#6
To his summary posting, I said I'd use a GFCI in two wire mode and not bother with trying to ground it unless I figured it was _absolutely_ necessary to have a ground. A GFCI generally protects people from shocks better than a ground does anyway. There are times where you really do want a ground - ie: computers.
If it was for something potentially life endangering (eg: poolside lighting or a spa heater), I'd bite the bullet and pull new wire.
No. You miss read what I wrote (mistakes included), which was that "there is no difference, it is how you hook up the appliances." You're right of course, you cannot use them interchangeably, but its no irrelevant that they are connected at the panel. I was responding to a person that said the two wires were the same electrically at the panel but electrically different at the end of the wire. That isn't necessarily true.
The neutral and safety ground ARE electrically different. For example, with a load on hot (black) and neutral (white) wires, a voltage difference between neutral (white) and safety ground could be as much as two volts at the receptacle. Why? An important concept. Either end of wire, electrically, is not same. Wire is an electronic component; a concept that makes understanding the code easier. In some cases (ie. in this exampled, safety ground wire), electricity appears to be same at both ends of safety ground wire. In the meantime, both ends of neutral (white) wire are electrically different. Appreciate the concept to understand why code is written. Wires are not considered electrically same at both ends. Even though neutral (white) and safety ground meet at breaker box, still, they are not electrically equivalent in receptacle box.
That just for discussing electricity per NEC concerns. Then it gets even more interesting. For interconnected electronics, if a safety ground does not exist (circuit uses three wire receptacle but is only two wires protected by GFCI), then electronic damage is possible (not probably but possible). NEC does not address transistor safety. Such potential damage to interconnected electronics is beyond the scope of NEC. NEC is only concerned with human safety; not transistor safety. Yes, the GFCI can justify three prong plugs (if marked accordingly with a specific three word, NEC defined, expression). But safety ground also provides functions.
Terms such as 'safety ground' are not NEC specific. 'Safety ground' is used to make the concepts clearer for the reader. In grounding, the outlet safety ground is different from the breaker box safety ground, is different from the motherboard ground, is different from the computer chassis ground, is different from earth ground. All are interconnected. However each is a different ground with different functions. This in part because no wire is a perfect conductor.
Same reason why safety ground wire connects breaker box to water pipe (and in some jurisdictions, a ground is also made to gas pipe). It is not an earth ground. Its function is to remove electricity from pipe - for human safety reasons. Like wire, pipes are also not electrically equivalent at both ends - which is why a safety ground connection must not be made to water pipes elsewhere in the building. Pipes are no long acceptable as a place to dump electricity - even if electricity is only being dumped there during a very intermittent short circuit. Pipes must not be part of any electrical circuit - which is a relatively new concept in the code.
In the original post, noted was that neutral (white) wire and safety ground wire are not same. Proof. Short neutral and safety ground together at receptacle on an arc faulted (protected) circuit. Build a little test plug and prove it yourself. See how long the circuit remains functional. Any short between safety ground and neutral will (eventually) trip an arc fault breaker because neutral and safety ground wire must remain completely isolated; except in breaker box.
Demonstrated by experiment - and so many reasons above - the neutral (white) wire and safety ground wire are electrically different everywhere except where they meet in breaker box.
George E. Cawthon wrote:
I don't have an arc fault protected circuit to test that and I'm not sure how an arc fault protector work. However, I realize that connecting the two at any point makes a parallel path, so any load upstream will send half the current down each wire to the breaker box. If an arc fault protector measures current to the grounding wire, that's a no brainer and not testing is needed. You are simply putting current into a wire that is not supposed to have any current except when something goes wrong. All this is good, but it has nothing to do with what I said. I did not say that you could use either wire, white or green (bare), for a specific function. You cannot interchange the wires or you screw up or loose the function of one or both wires.
trim
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I've done this. I have a GFCI and nothing is connected to the green ground screw on the GFCI.
