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Alan,
Article 250-2(b) of the ’99 Code says that you must bond to ground (typically at the ground/neutral bar in the service entrance panel) electrically conductive materials and equipment such as metal water piping, metal gas piping, and structural steel members, “that are likely to become energized”.
So, bond water and gas pipes (within 5 ft of their entry into the building in most cases). I’d think that the steam pipes are electrically continuous with the cold water line, because of the feed line into the boiler. Talk to a plumber you trust on that one. You make the call (actually it’s the inspector’s call) on whether to bond the laundry chute.
Section 250-50 discusses requirements for the grounding electrode system. Section (a) requires that a metal underground water pipe (in direct contact with the earth for 10 ft or more) and electrically continuous (or made so by bonding around insulating joints or insulating pipe) shall be bonded to the made electrode (for slab construction, the Uffer electrode, a.k.a. rebar in concrete). I’d do the same for the gas piping if there are any breaks in electrical continuity. Dielectric unions aren’t uncommon in water pipe (especially between the hot & cold side of the water heater), but I’m not sure about gas piping.
I strongly suggest that you read the code (there are a lot of fine points on grounding and bonding), because the requirements vary depending on the occupancy of the building (house vs. high-rise vs. industrial). And talk to your inspector. It don’t matter what the Code says, it’s your local jurisdiction that decides what you gotta do.
Good luck.
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Alan,
Article 250-2(b) of the '99 Code says that you must bond to ground (typically at the ground/neutral bar in the service entrance panel) electrically conductive materials and equipment such as metal water piping, metal gas piping, and structural steel members, "that are likely to become energized".
So, bond water and gas pipes (within 5 ft of their entry into the building in most cases). I'd think that the steam pipes are electrically continuous with the cold water line, because of the feed line into the boiler. Talk to a plumber you trust on that one. You make the call (actually it's the inspector's call) on whether to bond the laundry chute.
Section 250-50 discusses requirements for the grounding electrode system. Section (a) requires that a metal underground water pipe (in direct contact with the earth for 10 ft or more) and electrically continuous (or made so by bonding around insulating joints or insulating pipe) shall be bonded to the made electrode (for slab construction, the Uffer electrode, a.k.a. rebar in concrete). I'd do the same for the gas piping if there are any breaks in electrical continuity. Dielectric unions aren't uncommon in water pipe (especially between the hot & cold side of the water heater), but I'm not sure about gas piping.
I strongly suggest that you read the code (there are a lot of fine points on grounding and bonding), because the requirements vary depending on the occupancy of the building (house vs. high-rise vs. industrial). And talk to your inspector. It don't matter what the Code says, it's your local jurisdiction that decides what you gotta do.
Good luck.
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With regard to gas piping, I don't quite get this. Isn't the gas pipe grounded by virtue of being run underground to the house? Does the meter somehow break the bond? Or is this just for something above ground?
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Bryan--
The idea is to provide a path of very low electrical resistance to ground. Usually the gas supply pipe is wrapped in 30 mil PVC tape (for underground corrosion resistance), and sometimes the supply pipe is non-metallic. And an old black iron pipe can have enough rust or scale built up on it that the resistance is increased.
Also, the gas pipe HAS to be bonded on the customer side of the gas meter. So, yes, if the meter is removed (or non-conductive) and the pipe was not bonded, you'd have non-grounded piping. I don't know whether gas meters are good conductors or not...given the increasing use of plastics, newer meters may well be non-conducting. I'll have to check that out.
All of this is not academic. A plumber working on a Victorian rehab in the San Francisco Bay area was killed by a hot gas pipe. He was opening up a wall and had a good grip on the metal case of the sawzall (had lost the rubber boot off the nose a long time ago). He knew there was a gas pipe in the wall (either shut off or abandoned), and he meant to cut it.
When the blade hit the pipe, he was electrocuted. He could not let go. The gas pipe was somehow tied into the building electrical system. Don't know whether the pipe was in accidental contact with a hot wire, or some idiot intentionally tied the pipe to the electrical system.
And for those of you who are saying, "But, hey, the breaker should have cleared the fault", you're partly right. A breaker will clear a bolted fault (low-resistance fault, AKA "dead" short), but a breaker can pass a low but deadly current indefinitely in a high resistance fault situation. It only takes a couple hundred mA to interrupt the electrical pulses in the heart. He was the low resistance path the current took to ground. A good equipment ground on the tool (y'know, that 3rd pin on the cord that breaks off or that a lot of guys cut off?) would have saved him by providing a lower resistance path to ground. That would've allowed the breaker to open the circuit that was causing the pipe to be hot. A GFI on the sawzall wouldn't have saved him, because the deadly current was not from the tool he was using.
