Ungrounded wire on new grounded circuit


  #1  
Old 07-21-12, 07:41 AM
M
Member
Thread Starter
Join Date: Jul 2012
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
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.
 
  #2  
Old 07-21-12, 08:26 AM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 29,711
Upvotes: 0
Received 15 Upvotes on 13 Posts
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.
 
  #3  
Old 07-21-12, 09:50 AM
D
Member
Join Date: Aug 2009
Location: USA
Posts: 4,344
Upvotes: 0
Received 1 Upvote on 1 Post
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.
 
  #4  
Old 07-21-12, 11:10 AM
M
Member
Thread Starter
Join Date: Jul 2012
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
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.
 
  #5  
Old 07-21-12, 11:19 AM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 29,711
Upvotes: 0
Received 15 Upvotes on 13 Posts
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?
 
  #6  
Old 07-21-12, 11:43 AM
M
Member
Thread Starter
Join Date: Jul 2012
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
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?
 
  #7  
Old 07-21-12, 12:28 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 29,711
Upvotes: 0
Received 15 Upvotes on 13 Posts
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.
 
  #8  
Old 07-21-12, 12:39 PM
Z
Forum Topic Moderator
Join Date: Sep 2005
Location: USA
Posts: 6,095
Received 422 Upvotes on 375 Posts
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?
 
  #9  
Old 07-21-12, 01:24 PM
Nashkat1's Avatar
Member
Join Date: Mar 2012
Location: USA
Posts: 7,458
Upvotes: 0
Received 6 Upvotes on 5 Posts
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.
 
  #10  
Old 07-21-12, 01:26 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 29,711
Upvotes: 0
Received 15 Upvotes on 13 Posts
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.
 
  #11  
Old 07-21-12, 06:22 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: United States
Posts: 9,871
Received 185 Upvotes on 166 Posts
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?
 
  #12  
Old 07-21-12, 06:32 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 29,711
Upvotes: 0
Received 15 Upvotes on 13 Posts
#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.
 
  #13  
Old 07-21-12, 06:41 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: United States
Posts: 9,871
Received 185 Upvotes on 166 Posts
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.
 
  #14  
Old 07-21-12, 06:58 PM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 16,321
Received 38 Upvotes on 30 Posts
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?
 
  #15  
Old 07-21-12, 07:57 PM
M
Member
Thread Starter
Join Date: Jul 2012
Posts: 4
Upvotes: 0
Received 0 Upvotes on 0 Posts
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.
 
  #16  
Old 07-21-12, 08:07 PM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 16,321
Received 38 Upvotes on 30 Posts
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.
 
  #17  
Old 07-21-12, 08:13 PM
Nashkat1's Avatar
Member
Join Date: Mar 2012
Location: USA
Posts: 7,458
Upvotes: 0
Received 6 Upvotes on 5 Posts
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.
 

Last edited by ray2047; 07-22-12 at 03:24 AM. Reason: x>c in smiely
  #18  
Old 07-21-12, 08:20 PM
Nashkat1's Avatar
Member
Join Date: Mar 2012
Location: USA
Posts: 7,458
Upvotes: 0
Received 6 Upvotes on 5 Posts
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.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: