Determining neutral vs. ground

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  #1  
Old 05-24-01, 09:07 AM
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Recently I undertook to replace the standard recepticle on my outdoor patio with a GFCI. Upon removing the old one, I noticed that of the three attached wires, two were yellow (!) and one was white. I determined that one of the yellow wires was the hot. But I can't figure out which of the remaining two is ground and which is neutral (assuming that one is in fact neutral and the other is ground). There is continuity between those two wires, and a plug-in circuit tester reads correct both when the non-hot yellow is connected to the ground screw of the GFCI and white to neutral, and vice versa. How can I tell which is which? By the way, my knob and tune system is grounded throughout (circuit tester shows correct wiring at all outlets, and all except this one have the expected black, white and green). The grounding was accomplished by running ground wires to various cold water pipes.
 
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Old 05-24-01, 10:03 AM
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Hoo-boy! The individual who ran separate grounds to various locations on your water system was obviously not aware that this is not permitted. All grounds must terminate only at your service ground, which is the grounding lug or bus at your main panel. There are many circumstances under which you could energize the water piping by having your grounds connected to it this way. Ground connection to plumbing is to be from the service ground in your main panel to a point on the piping that is within 5 feet of the water service line's entrance into the building, where this service line has at least 10 feet of contact with the earth outside your building.

Next, of course you will read continuity between neutral and ground because they both terminate to a single point in your main panel where they are bonded together.

With a knob & tube system having both hot and neutral with black insulation, it is difficult at best to have all the polarity consistent in your home. From all the K&T I have seen it appears there was no concern about polarity when this system came along, and no polarized plugs or receptacles. I'm at a loss to understand how or if the original installing electrician paid any attention as to which is which when connecting lights & receptacles.

Maybe I'm forgetting something here, but the only way I can think of to determine which of those yellows is which would be to physically trace them back to your panel.

Sorry about the bad news.

Juice
 
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Old 05-24-01, 11:15 AM
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Well. That is disburbing news, particularly your comment that there are a number of ways that my water system might be energized. What are those, and how can I prevent them (until I do a complete rewiring, for which it appears that my house is an excellent candidate)? And here's what else is strange -- there is a neutral bus bar, but no ground bus bar (if I'm using the right term) in the service panel. Nor do any of the grounding wires enter the service panel. Although I understand that there should be continuity between neutral and ground because they should ultimately meet at the panel, how can I be getting continuity between neutral and ground if it appears that they are not bonded anywhere? The only thing I can think of is that somewhere in the system they meet, or that they connected the neutral bus bar in the panel to a water pipe. Any ideas?
 
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Old 05-24-01, 11:25 AM
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Exclamation

Juice - Take a look at NEC article 250-130(c).

eclipse - Can you access the subject receptacle's equipment grounding conductor at the water pipe? If you can, disconnect it. Then do a voltage check like you did before at the receptacle and when you get a voltage reading it's between the neutral and the hot. TURN OFF the power. Identify the hot wire with black tape. Identify the equipment grounding wire with green tape. Connect the equipment grounding wire to the water pipe again. Install the GFCI receptacle per the manufacturer's instructions.
 
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Old 05-24-01, 11:42 AM
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Thanks for the idea, Thinman. I hadn't thought of that. On the subject of energizing my water pipes -- would that happen if there was a short from hot to neutral (or ground)? I'm really concerned about this now, as I don't believe that a fuse would blow quickly enough to prevent electrocution, particularly if, for example, someone was in the bathtub. Also, there is a large (6 or 4 gauge) solid aluminum wire connected to the service panel, but I don't know where it goes.
 
  #6  
Old 05-24-01, 12:35 PM
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Thinman, Since our friend seems to have an ungrounded system I assume someone at some point has engaged in "Nongrounding Receptacle Replacement" as discussed in 250-130 (c).

I take it you are correcting me on the fact that for ungrounded systems you are permitted to run an equipment grounding conductor from a grounding type receptacle to any point on the grounding electrode system, the grounding electrode conductor, or enclosure where the circuit originates, IN ADDITION TO the grounding terminal bar in the service equipment, as I had indicated. Of course you are correct. I realize that I gave him one choice when in fact there are several. If I'm missing your point please let me know.

My initial concern was the existing grounding conductors terminated at various points on the water piping.

Eclipse, the NEC says, in Article 250-50, that "Interior metal water piping located more than 5 feet from the point of entrance to the building shall not be used as part of the grounding electrode system". To correct this you can take those ground wires to any of the points named above. If you must splice additional lengths of ground wire to reach such points, you are required to use an "irreversible compression-type connector listed for the purpose", in other words, a crimp-type connector that says on the package it is for grounding splices or terminations. Wire nut is not permitted for this particular task.

As far as your concern about safety, in my house the previous owner was an idiot who had no reservation about engaging in electrical work despite the apparent fact that he had no idea what he was doing. He hooked up a medicine cabinet over the bathroom sink reversing all 3 conductors, hot to ground, ground to neutral, and neutral to hot. I lived there for two years before I discovered it, and all that time the medicine cabinet lights worked fine and there were no incedents. Until one day by sheer coincidence I was opening the metal cabinet door while simultaneously turning on the water and EEEOOOWWW!!!

