Ungrounded wire on new grounded circuit

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Old 07-21-12, 08:41 AM
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Ungrounded wire on new grounded circuit

I apologize in advance if this has been dealt with elsewhere - I haven't found a relevant thread.

I'm rewiring a 19th-century home filled with knob and tube. I've replaced all but one run: an old 2-wire, no ground, from a switch to a light fixture. It would be very difficult to get into the framing to replace that wire, so I'm wondering if there's a work-around for getting any protection on that switch-fixture run.

I've heard talk of feeding the switch from a GFCI receptacle. I could do that on one of the new circuits (20A circuit with every other switch and receptacle on the circuit being wired with grounded 12-2 or 12-3). Is there anything to that idea? Thanks.
 
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Old 07-21-12, 09:26 AM
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It would be very difficult to get into the framing to replace that wire
Maybe I'm interpreting what you wrote too strictly but to be clear they do not need to be replaced. They can be abandoned in place and power run from a different direction or in a different manner. Perhaps with more details we can help you to properly replace this last section of K&T.
 
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Old 07-21-12, 10:50 AM
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My interpretation of the problem is that it would be difficult to rewire that run from the switch to the light fixture. And the OP is concerned about the fixture having a ground wire on it and not being able to connect it to the rest of the system.
 
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Old 07-21-12, 12:10 PM
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drooplug,

You're right. I can't run new wire from the switch to the light without more demo than I have time for. My concern is how to mitigate having only a hot and a neutral from the switch to the light, since I can run grounded cable to the switch only.

I am running new lines in parallel (roughly) with the old, and I'll abandon the old lines in place once I make the final switch-over at the panel.
 
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Old 07-21-12, 12:19 PM
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Is this on the first floor of a two story house with no crawl space or basement below and not on an outside wall? Is that why you say more demo? Have you considered a wireless switch or surface race?
 
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Old 07-21-12, 12:43 PM
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The light is a hallway ceiling fixture on the 1st floor of a 2-story. I can run a feed to the wall switch from the basement but can't run a wire up from the switch, through the top plate, and over to the fixture - I really battened down the flooring right over that wall and fixture and would like to avoid ripping into it again.

I suppose I could run a surface race or install wireless but am curious about other options. I've heard that feeding an ungrounded device from a GFCI outlet at least allowed for protection against electrocution at that device, since the GFCI would trip if there were an imbalance between the hot and neutral. Any ideas?
 
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Old 07-21-12, 01:28 PM
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If power comes in at the switch you could use a GFCI switch/receptacle combo or replace the single gang box with a double gang box and use a dead face GFCI and your switch. I write this with reservation because we are in murky waters doing things not normally done. Probably simplest is just to leave it ungrounded.

Problem number two you haven't mentioned is that if it is K&T at the light you have 60 wire and most modern light fixtures require 90 wire.
 
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Old 07-21-12, 01:39 PM
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I know it seems like a pain, but considering it sounds like you've gone to the pains of removing all the other K&T throughout the house, wouldn't it be nice to say to your insurance company, next homeowners, etc. that there's no K&T in the house?

To the pros, would it be code to use MC wire and notch the drywall/plaster around the top plate? Or use a metal nailing plate? That would just leave a little strip to re-plaster as opposed to a full cut-out?
 
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Old 07-21-12, 02:24 PM
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I'm rewiring a 19th-century home filled with knob and tube. I've replaced all but one run: an old 2-wire, no ground, from a switch to a light fixture... My concern is how to mitigate having only a hot and a neutral from the switch to the light, since I can run grounded cable to the switch only.
It can be permissible to leave good K&T in place and using it. Do these wires appear to be in good condition? If so, check with your permitting authority.

To do that, you will need to use an old work metal box with internal clamps. Wrap each leg of the K&T with a few wraps of friction tape where it will enter the box, and clamp it firmly but gently. Determine which leg is, or will be, the neutral. Bond the box and the switch to the ground in your new feed cable, splice the neutrals and switch the hots.

At the fixture, how is it mounted? If your house originally had dual-fuel lighting, and the fixture was suspended from a now-abandoned gas pipe, bond that pipe system to ground in the basement - or wherever you have access to the grounding electrode conductor - and check for continuity from the pipe in the ceiling to a known good ground nearby.