I understand what a GFCI does. But I can't help but wonder. They tell you that a GFCI is grounded to the box by just the grounding screws. What if the box itself is grounded to nothing? It is screwed to the drywall.
That outlet is not grounded at all. I'd rather be safe than to code. I'd like both. But I wonder if I should use the RED wire marking it green, the hell with a code and connect it in the entrance neutral bar and mark it green.
Would I be safer, although out of code? Or this is overkill and not necessary.
This issue is so simple. Yet, I got around 10 different answers from all those I spoke to about it. 3 of them Licensed Electricians. Disagreeing. One says the water pipe is good. One says it is not. Another says no need at all to ground. Yikes. If Licensed people can't agree, what the heck the average person is to believe? The City Inspector wanted both cold water and hot water pipe AND the gas pipe bonded together. Others say he is out of his mind and one day I get killed because of him. Makes one's head spin.
Chantecleer
According to George E. Cawthon :
It _usually_ is different electrically.
The neutral wire will carry current when anything on the circuit is in use. From ohms law, then, the voltage on the neutral will _not_ be zero. It could be as high as 7 volts (and that's with everything working as it should).
This can cause problems if it's connected to the grounding system, or even if it's improperly used as the ground on a single outlet.
According to Rob :
I appreciate all that.
I'll restate my point. Consider:
1) All new wiring (even in old houses) needs to be up to code. This _includes_ new repairs to old wiring. The code is quite clear on this point. 2) An inspector is perfectly free to exempt you from code specifics based upon his judgement. 3) The inspector's primary goal is to make your building as safe as he can, at the same time knowing you're not going to do a full rewire. 4) The inspector has seen your system, and therefore knows what will be safe and what won't. 5) No-one else other than an inspector should be making these judgements (as per passing a code inspection and other legal considerations).He knows that grounding to your plumbing system will be an improvement, despite the fact that both the NEC and CEC now frown on this.
But _you_ do not know that when you're making these recommendations to others. In fact, grounding to a water pipe may make a bad situation worse. You have no way of telling without seeing their plumbing.
The overall point is simple: in this newsgroup we should ONLY be advising things that are code-legal (pass an inspection), unless we go to the trouble of explaining how to determine whether the proposed practise is safe, and letting them know how to make their own judgement call.
Unadorned/unqualified advice to ground an outlet to a water pipe is _very_ _very_ dangerous.
As I mentioned, this is illegal in US code, and I _suspect_ that it's gone or about to go from ours. The old CEC recomendation was to use caulk BTW. I'd be a little leery of some epoxies "flowing" into the rest of the outlet and jamming the whole thing.
The only safe recommendation without qualification/caveats.
More correctly, the GFCI ground pin is interconnected to the mounting screws. That doesn't mean it's grounded. If the box is plastic without bonding straps, it won't be. If the box isn't connected to a grounding system, it won't be.
Besides, you are _required_ to make ground connections to outlets (where you do install grounds) with a wire under the grounding screw. Implicit grounding via grounded boxes is _only_ (legally) applicable to switches (where you're usually only grounding the cover plate mounting screws). This is why outlets always have ground screws, but switches usually don't.
Probably safer. Once it's on a GFCI, it's overkill in any event, so why violate code?
It seems simple, but, it actually isn't, unless a qualified person _sees_ your system. There is a lot of judgement sometimes required for individual situations, and the only thing you can say for certain is that the code-approved way is sufficient for approvability/legality and insurance. Short of getting an inspector to your house and telling you to use the red wire, or a pipe ground, the only legal option is the 2-wire GFCI setup _alone_.
The city inspector is right. If by "others", you're thinking of me, that's not what I said. I said that the gas pipe should NOT be used as a grounding conductor (path back to ground). It MUST be bonded TO the grounding system, but NOT used as a grounding path. In other words, if there are two grounding connections to the gas pipe, you may have a dangerous situation. [These days most underground gas lines are plastic, so that doesn't count]
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