Suggestion: check the extention cord you're using, and what it's plugged into.
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This is probably as good an opportunity to ask this as any. Remember, this question has to do with "how things really work", not with the Code.
I'm in a small town in Georgia, and I keep running across this situation - A house will have a two wire system, and at some point the owner has grounded outlets put in, being told that the electrician was "rewiring the house". In actuality, all the electrican (I use this advisedly) did was replace the old, non-polarized outlets with new grounded oulets, connecting only the hot and neutral.
If this is the case, should the safety-minded but frugal homeowner (who can do electrical work on his own home in my small town) add a jumper from the neutral to the ground lug on each receptacle?
I understand the concept of the redundant path to ground, but it would appear that in actuality the likely break or short in the circuit would occur past the receptacle, that is, on whatever is plugged in there. Then, the ground-to-neutral jumper on the receptacle could fulfill its function of providing a lowest-resistance path to ground.
In effect, I'm asking would adding these jumpers make things plugged into those outlets safer?
I understand all the legal ramifications of any injury resulting from any advice given here or by me. Given that, I still would like some opinions!
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OK, sidestep the obvious code violation here and consider this: someone repairing the circuit you describe inadvertantly reverses the black and white wires upstream of the receptacle with the jumper. You now have a receptacle with a hot ground. You now have a very dangerous situation. This hot-neutral reversal happens very often, especially among do-it-yourselfers. And the jumper you mention is very often found on GFCI receptacles "so the tester will work".
*Forrest--Good question on the "bootleg ground". The purpose of the equipment grounding conductor is to provide an zero potential path to ground (which the neutral isn't), in case the hot or neutral wiring in the appliance comes in contact with a conductive part of the tool or fixture, or whatever. If you touch that metal case or lamp base, you become a path to ground. If you're on dry carpet, or wearing rubber-soled shoes, and you're skin is dry (meaning you're a "high-resistance conductor"), you'll probably feel just a tingle. If you're standing in a puddle and you're sweating, you're a pretty good conductor. So you get a jolt, maybe a visit from the paramedics.Keep in mind that the "neutral" is really a current-carrying conductor. It's only "neutral" when no current is flowing in the circuit. If you measure the voltage and current in the neutral when the load is on, you'd find that the neutral is indeed hot--carrying current. The voltage from neutral to ground will be lower than 120 volts, depening on the resistance & impedence of the load. The current will be the same in hot and neutral.So back to the lamp with a metal base, or drill with a metal case (or sawzall). If there's a frayed wire in the lamp or tool that comes in contact with the base or case, that metal may be hot whenever the appliance is plugged in (if it's the hot wire that's frayed). Or it may be hot only when the lamp/drill is on (if the neutral is frayed and touching the case). If the equipment grounding conductor (the "ground wire") is properly connected all the way back to the panel ground, it's the low resistance path to ground. The breaker pops if the ground fault is solid enough. You're safe, because even if you're sweating like a hog and standing in a puddle, your resistance is still a lot higher than the equipment grounding system. If you bootleg the ground by connecting neutral to ground, you've just set it up so that when the load is on, the lamp base or drill case is HOT! Holy shit, Batman!Think of the ground as an emergency overflow drain.Some tools and appliances are double-insulated and don't have a grounding pin on their cords. Typically these things don't have much, if any, exposed metal that you could touch. The wire insulation is one layer of protection, and the plastic case (of the drill, for instance) is the other. Chance of coming in contact with electricity is 'bout zero.If you think the possibility of a wire fraying (or being cut into or nicked) is small, you're right. But it really does happen. A lot of people get by without a ground (intentionally or out of ignorance) when using tools that ought to be grounded. But some don't. As Dirty Harry said, Do you feel lucky?Sorry to be so long-winded, but it's worth it if I can get across how absolutely wrong it is to bootleg the ground from the neutral in a receptacle outlet.
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I am having trouble understanding this new code change.
Is all that is required is that I bond the "upstream" gas pipe to the water pipes?
What about steam pipes?
Do I have to bond a metal laundry chute?
And on the gas lines, do I have to "jumper" over valves or unions?
Thanks.
Hoping for help.
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You may also want to check out the 1999 Electrical Resource Board posts at:
http://www.mosquitonet.com/~nerc/wwwboard/wwwboard.html
particularly the thread on grounding to a gas pipe, starting at:
http://www.mosquitonet.com/~nerc/wwwboard/messages/4489.html