2-wire vs 3-wire circuits and updating

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Old 04-13-04, 11:39 AM
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Question 2-wire vs 3-wire circuits and updating

I have an old house (1959 vintage) with 2 wire plugs and 2 wire cable. Many devices require the 3 wire plugs. Is there a convient way to upgrade to 3 wire plugs? Since the ground in the 3 wire circuits appears to go to the same bar in the circuit box as the neutral (white), can the ground on the 3 wire plugs be connected to the neutral wire in the cable? Is this essentially what happens when you use a 3 wire to 2 wire adapter?
 
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Old 04-13-04, 12:13 PM
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Other than at your main service panel, neutrals must be kept separate from grounds. They are functionally different and dangerous to mix them other than the main panel in your house.
Use the search function and see the many many post regarding the same question.
In summary, most use a GFCI receptacle at the beginning of each circuit to protect the rest of the circuit, and allow you to install 3 prong recepts. You do not get the function of the ground wire, but this is a code acceptable method to get the job done with only minor compromises.
 
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Old 04-13-04, 12:21 PM
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No, you cannot tie the 'ground' pin on a three wire plug to the 'neutral' (white) wire. This will create a safety hazard and will violate code.

In modern wiring, you have the 'neutral' conductor (white) and the equipment grounding conductor (green, bare, or even the metal conduit). These are electrically connected in the main service panel and _only_ in this one location. Current is expected to flow in the 'neutral' conductor, so there will always be a bit of voltage present. Current is _not_ generally expected to flow on the equipment grounding conductor, except during fault conditions.

If you connect the ground to neutral, you run the risk of having current flow through your grounding electrode system, creating a shock hazard.

Two to three prong adapters usually connect to the screw in the center of the receptacle. In many old houses, you had two wires in a metal armor cable ('BX' cable). The armor serves as a ground, and the screw in the center is reasonably grounded.

If you have two wire _cloth_ or plastic cable, then you simply do not have a ground, and the adapter doesn't connect the ground to anything at all.

If you need a three prong receptacle for _safety_, then you can install a GFCI receptacle. Simply leave the ground _not connected_, and put the 'no equipment ground' sticker on the receptacle.

If you need a grounded receptacle for something like a computer, then you will need to run an additional ground wire in the walls to the service panel (there are a few other options; you will need to do some reading.

-Jon
 
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Old 04-13-04, 12:23 PM
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There are a number of things you should definitely not do:
  • Do not interconnect grounding and neutral at the outlet. This is called a bootleg ground, and is very bad. This is not what a 3-wire to 2-wire adaptor does.
  • Do not use a 3-wire to 2-wire adaptor unless the box is metal and supplied by metal conduit that provides a grounding path back to the panel, or unless it is protected by an upstream GFCI.
  • Do not run a grounding wire from the outlet to a nearby plumbing pipe.
  • Do not run a grounding wire from the outlet to a grounding rod.
I know you are now tempted to ask "why not?", but the explanations are long and complicated.
 
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Old 04-13-04, 12:38 PM
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Smile

Gentlemen, Thanks for the information and especially the code acceptable way of using a GCFI plug at the beginning of the circuit. Now, can you tell me a simple method to determine the beginning plug in a given circuit? Thanks again. I have been looking everywhere for an alternative to the 3 - 2 adapters.
 
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Old 04-13-04, 02:35 PM
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Simple?

Here's one way.
  • Shut off the breaker.
  • Go figure out everything that is on the circuit by finding out what is dead.
  • Remove all the receptacles on the circuit, carefully recording and labeling how each was connected. Leave the removed receptacle next to the box it was removed from for reference.
  • Be very careful with switch loops to make sure you don't mess up the wiring. Post back if you don't know what this means.
  • Turn the breaker back on.
  • Use a circuit tester to find the black/white pair that lights it up. Test every pair of wires in every box. Label the hot pairs.
  • Shut off the breaker.
  • You need to put a GFCI receptacle in every box that has a pair of wires that lit up the tester. Use the hot pair for the "line" side of the GFCI, and the other pair(s) on the "load" side.
  • For the other boxes (ones with all dead wires), you can replace the ordinary two-hole receptacle with a three-hole receptacle.
  • Make sure you break out the side tabs on each new receptacle to match the side tabs that were broken out on the old receptacle (if any). Post back if you don't know what this means.
  • Post back for more help if any of the boxes with a switch loop or with broken-out tabs are also the boxes requiring GFCI.
 
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Old 04-15-04, 09:57 PM
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Great stuff.... John.
 
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Old 04-17-04, 08:10 AM
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John,

I read your list of DO NOTs for grouding but am not sure if the following is acceptable.

My older house has a mixture of grounded and ungrounded circuits. To add ground to an ungrounded circuit, I ran a separate ground wire from a grounded junction box to an ungrounded receptacle. Is this acceptable? Thanks.
 
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Old 04-17-04, 09:20 AM
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From what Ive read, and been told, NO. That is not acceptable. That was something I wanted to do too, but was advised it is not 'code' compliant.
"You can't just add grounding conductors between boxes and be within code. You have to do it properly by replacing the ungrounded cables."
This per 'Homer' on the 'Self Help Forum' - Electrical
 
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Old 04-17-04, 10:29 AM
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Les,

I have also heard that it is not code compliant to do what you did, but I cannot support that conclusion in the code itself. The code articles cited are not entirely clear on this subject (to me at least).

What you did may or may not be a violation. Even if it is, however, it is nowhere near as bad as those on the "do not" list above.
 
