Working with Knobs and Tubes Electrical Installations

[W. Watson]

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?

 

[Stephen J. Rush]

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?

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.

 

[Michael A. Terrell]

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?

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.

<http://www.google.com/search?hl=en&q=knob+and+tube+wiring>


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[JeffM]

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.

Do not attempt to retain any of it.
This
http://www.google.com/images?q=Knob-and-tube
will be replaced with this
http://www.google.com/images?q=Romex-staples+OR+Romex-staple
If you can get the old stuff outm preserve it for a museum.

Get a pro on site. The wires are likely not the only concern
in this most-of-a-century-old stuff.

 

[W. Watson]

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 think at a minimum his house could be helped by putting in new three
prong grounded sockets.

 

[John Larkin]

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?

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.

http://www.oldhouseweb.com/stories/Detailed/10327.shtml


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

 

[Peter Bennett]

I would think at a minimum his house could be helped by putting in new three
prong grounded sockets.

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.



--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

 

[W. Watson]

It's certainly easy enough to run a third wire to a pipe. At worst, I can
drive copper pipe into the ground outside the house and bring it in where
needed.

 

[W. Watson]

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 inspection of the electrical to see if it
could now be considered hazardous. I remember years ago just before I did a
good bit of electrical work on our last house in Mtn. View that a wire had
worn thing. The lights were dimming in the kitchen. I took out the cover
from a switch, and noticed a red glow on a wire. Cute. Apparently the wire
had gotten kinked at some time in the past.

 

[John Larkin]

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.

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.

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.

Yuk! Run some romex; it ain't that hard.


John

 

[ehsjr]

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.

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

 

[W. Watson]

Well, I certainly know where that is. I was there about 2 months ago helping
my daughter buy a computer. It was the only Best Buy store that had a few
left on a weekend sale. That must be where the national cemetery is located.

 

[W. Watson]

Thanks for the information.

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

 

[W. Watson]

I just Googled, and found this statement, which seems contrary to your
statement (see a page or more down at
<http://en.allexperts.com/q/Electrical-Wiring-Home-1734/Old-Knob-Tube.htm>):

"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 think if installed a 6' copper ground bar into the soil outside his
house, and use 3-prong outlets where the ground wire is to the copper pole,
that it would pass code.

 

[John Larkin]

I just Googled, and found this statement, which seems contrary to your
statement (see a page or more down at
<http://en.allexperts.com/q/Electrical-Wiring-Home-1734/Old-Knob-Tube.htm>):

"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 think if installed a 6' copper ground bar into the soil outside his
house, and use 3-prong outlets where the ground wire is to the copper pole,
that it would pass code.

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

 

[W. Watson]

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 opening walls. Yikes! Well, I'll know more when I actually see what
he's got.

 

[Mark Zenier]

I would think if installed a 6' copper ground bar into the soil outside his
house, and use 3-prong outlets where the ground wire is to the copper pole,
that it would pass code.

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 [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)

 

[ehsjr]

I just Googled, and found this statement, which seems contrary to your
statement (see a page or more down at
<http://en.allexperts.com/q/Electrical-Wiring-Home-1734/Old-Knob-Tube.htm>):

I assume the (my) statement you are referring to is:

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."

"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 think if installed a 6' copper ground bar into the soil outside
his house, and use 3-prong outlets where the ground wire is to the
copper pole, that it would pass code.

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

 

[Don Bowey]

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 [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)

The US Code calls for a ground rod tie (length specified) in addition to
being tied to the power Co, neutral and ground.

 

[Mark Zenier]

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 [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)