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Discussion Starter #1
Let me explain: I'm trying to add GFCI protection to the basement outlets in my father's house, which was built in 1961. Most of the wiring is original, and is in pretty good shape. Although there is no ground wire, the entire house is snaked with 1/2 inch flexible metallic conduit, which serves as the ground conductor throughout.

The basement circuit I'm trying to protect serves lighting and outlets in a completely finished portion of the basement. The outlet closest to the breaker panel is served by a 14 ga. black and white pair ran through 1/2 inch flexible conduit which drops from a ceiling box in a utility room, down to the outlet. Nothing else continues off of that outlet.

The rest of the outlets and lights are served via other branches exiting the same ceiling box.

I'd like to add another black and white pair to that first outlet branch so that I can protect that outlet and the rest of the circuit through a single GFCI receptacle. (Actually, I'll just pull 4 new wires, using the two old ones to pull the four new ones through the flexible conduit--that way, I don't need to worry about damaging the 48 year-old insulation pulling new conductors right next to the old.) Since it's in an unfinished area, I'm planning to use a box extender on the ceiling box so that I can fit 10 conductors in there instead of the 8 that are in there now, and have it stay up to code.

Does this plan sound good? Is it OK to use white for both the load side and line side neutrals (I was going to use black and red for the load and line side hots), or do I need to use a different color, or reidentify it somehow?

Or is it out of the question? (In which case, because of how I reckon the circuit is laid out, I'd have to use 5 GFCIs instead of just one to protect 9 outlets, because busting open walls in this house is not going to happen.)
 

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Yes you can use white for all neutrals, line and load sides of GFCI's included. I think light gray is a permissible color for neutrals but for the home DIY'er it's just an added expense for a supply of that color wire.

You may use black for both line hot and load hot. It is also permissible to mark black wires with red, blue, etc. (any color except white or green) tape at both ends for identification purposes if you wish.

Yes you may run the line neutral (and hot) out the single conduit from a junction box to the GFCI receptacle and the load neutral (and hot) back in the same conduit to the junction box (and off in a different direction from there) if that is the way the conduits were strung.

Double check to be sure this is 1/2 inch flexible conduit with individually strung wires as opposed to pre-made metal sheathed cables. The latter may have a paper lining inside the "conduit" occupying too much of the cross sectional area to allow 4 new wires.
 

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Also, while it may be adequately grounded by the metal flex, it is technically not a code compliant grounding method. Metal flex over 6 feet long is not an approved grounding means, not even in the 60's. This is not to say that it won't work, however. If I were working on this, every box that I disturbed, I would tighten the conduit connection, just to be on the safe side.
 

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If you have a bonding strip (thin aluminum or copper wire) the jacket can serve as the ground. Tighten the box clamp, in the 60s they left them loose sometimes.
 

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Maybe I've been living a parochial existance, but I have never seen 1/2" flexible tubing!
BX cable cable, yes!
If its important to have GFCI on the circuit, why not install a GFCI breaker in the panel and be done with it. If the breaker is too expensive, a GFCI receptical could be installed at the electrical panel and the circuit fed down-stream from this!
 

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Here is what FMC looks like:

http://www.amazon.com/dp/B000HEKU9A...e=380337&creativeASIN=B000HEKU9A&linkCode=asn

FMC was required in CA and still may be reguired in other areas like EMT is required in Chicago. It is still at all the supply houses here and is still popular because it makes electrical modifications easier. It comes in aluminum or steel with a whole range of fitting to connect to EMT or rigid.

1/2" FMC is rated for nine 12AWG conductors so adding capacity to an existing run can frequently be done without tearing open the walls.
 

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Maybe I've been living a parochial existance, but I have never seen 1/2" flexible tubing!
BX cable cable, yes!
If its important to have GFCI on the circuit, why not install a GFCI breaker in the panel and be done with it. If the breaker is too expensive, a GFCI receptical could be installed at the electrical panel and the circuit fed down-stream from this!

Dang guy, you ought to see 4" fmc.

thegonagle: you need to check to see how many additional recpetacles you can feed from the GFCI device you have. It seems most I have used limit it to 4 or 5. Your post inferred you were intending on putting 9 receps on the one GFCI.


You should also check state or local code as to the need for an EGC. NEC does not require one in the manner of use you have but Michigan does. I don't know what Minn requires. Never hurts to have one though.
 

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Nap is right on the egc (Equipment Grounding Conductor) When I moved into my 1954 house in 84 I found a 2400 sq ft FMC wired house that was fed by a six breaker panel with NO main. On the first box that I opened I found a two prong double D receptacle connected with a green and a white 14awg TW wire. When the house was built in 1954, green was an acceptable color for a conductor. I'm sure that there are still some houses here that have the same set-up.

