Extending K&T with ground ?

16 years ago

I'm wondering if extending a K&T circuit by one outlet is okay GIVEN the following: (sorry to be long, but I'm trying to give all the details I can! I'd rather not be like some people on some forums who post incomprehensible details in separate posts days apart...)

- House built 1947. Recently upgraded service to 100A, had 3 different electricians say that's all they would install, though one did say he COULD install 150 if we particularly wanted it. All three thought the condition of the wiring throughout the house was excellent - two from brief inspection, one from the work he did in the house and some poking around with me out of curiosity. I think he was surprised to see a K&T install in such good shape, honestly. There are no cracks, no brittleness, no insulation falling off, no weird splices in dangerous ways (at least none going to any outlet, switch or light fixture - we've had them all open), etc. Even most of the in-wall runs are covered in intact loom, very little of the insulated wire is visible. *Every* new circuit that's been added runs straight back to the box. No circuit is even overloaded, though we did take out one K&T outlet and run a new (secondary) 20A outlet circuit in the kitchen. No, there is no fill-insulation contact in the attic ;) There was an originally-installed ground to the upstairs bathroom outlet (only one with tub/shower in it), but nothing else has a ground that's original to the house. Electrician remarked that if they'd only run those ground wires to all the outlets, he'd say we had the best of both worlds, safety-wise.

The only place there's any significant deterioration at all is in the outlet boxes, where perhaps 1/3 of the wires (which are still for the most part easily visibly white and black) are having some of their middle cloth insulation fray out. Even in those cases, the rubber insulation is 100% intact, and electrician recommended just cutting off the frayed end and taping the remainder down, extending the tape out somewhat over the rubber-only part as well.

Now that the background's out of the way, the subject at hand:

- One outlet on the wall of one room above the garage, which is being used as an office. Circuit is 20A with #12 wire.

- GFCI installed on the relevant outlet (the others too, but that doesn't matter here). This outlet and two pretty-much-never-used outlets are on this circuit. Electrician verified these three outlets are all that's on the circuit. This outlet is the last one - so there are only 2 wires coming in to it, nothing else.

Yes, I know I don't really need GFCI in an office on a grounded circuit; it's not against code and it's not hurting anything though... I put in GFCI's elsewhere in the house for people-protection due to lack of equipment ground. Yes, I'm aware a GFCI is not equal to an equipment ground, but it's safer than a plain 2-wire outlet! We did install a whole-house surge suppressor at the panel which hopefully will help with equipment-protection in a middling-catastrophic situation - I have no illusions about a lightning strike :)

- This outlet is accessible easily from behind in an eave storage space, due to an easily-removed section of drywall that's not painted or anything - but it is an enclosed space surrounding the studs once the drywall is nailed back into place. Obviously we can only remove it so many times, but we're confident it will survive being put back up after we decide what to do here.

- There is a #12 ground wire there that someone pulled through from below, I'm guessing in the last 10-15 years or so. It's grounding the one outlet here that I'm concerned with. It does not go over to the hallway outlets. I haven't the foggiest idea why it was only run to this one outlet. I have verified this ground does, in fact, run back to the box properly.

What I want to do is: Run 12/2 with ground from the load side of the GFCI (no direct connection to the old wire, just run off the outlet.) Pigtailing at every outlet is not required in my locality. I will, however, obviously pigtail the ground wire to the ground of the GFCI. Then, about 4-5 feet down, I want to install another outlet using the standard 12/2 with ground connection, just as I would for an all-new circuit. If you're wondering, the idea is to get an outlet beyond a very heavy desk that will only go one way ;)

I realize I can pull all new wire up using the existing ground wire as a guide; however, it's attached in some ways that I can't imagine how they got to the wire to attach it. I'm speculating that at one point a wall on the first floor was open, allowing this wire to be attached easily - also, it's not a clear drop to the basement. No fishing with a golf ball here, sadly!

The only reason I'm even considering this is that this circuit is grossly under-loaded, the wire is all in good shape, and I can make a direct box-to-box connection (with the exception of the pigtail ground, which isn't a concern). Since I'm running a ground with it, I'm thinking this should be okay, but wanted to get some advice prior to actually starting to drill holes (of the proper size, in the proper locations, never fear!) in studs.

Sorry to ramble on; any thoughts? I may post this elsewhere to maximize response, so don't get peeved if you read it more than one place ;)

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Comments (13)

Ron Natalie
16 years ago
The GFCI (given proper marking of the downstream receptacles) make the use of those three prong receptacles with no legitimate ground connection legal.

In addition the ground wire, provided it goes back to the panel (or the grounding electrode system) is also Ok to ground these circuit extension. I assume you have verified it goes back to the main ground bar in the service panel (you just said box without qualifying it). It can't just go to some random water pipe or other circuit box.
thewgp
Original Author
16 years ago
last modified: 9 years ago
Ack, I knew I'd forget some detail! The wire does go back to the actual bus bar in the main (only) panel. Further, nothing is doubled up in there, it's a brand-new install. The electrician pointed this wire out to me, said he saw a ground wire going *somewhere* but couldn't tell where - I'm the one who figured out where it went, and he then verified at a later time that it was the same wire. We really just can't figure out why they only ran ground, and didn't just run a whole new wire up there at the same time when they probably had the walls open.