I didn't waste any time taking the thing apart and figuring out what the heck this guy did, and re-wiring it properly.

My point here is that you may not have ever had a problem or noticed anything funny, but the potential exists for something bad to happen. NEC seeks to eliminate that potential and prescribes ways to wire things trying to eliminate these kinds dangers.

If it were me, I would try to find the time to locate each ground conductor, maybe a few each weekend, and extend these ground wires to a reliable connection point on your grounding system such as those I mentioned in the second paragraph. If you are unclear on the meaning of some of those terms write back, I will give you some examples in plain english (the NEC has a very distinct and technical way of speaking which is often confusing to lay persons).

Hope that helps.

Juice
 
  #7  
Old 05-24-01, 12:53 PM
resqcapt19
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Juice,
Up until the 90 or 93 code it was permitted to run a grounding conductor from an ungrounded circuit to any point on a metallic water pipe system to provide a ground for that circuit. When were the ground wires installed?
As long as the water piping system is bonded at the service and there are no non-metallic repairs in the metal water pipe system there should be no problem with the water piping becomming energized.
There is no requirement to use irreversible connectors on equipment grounding conductors. That is only required for grounding electrode conductors.
There are circuit tracers available that would identify the wires, but they are expensive ($150+).
Don(resqcapt19)
 
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Old 05-24-01, 01:24 PM
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Talking

Juice - I wasn't disputing your correct observation. Just adding some info.

On the subject of energizing my water pipes -- would that happen if there was a short from hot to neutral (or ground)? answer: circuit breaker would trip.

eclipse - The equipment grounding conductor is normally a non-current carrying conductor. It will only carry fault-current when metallic parts of equipment, etc., become energized. This action will blow the fuse(s) or trip the circuit breaker(s).
 
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Old 05-24-01, 01:42 PM
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Resqcapt19, I re-read 250-50 and realize I must have missed the words "grounding electrode conductor" as it applies to Eclipse's situation, individual equipment grounding conductors.

If this wiring to water piping was done at the time it was permitted back in the '90 or '93 Code, and especially if it happened to be inspected, then you aren't compelled to change it unless you modify or upgrade any of those circuits. I believe resqcapt19 when he says that there is little chance of being energized if this piping is bonded near the point of entrance to the service ground in your main panel. I'm just uncomfortable wherever the words electricity and chance are used in the same sentence. In any event, this was done for many years and apparently permitted for many years, so at least you don't need to freak out over it I guess. Sorry if I spooked ya.

Juice
 
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Old 05-24-01, 02:13 PM
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Let me see if I understand all of this -- if I'm reading correctly, it's okay that there are ground connections to the cold water pipes as long as there is a bond from the service panel to a water pipe. Right? But my service panel is nowhere near the point at which the main water pipe enters the house. Is it okay if the bond from the service panel is to any water pipe as long as there is continuity from that point (as well as the other ground wire to pipe connections) all the way to where the main pipe enters the house? (By the way, some time ago I did run a jumper of 4 (or was it 6? I forget) gauge solid copper wire across the water meter.)
 
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Old 05-24-01, 02:45 PM
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eclipse,

1. it's okay that there are ground(ing) connections to the cold water pipes as long as there is a bond from the service panel to a water pipe. Right?

Thinman - Yes!

2. But my service panel is nowhere near the point at which the main water pipe enters the house.

Thinman - Your service panel doesn't have to be near the point where the main water pipe enters the house. The actual GEC (service panel grounding electrode conductor) connection has to be within five feet or less where the main water pipe enters the house

3. Is it okay if the bond from the service panel is to any water pipe as long as there is continuity from that point (as well as the other ground wire to pipe connections - different system. different rule.) all the way to where the main pipe enters the house?
Thinman - No! See explanation in paragraph 2. Plus it's connected to the cold water pipe.

Thinman - We're talking about two different grounding systems. Don't confuse one with the other.
 
  #12  
Old 05-25-01, 08:18 AM
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What are the two different systems? Also, I take it that this means that I should see where the thick solid aluminum wire attached to my service panel goes. Now, I know that it doesn't travel to the main water pipe entrance point. Should I move it there? (And if I do, how do I route a large gauge bare copper grounding conductor through the bowels of my house?) What if it travels to an earth ground? Is it okay to have grounds connected to various pipes when the panel ground is an earth ground, or must such a system be grounded at the main water pipe entrance? Sorry to be so ignorant about all this.
 
  #13  
Old 05-25-01, 06:09 PM
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Eclipse, sorry about these guys running you in circles to the point your not sure of your name anymore. They said definitly yes, then definitly no, then definitly maybe if. Now you seem to be in worse shape than if none of them said anything to you at all.

Now the real scary part of all this confusion is that if they are not all exactly right, they are all real close to being exactly right, yet the contradict each other drastically.

Read story below, may help you make a judgment. This is your job of making that judgement because this is your home.