If you get it, make sure your new metal ceiling box is in good contact with the pipe and attach the fixture ground to that. If not, oh well. Make sure that the outer shell of the lampholders (sockets) in your new fixture are connected to neutral, in either case.

Note:60[SUP]o[/SUP] C. wire can serve a pendant light, but not a tight-fitted fixture. I'm guessing the new fixture will be a pendant style, but mark the new box with that instruction as a precaution.
 
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Old 07-21-12, 02:26 PM
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Is the floor above carpeted? If so I'm not seeing any reason for a major tear out especially if the cable run would be parallel to the joists. Judicious use of a hole saw in two or three places to make hand openings easily plugged afterward and hid by carpet would be enough.
 
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Old 07-21-12, 07:22 PM
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Hey Nash, slightly off topic, but what if the OP had a similar problem at a full masonry outside wall where the K&T was in the masonry to both receptacles, switches and, let's say, outside lights at the front door. What would you do then?
 
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Old 07-21-12, 07:32 PM
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#offtopix# CasualJoe, I actually had that situation. Ended up running conduit down an outside wall from the attic. But it was a rental so aesthetics wasn't a primary concern.
 
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Old 07-21-12, 07:41 PM
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But it was a rental so aesthetics wasn't a primary concern.
Quick answer Ray, ty for that. Ok, suppose aesthetics is a concern, what then? Still looking for other opinions on this too. I have been avoiding giving an answer to this very question for a while.
 
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Old 07-21-12, 07:58 PM
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I'm leaning towards what Nashkat is proposing but I want some more info.

Is the light fixture currently, or in the past supplied by power going FIRST to the switch and then to the fixture or is it as most light fixtures of that era supplied with power at the fixture and then a switch loop to the switch?

Is this lamp fixture close-hauled to the ceiling (a ceiling mount) or is it a pendant fixture?

What is the physical condition of the insulation on the wire where it can be inspected?

What size of light bulb has been used in this fixture over the years and what size wire is installed?

Can a CFL or LED lamp bulb be substituted for the incandescent bulb now being used?
 
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Old 07-21-12, 08:57 PM
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replies and more info

ray2047,
If it were carpet, I'd do what you mentioned in a heartbeat. I've ripped out all the carpet, repaired the antique heart pine, and socked it down everywhere. It won't come up again without a lot of damage. Thanks for the suggestion, though.


Nashkat1,
Thanks for the info. Unfortunately there's no grounding medium near the ceiling box. I can do everything else you suggested, though. Any benefit to feeding the switch from a nearby GFCI?

Furd,
Power is fed to the switch; the fixture is close-hauled, but I'll replace it with a pendant; the few inches of insulation I can see at the switch box and ceiling box are alright; 60W bulb, 14g wire; bulb substitutions are possible. Thanks.
 
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Old 07-21-12, 09:07 PM
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I wouldn't worry about it. As long as the insulation that is visible isn't seriously decayed (it doesn't sound like it) the rest of the insulation is probably in at least as good of condition. This has ALWAYS been my observation when looking at old rubber and cloth insulated wire. Even when the ends in the boxes is crumbly the rest is often in excellent shape, especially when it was in conduit, which I realize this particular case is not in conduit.

A 60 watt lamp draws about 1/2 ampere and on #14 conductors that is NOTHING! Even if the conductors were #16 (once used in residential lighting) it would STILL be nothing. It is high currents that heat the conductor that destroys rubber and fabric insulation.

I would ground the (metal) switch box or switch with the new cable and forget the rest. Using either CFL or LED lighting would reduce the already low current flow even more.
 
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Old 07-21-12, 09:13 PM
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CasualJoe: We ran coated MC in channels we cut in the brick on one job to deal with that. This was in an old 1770s mansion that is now the main building of a high-end private school, so aesthetics was a high priority. We could, and did, tear out anything that was in the way. We just had to invisibly replace it later.
 

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Old 07-21-12, 09:20 PM
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I've ripped out all the carpet, repaired the antique heart pine, and socked it down everywhere.
Sounds beautiful.

Any benefit to feeding the switch from a nearby GFCI?
None that I can think of, and there might be some drawbacks with using, for example, CFLs.

the fixture is close-hauled, but I'll replace it with a pendant; the few inches of insulation I can see at the switch box and ceiling box are alright; 60W bulb, 14g wire; bulb substitutions are possible.
I'd put a 60W-equivalent in there until I got the pendant fixture installed.
 
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