth, so you mostly scrape out a trench, lay the rods lengthwise and then bury them.

I think they need to look at the soil composition and how poorly those grounding electrodes are probably being installed.

ONE TEAM - ONE FIGHT!!!

Mike

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