My son lives in San Francisco, and would like me to re-wire some of his house. It's pretty old and he says it has knobs and tubes wiring. What is that, and how difficult would it be to replace whatever is there with current outlets, and maybe upgrade his entire electrical service?
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Wayne Watson (Nevada City, CA)
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Knob-and-tube is the oldest style of wiring. Individual wires run between ceramic knob insulators nailed to the framing, and run through ceramic tubes wherever a wire has to go through wood. I don't think any house has been built this way since the 1930's. The only way to upgrade knob-and-tube wiring is to abandon it and run new cable to new outlets and fixtures. If you have access to the attic and a basement or crawlspace, this may be possible without ripping the walls open. If the building still has the original service entrance, that will have to be upgraded to comply with the current electrical code. That's a job for a licensed contractor. Think second mortgage.
It is "Knob and Tube", there are no 's' at the end. It useses single insulated wire, hollow ceramic tubes with a ring at one end. These are used to pass wire through wood studs and beams. The knobs are two piece ceraminc insulators with grooves to hold two wires, and a nail to hold them against a piece of wood.
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Do not attempt to retain any of it. This
Get a pro on site. The wires are likely not the only concern in this most-of-a-century-old stuff.
All, now that I see pictures of this, yes, I've seen this in old historic buildings.
I re-wired a good bit of our house 20 years ago, but it already had modern hardware. I added several new circuits and replaced the circuit box. Of course, I was much more agile then, and this might require some acrobatics to remove all the old stuff.
I think I'll talk to a pro around here before venturing off to SF. We have quite a few historic and just plain old buildings here. Perhaps then following up with a pro in SF might shed some light on the situation there. He lives in essentially row houses, that is, about 20 houses are side by side in a block. Maybe the locals have some ideas about the matter.
I would th> W. Wats>> My son lives in San Francisco, and would like me to re-wire some of his
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Wayne Watson (Nevada City, CA)
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I live in SF too, and have seen a lot of old houses with knob and tube wiring, and owned one, an 1892 Victorian, once. I ripped out all the k+t and replaced it with Romex.
Knob and tube is found almost exclusively in attics and ground-floor garages, so most or all of it should be accessable. It's not hard to rip it out, replace it with Romex, and install new, grounded outlet boxes. People often leave light switches and ceiling lights alone, in situations where the wires are inside walls and the current is low. Just install a junction box to make the romex-to-old-stuff transition.
Longterm, k+t is hazardous, as the junctions were just twisted and taped, not in boxes, and are not able to stand up to modern high-current loads, so become fire hazards.
If the service entrance and fuse/breaker box are not up to modern requirements, you're pretty much faced with hiring electricians and getting permits.
Discount Builders, on Mission street, is a good place to buy stuff, if you don't feel like trekking down to Home Depot.
John
As the knob-and-tube wiring doesn't have the green safety ground wire run to each outlet, simply replacing the existing 2 pin outlets with new 3 pin outlets won't do anything for safety, as there is no way to ground the third pin.
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Wayne Watson (Nevada City, CA)
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Thanks for the local view on the matter.
He's on 47th Street near the zoo. Are Discount Builders anywhere near there? I think there's a HD about 1.5 miles away on Sloat.
It's likely I'll tackle the simple stuff like putting in 3-prong outlets where feasible. I'll provide a ground through pipes or whatever is reasonable.
It probably wouldn't hurt to do an > >
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Wayne Watson (Nevada City, CA)
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Nope, clear across town in the Mission. You may as well go to Home Depot in Colma. Colma is famous for having more dead people than live people.
Yuk! Run some romex; it ain't that hard.
John
That is not acceptable per the National Electrical Code. (See 2005 NEC 110.54 (B) ) It requires that the ground wire (the NEC calls it the Equipment Grounding Conductor) be run in the same metal raceway or jacketed cable (eg Romex) that serves the circuit. You can't ground K&T circuits per the NEC - you need to abandon the K&T and replace the wiring to properly install a grounded circuit. If the service is ungrounded, then it must be replaced before installing grounded branch circuits.
