I have an electrician coming tomorrow to look at my newly aquired old
house which has some knob & tube in it that I have to update for
insurance purposes. The home inspector showed me how it's only the old
lighting that now uses the knob & tube, all other electrical has been
The electrician said on the phone that it's possible that he can just
add GFCIs to each knob & tube circuit to satisfy the insurance people.
This will avoid having to rip plaster walls apart.
Is this an accepted way to resolve the knob & tube issue?
Actually, K&T wiring is pretty good stuff!
It's reasonably safe even AFTER the mice have eaten the insulation as the
"real" insulation is provided by the knobs and tubes.
A GFCI on a K&T circuit would protect the circuit from any significant
leakage to ground. The basic nature of K&T is that "shorts" between the
two conductors are very unlikely but anything from a nail going to far into
the wall to a broken insulator might cause contract between a conductor and
some other metal object.
Obviously, you have to do whatever the local authorities and the insurance
company demand but when it comes to REAL safety, a GFCI will do the job.
Just don't forget to TEST the GFCI once a month or so.
If your GFCI doesn't reset, you may have to tear up the walls anyway but the
most likely place for problems is at switches, fixtures, and where you
transition from "modern" wiring to the K&T.
I was thinking the same thing.......
Why would GFIs do much of anything on lights?
K&T was always a durable means of wiring, and lights really do not
need a ground, whereas outlets do. If the K&T is in good condition, I
dont see where it needs anything. Lights dont draw any heavy loads.
But inspectors and insurance people generally dont make much sense
anyhow.... I'd still like to find even one of them that actually
knows how to use a screwdriver.......
On Thu, 10 Aug 2006 18:18:37 -0400, "RBM" <rbm2(remove
local question for your electrical permit office.
you may first want arc fault main panel protection for your antique
also partly quoted below:
"Subject: What is this weird stuff? Old style wiring
In the years since Edison "invented" electricity, several different
wiring "styles" have come and gone. When you buy an older home you
may encounter some of this stuff. This section describes the old
methods, and some of their idiosyncrasies.
The oldest wiring system you're likely to encounter is called
"knob and tube" (K&T). It is made up of individual conductors with
a cloth insulation. The wires are run along side structural
members (eg: joists or studs) using ceramic stand-offs (knobs).
Wire is run through structural members using ceramic tubes.
were made by twisting the wire together, soldering, and wrapping
with tape. Since the hot and neutral were run separately,
the wiring tends to be rather confusing. A neutral often runs
down the centre of each room, with "taps" off to each fixture.
The hot wire tended to run from one fixture to the next. In some
cases K&T isn't colour-coded, so the neutral is often the same
colour as the hot wires.
You'll see K&T in homes built as late as the 40's.
Comments on K&T:
- the people installing K&T were pretty paranoid about
electricity, so the workmanship tends to be pretty good.
- The wire, insulation and insulators tend to stand up
very well. Most K&T I've seen, for example, is in
quite good condition.
- No grounding. Grounding is usually difficult to install.
- boxes are small. Receptacle replacement (particularly with
GFCI) can be difficult. No bushing on boxes either,
so wiring changes need special attention to box entry.
- Sometimes the neutral isn't balanced very well between
separately hot circuits, so it is sometimes possible to
overload the neutral without exceeding the fusing on
- In DC days it was common to fuse both sides, and no
harm was done. In fact, it was probably a Good Thing.
The practise apparently carried over to K&T where
you may find fused neutrals. This is a very bad
- Building code does not usually permit insulation in
walls or ceilings that contains K&T. Some jurisdictions
will allow it under some circumstances (eg: engineer's
- Connection to existing K&T from new circuits can be
tricky. Consult your inspector.
- Modern wiring practice requires considerably more
outlets to be installed than K&T systems did.
Since K&T tends to be in pretty decent condition it generally
isn't necessary to replace it simply because it's K&T. What
you should watch out for is renovations that have interfered
with it and be cautious about circuit loading. In many cases
it's perfectly reasonable to leave existing K&T alone, and add
new fixtures on new circuits using modern techniques.
After K&T, they invented multi-conductor cable. The first type
you will see is roughly a cloth and varnish insulation. It
looks much like the romex cable of the last decade or two.
This stuff was used in the 40's and 50's. Again, no grounding
conductor. It was installed much like modern wiring. Its
major drawback is that this type of insulation embrittles.
We've seen whole systems where the insulation would fracture
and fall off at a touch. BX cable of the same vintage has
similar problems. It is possible for the hot conductor to
short out to the cable jacket. Since the jacket is rusted, it
no longer presents a low resistance return path for the current
flow, but rather more acts like a resistance heater. In
extreme cases the cable jacket will become red hot without
blowing the fuse or circuit breaker. The best thing to do with
old style BX is to replace it with modern cable whenever it's
encountered and there's any hint of the sheath rusting.
This stuff is very fragile, and becomes rather hazardous if the
wires become bare. This wiring should be left untouched as
much as possible - whenever an opportunity arises, replace it.
A simple receptacle or switch replacement can turn into a
several hour long frustrating fight with electrical tape or
After this wiring technique, the more modern romex was
invented. It's almost a asphalt impregnated cloth. Often a
bit sticky. This stuff stands up reasonably well and doesn't
present a hazard and is reasonably easy to work with. It does
not need to be replaced - it should be considered as safe as
the "modern" stuff - thermoplastic insulation wire. Just don't
abuse it too much."
"There are many homes dating back to the 1920's that still have
knob-and-tube that has outlasted subsequent wiring technology, such as
BX with rubber insulated conductors and early forms of romex. Do AFCI
breakers protect existing knob-and-tube wiring systems?
An AFCI circuit breaker will trip and clear the circuit when a
line-to-neutral arc occurs (often caused by the melting of the
conductor insulation at loose terminals) within three to eight
half-cycles, whereas a standard circuit breaker might not open for many
hundreds of half-cycles. Note: If the AFCI is dual listed as a GFCI,
the two wire receptacle can be replaced with three-wire receptacles and
no equipment grounding conductor is required to be run to the
Ask insurance DIRECTLY! Some people cover up the remaining knob and
tube so they qualify for homeowners insurance. Like replace everything
just one minor trouble, if you have a fire in the future the presence
of knob and tube will be discovered and inssurance can refuse to cover
you. You could lose everything....
The other issue is resale value, rules continue to get tighter. So
attempoting to get around the replace K&T today may not work in the
future espically when you decide to sell and decrease your homes future
I think you should replace all the K&T and get on with life. Nothing
lasts forever, how many vehicles have you purchased in a lifetime? how
many $$$ have you spent.
Now balance this spending against a INVESTMENT in your home! Homes are
investments because they go up in value!
Vehicles go DOWN in value so they arent investments.... more like a
It (AFCI) will provide some protection but nothing's perfect.
K&T is usually not too hard to replace since it is usually installed in
accessible areas and the old wire can be used to pull new cable where it is
not. Remember the new wire doesn't need to follow the old route at all and
some of those fixtures can be tied to other existing branches. Hardest part
is retrofitting the j boxes if there were none.
On 10 Aug 2006 14:52:48 -0700, firstname.lastname@example.org wrote:
Talk to your insurance and local code enforcement people.
But.... the GFCI protection protects people from shock, but will not
stop a problem commonly associated with K&T. Fire.
tom @ www.Consolidated-Loans.info
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