I know the GFCI's are OK by code to install on K&T for 3-prong if they're labeled no equipment ground - we're doing that in selected locations throughout the house for just that purpose - but what I'm wondering is if the actual extension of the circuit is okay, or am I absolutely positively supposed to run a new wire all the way back? I know a lot of people advocate that, but the way I'm reading the Code, I don't think that's neccessary - only the ground wire seems to be required to extend the circuit out legally. Or do I even need that, so long as I'm using only GFCI's?
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Ron Natalie
16 years ago
Yes, since the wire goes back to a permitted ground (the panel), then you can use it to ground extensions to ungrounded circuits. The applicable part of the NEC is 250.130(C):
The equipment grounding conductor of a grounding type receptacle or branch circuit extension shall be permitted to be connected to any of the following ... (3) The equipment grounding terminal bar within the enclosure where the branch circuit originates.

Note the "OR" in that statement. You can use that wire to ground the single receptacle (what you have now) OR your extension (what you intend to do).
thewgp
Original Author
16 years ago
last modified: 9 years ago
Okay, great - hmm, I am wondering why it can't be used to ground both outlets, though. I'm reading that sentence as "a ground wire coming from (these sources) is permitted to be grounded to (the ground bar in the main panel). That is, I thought 250.130(c) primarily dealt with where it's OK to ground to, ie, the whole grounding-to-a-water-pipe debate that I don't want to get into, but you know what I mean.

Certainly, if I was installing an all-new circuit, that's how I'd do it - pigtail into each outlet - so I'm not 100% sure why that's not OK here?

It's fine if it really isn't okay - I'm only REALLY going to be using one of these outlets, but since they're so close and it would be so easy to connect both outlets to this ground wire, it's tempting, for future flexibility. Definitely since I don't think we have any real means of getting a new ground wire up to the second floor, at least until we maybe gut the bathroom! :)

I'm going to go ahead and drill my holes in the studs and knock out the spot for the outlet, at least. It's exciting to get some progress!
Ron Natalie
16 years ago
It can be used for both. The or is inclusive.
electric_medic
16 years ago
last modified: 9 years ago
You can go to an existing circuit which is only a two-wire, non-grounded circuit, and add a receptacle to it with 12-2 with ground, coming from the load side of a GFCI, and consider it legally grounded. The GFCI does simulate the effect of a ground (even with NO ground wire run to the panel as in your own situation), and may feed to three-prong grounded outlets with 12-2 with ground. Adding outlets to the circuit is contingent only upon the load demand of the circuit, and if you know you are not exceeding 16 amps on a 20-amp circuit with lighting or some other continuous load, you may always add on to an existing circuit. No problem - go ahead in good health.

David Moore
Electric Medic
Oak Ridge and Knoxville, TN
http://electricmedic-tn.com
normel
16 years ago
last modified: 9 years ago
Extending a non-grounded circuit using 12/2 with ground by attaching to the load side of a GFCI does NOT make it a grounded circuit nor does it simulate a ground. You may use grounded receptacles on such an extension, but they must be labeled as "No Equipment Ground" and the grounding conductor must NOT be attached to the GFCI or downstream receptacles. See NEC 406.3 (D)(3) (b&c).
Ron Natalie
16 years ago
Normel is right.

However, the original poster has a ground wire run to feed the ground terminal on the circuit extension. He can use that to provide the ground (and intends to). Whether he choses to use the GFCI or not is purely up to him at this point. No receptacle labelling is required in this case.
thewgp
Original Author
16 years ago
last modified: 9 years ago
Yeah, I'm actually just about finished with this install - all that's left is to replace the drywall in the access space. Good to know that we're safe and legal!

Question, though: Why is it that a normal 3-prong outlet is OK to run off a GFCI load-side even in the absence of ground?

I understand it's functionally equivalent to just installing a GFCI there, but those little stickers may fall off over time, etc! Just seems so likely to confuse someone down the road, even though it's code legal. They could certainly assume there's an equipment ground there when there isn't, even though a person would (if all works as designed) be protected by the GFCI earlier in the circuit.
DavidR
16 years ago
last modified: 9 years ago
I've wondered the same thing. I had some work done on one of my rental houses a while back, GFIs putin the kitchen where the old wiring wasn't grounded. Stickers went on the downstream recepts. Tenants moved out last summer and when I went in to inspect I noticed that they'd peeled the "GFI Protected, No Equipment Ground" labels off all the recepts.

Maybe one day the code will require cover plates with that text embossed on them.
Ron Natalie
16 years ago
Because as far as life safety is concerned the GFCI does as good (or not better) than what the equipment ground provides in that case. It sucks for things that really wanted a ground (like a surge strip but the code doesn't much care about that).
brickeyee
16 years ago
last modified: 9 years ago
"It sucks for things that really wanted a ground (like a surge strip but the code doesn't much care about that)."

And some surge strips actually 'leak' enough current to trip a GFCI.
Ron Natalie
16 years ago
> And some surge strips actually 'leak' enough current to trip a GFCI.
Then they need to be replaced. Nothing in the surge strip should cause a ground fault. If the MOV is leaking, it's probably not protecting either.

Extending K&T with ground ?

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Extending K&T *with ground* ?

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