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Old 04-17-04, 11:21 AM
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..Good point.
If this work was to be inspected, then I guess its taboo.. but if it isnt.. why not.
In my case, in the DR is on old 2 wire/no ground - I think Im just going to leave well enough alone. Those 3 outlets in question are only running minimal luminaires... So Im not overly concerned about them being grounded. They werent for 46years.
I think the max wattage on these outlets is like 202 watts... and rarely all on at the time. I'll just use the existing 'old' outlets until I can find new 'old' 2 pronge outlets!
 
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Old 04-18-04, 05:39 AM
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Jatco,

I also had to replace 3 prong outlets with 2 prong because the incoming cable had no ground. The previous owner did not understand the difference. In my case, I found new 2 prong receptacles at the local Home Depot.
 
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Old 04-18-04, 06:40 AM
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I believe that the code reference (2002) is 250.130(C) Nongrounding Receptacle Replacement or Branch Circuit Extensions which provides a list of ways to connect an equipment grounding conductor. It provides that you can connect an equipment ground conductor to your grounding electrode system, your grounding electrode conductors, to your panel, or to your neutral in your service panel. Not on the list is connecting to the equipment grounding conductor of another circuit.

250.134 Exception 1 specifically mentions that the grounding conductor in 250.130(C) can be run separately from the circuit conductors.

Note: one of John's 'Do Nots' (running a ground to a nearby plumbing pipe) _used_ to be permitted; you should be on the lookout for this in your house. It is no longer permitted because so much of plumbing pipe is going to plastic.

-Jon
 
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Old 04-18-04, 10:14 AM
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Originally posted by lschonbe
Jatco,

I also had to replace 3 prong outlets with 2 prong because the incoming cable had no ground. The previous owner did not understand the difference. In my case, I found new 2 prong receptacles at the local Home Depot.
My HD doesnt carry new 2prong recep's. I havent tried Rona yet.
I will probably be able to use the original old 2prong receps that are in place now...so long as theyre in good shape. Im using one of them now....
http://images.geekazoids.net/dsc00187.jpg
http://images.geekazoids.net/dsc00188.jpg

And to what winnie mentioned about grounding to the water pipe... A definite NO...IMO. Our house was grounded like that originally...and since our incoming water supply was burried in our concret slab, over time, electrolysis took its effect and created a pin-hole leak on our water line in the slab under the house...so the water line had to be re-run...what a PITA that was. Now the panel is grounded to external stakes in the ground.
 
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Old 04-18-04, 10:51 AM
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jatco,

Using the water pipe as an _Equipment Grounding Conductor_ is not permitted, with one exception.

The reason that water pipe is not permitted as the EGC is simply because you cannot depend upon the metal pipe to remain connected. The exception mentioned above applies to the small section of pipe (5 feet) allowed as part of the grounding electrode system.

However using the water pipe as part of your _Grounding Electrode System_ is not only permitted, but if the water pipe meets the requirements for a grounding electrode, it is _required_. Any electrodes in the ground, including the main water pipe, ground rods, buried plates, buried building steel, etc. _must_ all be connected together to form the GES.

In addition, it is _required_ that you _bond_ any metal water pipes to the electrical system ground, so that if a wire contacts the pipe, the pipe won't become energized and shock people. You have to make this bond even if the supply pipe is not suitable to be a grounding electrode.

If you are seeing electrolysis, it almost certainly means some DC component to your neutral current flow.

If you saw seeing electrolysis and you didn't correct the root cause, and your plumbing is properly bonded, then you will see the electrolysis problem again. If your plumbing is _nor_ properly bonded, then you have an unsafe install.

-Jon
 
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Old 04-19-04, 08:48 AM
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Thanks for that info Jon...
When we had that leak and re-ran the water supply, we used PVC, from the pressure reducer valve, around the house, then into the wall between studds, into the attic and connected it to the remaining (orig) copper water supply with the appropriate connector. No grounding was made to the copper line. The remaining copper line is not exposed. I made a wooden box around the pvc-copper connection in the attic...just in case.
There is no water pipe in the ground (that is from the city turnoff valve to our house)..so no metal water pipe is grounded.
Ground is now made by grounding stakes.
I presume this is OK?
 
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Old 04-19-04, 09:06 AM
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By eliminating the external buried metal pipe, you have eliminated using your water pipe as a ground electrode. Since you have replaced your electrical system grounding with ground rods, that part is fine.

Since you have removed the electrical connection between your internal plumbing and the earth, you shouldn't have a problem with electric current flowing through your water pipes into the earth. This should solve the electrolysis problems.

However the copper piping _inside_ your home should be bonded to ground. This is required of all internal metal piping, even if you cannot use the pipe as a ground electrode.

-Jon
 
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Old 04-19-04, 09:25 AM
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So, it sounds like I need to run a ground line from my service panel, up into the attic and try to find a point to attach it to the copper water line. What gauge wire should be used for this? Anything special to consider? Is this a USA code issue or Canadian..or just a general requirement.
Thanks, Jon
Thomas
 
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Old 04-19-04, 01:03 PM
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jatco,

While your copper pipes are in totally enclosed in the walls, I presume that they connect to your various fixtures. This is where the risk comes in.

Because these are water pipes, you must use table 250.66 to determine the size of the conductor. The size of the conductor will depend upon the current rating of your service.

This is part of the NEC in the US, article 250. I presume that it is also part of other electrical codes. I would expect different wire size requirements, since _in general_ when you have an isolated piping system, you need only use a ground conductor that is the same size as the GEC for the circuit which might energize the pipes, not the full size bonding jumper called for by the NEC.

-Jon
 
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Old 04-20-04, 01:07 AM
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Thanks Jon.
I'll check into it
 
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