It took almost a year to get everything replaced, moved the meter, up'd the service to 200 Amp (& moved it away from the meter) added two 70 amp SquareD load centers with a total of 54 breakers. I tore out every piece of the 60°C TW and pulled in almost every possible color of 90 °C all 12AWG THHN. Every run had a green 12AWG EGC. I really did an overkill by making most of the breakers Square D GFCI's. Thank God this was before AF or I would have gone down that road.

I had to add some runs and also used some EMT and a little NMB. I had to because I was maxed out, on a few runs, on the conduit fill at 13, 12AWG wires (that was legal in the mid 80's) The whole thing was still overkill in a California house with all gas appliances and No AC, but it was fun. On the day of the inspection the inspector found one problem, an open box that had the last little unconnected unused piece of the old green TW. He solemnly told me "Remember, Green is Ground".
 

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One thing you should be aware of is that according to Table 310.15(B)(2)(a) of the NEC, the ampacity of the wire must be derated if there are four current carrying conductors. The permitted ampacity for this line is now 80% of the rated 15 amps, i.e. 13 amps is now the max permitted draw through this line.
 

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One thing you should be aware of is that according to Table 310.15(B)(2)(a) of the NEC, the ampacity of the wire must be derated if there are four current carrying conductors. The permitted ampacity for this line is now 80% of the rated 15 amps, i.e. 13 amps is now the max permitted draw through this line.
Sorta! It should be derated 80% of the max ampacity of the wire, not the circuit.
If the wire is 14 thhn/thwn then the ampacity is 25 amps, so you can still put the wire on a 15 amp breaker.
 

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Sorta! It should be derated 80% of the max ampacity of the wire, not the circuit.
If the wire is 14 thhn/thwn then the ampacity is 20 amps, so you can still put the wire on a 15 amp breaker.
I believe you are mistaken, as Table B.310.1 states:

*Unless otherwise specifically permitted elsewhere in this Code, the overcurrent protection for these conductor types shall not exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG, and 30 amperes for 10 AWG copper; or 15 amperes for 12 AWG and 25 AWG amperes for 10 AWG aluminum and copper-clad aluminum.
 

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True, but for derating you use the max ampacity of the wire, not the max breaker size.
 

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True, but for derating you use the max ampacity of the wire, not the max breaker size.
That's an interesting point. I'll have to ask around at work tomorrow about that one. I was always under the impression that for derating purposes (conduit fill) the permitted overcurrent ampacity was used to calculate the derating, not the maximum theoretical ampacity of the wire. I don't have my Ugly's with me, but I doubt that the theoretical ampacity of 14 guage wire in FMC is 20 amps, since it's free air ampacity is 18.
 

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So basically even with the derating based on the ampacity of the wire the 15a 14g & 20a 12g wire

is OK

Even at 18 = 14.4 derated & my understanding you can round up...no?

25 = 20 derated...
 

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Discussion Starter #20 (Edited)
The circuit already has "too many" things on it, but that's how it was when I found it. I'm just trying to give it an added margin of safety. Realistically, there's a 32 inch CRT TV, a Playstation 2, a digital cable box, a DVD player, 5 CFL light bulbs, two incandescent table lamps, and a Pentium 4 setup with an inkjet, an external harddrive, 19 inch LCD, cable modem, and a wireless router running on the circuit. There's never been an issue, so I'm leaving well enough alone. If in the future that becomes inadequate, we'll cross that bridge when we arrive at it.

My father and step mother purchased the home in 2005. I'm not sure how the house would have passed the rough-in inspection all those years ago without the grounding conductor if it wasn't up to code when it was built. However, code or not, it's built and has been like this for 48 years.

The reason I'm working on this house is because they want to replace all of the two prong outlets with three prong outlets. At most of the outlets in the house, using an analog meter with the respective circuit off, I get about 1-3 ohms of resistance between the box and the neutral. There's no bonding wire or strip that I can see, but the clamps are all still tight. (There have been a few other issues that I've found and fixed as I go along--basically, anywhere a certain clod of a previous homeowner messed with the system, something was bound to have been done wrong. Anything that appears original is really in great shape.)

It's not using BX armored cable, it's definitely flexible conduit. The outer diameter of the stuff is about 3/4 inches, which lead me to believe that it is 1/2-inch internal diameter flexible conduit.

I already put the four 14 ga. conductors in this morning, based on advice that the layout and colors were acceptable. If I'd need to derate to 13 amps, that's not good. Would replacing the four 14 ga conductors in that particular conduit with 12 ga. solve that issue? Now, the 14 ga. was not too hard to pull, but 12 ga. might be, because it curves over 180 degrees total (maybe 210 degrees, the way the flex lays).
 
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