Installing 3-prong receptacles in an ungrounded circuit is another NEC "no-no", but is allowed if the circuit is fed by a GFCI and the receptacles are labeled as not grounded.
Ed
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Wayne Watson (Nevada City, CA)
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Wayne Watson (Nevada City, CA)
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I just Googled, and found this statement, which seems contrary to your statement (see a page or more down at ):
"As you noted...K-N-T never had a ground..so you can NOT legally install 3 prong grounding receptacles on this wiring....to do so is a Code violation...it creates the illusion of a grounded receptacle when there actually is no ground....so if you are installing new receptacle outlets...you MUST install only 2 prong non-grounding receptacles (which are getting harder and harder to come by now-a-days...we had to special order our last batch ) or gut out the obselete K-n-T and run all new 12/2 with ground romex in it's place. As far as new switches...these can still be installed on non-gounding circuits....and there will obviously be no physical connection to the switch's green ground screw. (NOTE: certain light fixtures - especially 2' and 4' flourescents fixtures - may not operate well without a ground in place)
Clearly...to make this mansion electrically safe, functional and up to date...the K-n-T MUST go...and to replace it all at once can be a rather expensive undertaking...perhaps you can do it in small sections...a little at a time. 12/2 w/ground romex can be bought in short 100' and 250' foot rolls...and this may be the approach you need to take."
I would th> Thanks for the information.
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Wayne Watson (Nevada City, CA)
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In a lot if San Francisco, it's so rocky that you'd never get a 6' ground rod very deep. And in most of the rest of the city, the sandy parts, you'd be in dry sand, an excellent insulator. He's only a block from the beach, so he's likely on sand, and it may be dry. It doesn't rain much here, basically not at all from April through October.
Really, do it right, and don't electrocute your descendants.
John
The sand is certainly an interesting angle from the stand point of conductivity. When I go down there, I will check with nearby neighbors, electrical contractors/suppliers and the city engineers to understand what we might be up against.
Another interesting angle on all this was brought up by another poster, or a web site I visited was KnT fixtures may be disappearing. If so, that could spell doom for many of the inhabitants of SF and elsewhere around the country who might need to replace them.
I saw another article that suggests replacement of some fixtures might require > >
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Wayne Watson (Nevada City, CA)
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If SF is like Seattle, if you don't have a ground rod the power panel ground is bonded to your water line.
You'll need to run the ground from the rod to your power panel where it is hooked to the neutral line in the power drop. Otherwise you're relying on the random condutivity between the safety ground and the neutral to blow the fuse if case of a fault. You could end up with stuff live because it didn't blow, or random parts of your house heating up from the stray current.
Also if this is a subpanel off of another box..., well, hire a pro.
(I am not a Lawyer or an Electrician).
Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)
I assume the (my) statement you are referring to is: >>> Installing 3-prong receptacles in an ungrounded circuit >>> is another NEC "no-no", but is allowed if the circuit is fed >>> by a GFCI and the receptacles are labeled as not grounded. >>>
I'm sure you can find all kinds of erroneous statements with Google, but such statements are not the code.
Here is what the 2005 NEC says in 406.3 (D) (3) (c): "A non?grounding-type receptacle(s) shall be permitted to be replaced with a grounding-type receptacle(s) where supplied through a ground-fault circuit interrupter. Grounding-type receptacles supplied through the ground-fault circuit interrupter shall be marked ?GFCI Protected? and ?No Equipment Ground.? An equipment grounding conductor shall not be connected between the grounding-type receptacles."
Actually, it would be a glaringly obvious fail if it was inspected. It violates a large portion of 250.50 - 250.100 (and possibly more) as well as 110.54 (B) That's sure to cause a problem when selling the house, if no inspection is done earlier.
Ed
The US Code calls for a ground rod tie (length specified) in addition to being tied to the power Co, neutral and ground.
I'm talking about old practice, not current code. The code changes. For example, they didn't use plastic pipe in the old days.
The second point is that using a seperate ground and just running that to some outlets is a serious safety hazard.
Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)
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