Way back when we wired houses without the third wire inclueded now called an equipment grounding conductor. At that time we didn't even have a term ground rod etc. Polarity was also something that was not mentioned at that time so color did not matter. If it worked your were right.

Then we recorded injury and more due to shock factors. The polarity then became a concern. We then started identifying hot and grounded called neutral at the time.

Then we still recorded injury and more due to shock factors. The third wire was added in called an equipment grounding conductor. It took electricians 10 to 15 years to sort out just what that third wire did called an equipment grounding conductor. Some still don't know.

Now we have brought in formal eductation in both union and non union electrical work. Plus we have included data of accidents world wide thus causing change in our wiring designs.

What Juice was talking of is current accepted minimum safety standards. What Thinman was talking about is about the same as Juice was saying. What resqcapt19 is talking about is why I made this explaination for you about wiring designs of the past.

Many people lived their entire lives with wiring we now consider to be dangerous yet most never knew of a problem.

To give you an idea of just the last decade or so. The NEC had approximate of 1500 changes between the 1990 and the 1993 version of the NEC. Between 1993 and 1996 there were about 1500 more changes in that next version of the NEC. Between 1996 and 1999 they pretty well rewrote the whole book yet still in actuallity wiring design change requirements were only about the same 1500 changes. Now we have a new version of the NEC coming out in September of this year called the 2002 International Electrical Code and they again are making many changes in the minimum safety standards in that new book, even introducing new technology called arc fault breakers and more, oh yeah they are moving things around in the book so we can't find it again.

The above should give you some idea as to why the confusion. Even though the new version of the Code is coming out in the 2002 Code, we still have to live with the term called existing. This existing is if it was installed back in great grandma's time and met code then, forever it be in that old code requirements unless you change that original wiring, then you must meet the new current Code requirements.

If you install GFI protection then remove all grounding jumpers. If you don't install GFI protection and these equipment grounding jumpers were installed prior to 1990 then leave them as existing.

As it sounds you have a pretty questionable wiring design that should cause concern. When you can afford it I would rewire the whole house to current standards, thus eliminating the late night scary thoughts in you sleep.

These guys gave you accurate advise, just very confusing to you without much help for you to understand. Hope I shed light on what they were saying as a whole.

Hope this helps

Wg


 
  #14  
Old 05-26-01, 08:19 AM
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Wg,

I am blown away by your careful, historical and insightful explanation. This one gets printed out and saved!

One bit of advice I gave eclipse was to make the time to extend these EGCs (equipment grounding conductors) to any of the allowable points stated in 250-130(c), which I described a few posts ago. Just try to tackle a few each weekend. I realize, eclipse, that with walls closed up and wiring routing often a mystery, that this will be difficult. But even though it was probably allowed at the time the EGCs were wired this way (to the water piping), statistics that wg alluded to showed that shocks and worse were recorded which caused the NEC to improve and tighten the requirements because it is for people's own good.

Wg used the phrase "minimum safety standard", which is all the NEC really is. They do not give advice as to the very best electrical system one could design and install, only the minimum requirements to make it safe, prevent shocks, electrocution and fires. I have said this before - how many people out there do the absolute minimum at their job every day and expect big raises and/or promotions? If you can go "one better" with your electrical system in anything you do to it, I and others in here would encourage you to do so.

That said, if you want the optimum safety for you and your family, you should consider removing a couple pipe-connected EGCs a week and extending them to a known, reliable part of your ground system. I would also find a way, as difficult as it might be, to run a #6 bare copper wire from the main grounding lug/bus bar in your main panel, to within 5 feet of your water service line's point of entrance to your home.

Lastly, I would read Wg's reply again.

Good luck to you.

Juice
 
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Old 05-29-01, 07:15 AM
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Thanks for all the information. One last question, and then I'm done (I hope). It turns out that the large grounding conductor connected to the neutral bar in the service panel does run to a cold water pipe that is within five feet of where the main pipe enters the home. However, although it is within five feet visually, there is somewhat more than five feet of pipe between where it enters the home and where the ground wire is connected, and part of the run is underground. In other words, the water pipe enters the home from the ground, goes through the meter (and yes, there is a jumper across the meter), then goes up a few feet, around a bend, and back down into the ground (presumably this bend is to prevent banging pipes) where it then goes under my floor and pops back out again a few feet away for branch distribution. Is this okay?
|--|
| |
| |
entrance--->[meter]-->| | |<ground wire clamp here
----(floor)--------------|--------|----------------
|------->|
 
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Old 05-29-01, 07:16 AM
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Ignore the attempted diagram, which got messed up in the posting process.
 
  #17  
Old 05-29-01, 04:03 PM
Wgoodrich
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If you have the jumper on the meter and you are connected close but not quite within the 5', I doubt that I would worry about it, just leave that connection alone. YOu might want to confirm you have a ground rod present also connected to the neutral bar of the main panel as required for new installations as a supplemental grounding souce. This is insurance just in case someone removes that metal water pipe and puts in plastic. You would still have the back up grounding source [ground rod]

Wg
 
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