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updating outlets to gfi in a 1930's house with old nm wiring

updating outlets to gfi in a 1930's house with old nm wiring

Old 10-22-03, 11:06 AM
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updating outlets to gfi in a 1930's house with old nm wiring

I own a 1937 house with old NM brown jacketed cable (2 wire one with a black stripe the other solid). I am in the process of updating my outlets with GFI's and 3 prong outlets downstream of the GFI with all the required marking for this installation without a ground required by code.

I'm in the process of trying to find the line/load so I can install the GFI outlet properly and over this past weekend I have uncovered the following conditions. In a few locations i have found the end of the run (2 wires coming in the box) but in the middle of the run I have found 6 wires and on one outlet 9. (From my research I was expecting to find only 4 wires.) Of the 6 coming into the box 2 have the black stripe and are pigtailed together, 2 are solid and are pigtailed together, another 2 are solid and pigtailed together and on some of the older outlets there is a connector wire connecting 2 of the terminals with the solid wires (on the same side of the outlet). I am confident there is no ground in this system. What is that 3rd pair of wiring? (I think one pair is hot, the other neutral and the 3rd??? I don't know.)

In order to find the line side for the GFI i need to break apart the existing wiring with the pigtails. How do I do this without damaging the existing wiring? (It is taped together and fairly stiff) Once i determine the line side with my voltage tester i assume i can pigtail the load wires together and connect them to the outlet. What is the best way to pigtail this old wiring? Plastic wire connectors or electrical tape?

Can anyone recommend any books for this type of wiring and repair? I have Rex Cauldwell's book "Wiring a House" but it deals mostly with newer houses and not older houses.

I hope someone can help me out there or is it time to call in a professional electrician?

Thanks for your time.
Old 10-23-03, 09:56 AM
Join Date: Sep 2000
Location: Fayetteville, NY, USA
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I don't think you're at the point where you have to call in a pro yet. You're just replacing receptacles. Most homeowners I know do this themselves with little trouble and get pretty expert after doing the first few.

As far as the third pair of wires, it's possible they are just passing through on their way somewhere else. If they are just taped off but not connected to that receptacle that would be the case. Not able to tell you what they are without a voltage test.

Home Depot sells two Sunset books "Basic Wiring" for $11.65 and "Complete Home Wiring" for $17.95. Borders has a very nice offering for $14.95 from Black & Decker books, called "Basic Wiring & Electrical Repairs". For $16.95 they also have, from Alpha Books, "The Complete Idiot's Guide to Electrical Repair". I've looked through all these and found them to have excellent illustrations and color photos of the work, and good step-by-step instructions.

One thing to note about your recep replacement. The NEC permits replacing 2-prong receps with 3-prong, in an ungrounded system like yours, under one condition. Each new ungrounded 3-prong recep must have a label that says "No Equipment Ground". Most new GFCIs have a set of tiny stickers in the box and I think that's what they say but I forgot because I'm running a ground to all my receps in my 1877 house and threw all my stickers away.

Anyway, this requirement is due to the fact that while you are protected from short circuits, or any leakage from hot to neutral or hot to ground, you are not completely immune from getting a little zing if you're using a grounded tool or appliance with a 3-prong plug and standing in a puddle on your basement floor barefoot! The tool or appliance is not grounded. That's why the warning. Suitably notified of the absent ground anyone plugging into that recep will hopefully use all due precaution. Still, anything more than a little zing and the GFCI will likely trip.

Another thing to note is that if you can determine the very first recep on that circuit (the first one wired from your panel and usually the closest) you can save money by installing a GFCI there and connecting the load side wires to the rest of that circuit. All receps downstream can be regular non-GFCI) 3-prongers and will be GFCI protected by the first one. This is permissible by the NEC and this is why they have a line and a load side. Still, all receps on that circuit are required to have the sticker.

Next thing is terminations and pigtails. First, identify hots & neutrals. I'm guessing the black striped wires are hot but am not sure. Find a reliable ground source and test each wire to ground. Neutral will not give you a reading (0 volts). Now, and I'd guess you know this but I'll say it, hot goes on the brass screws on the recep and neutral goes on the silver screws.

To un-do the pigtails I'd get a firm grip on the insulated part of a group of pigtailed wires with soft-jawed pliers, or fold a small piece of 1/8" rubber or something similar over the insulated part and hold firmly with regular flat-jawed pliers. Now grip the bare twisted-together ends and untwist nice & easy. If you damage that old insulation you're going to have problems. When you go to re-do the pigtails never trust electrical tape alone. Always use wirenuts. Make sure you use the right size too, they're color-coded and the box will tell you how many of what size is permissable. I would guess that in 1935 most if not all of your house wire is #14.

I hope this helps. Let us know how the job worked out for you.


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