Historic Building Inspectors
Association
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Frequently Asked
Questions
from Historic Home Buyers/Owners
This months question:
Knob & Tube Wiring
I am in the process of purchasing a Victorian home built around 1880. There is
a 100 amp fuse box and old cloth covered wiring that passes through porcelain
tubes. An older couple currently lives in the home which has had very little
updating. Will this wiring and the old fuse box need to be completely replaced?
Will we need to tear open the plaster walls? Any help would be appreciated.
Thanks, JG
Amongst experienced inspectors and even
electricians, there are varying opinions on how knob and tube wiring should be
addressed. The two most immediate concerns are:
1) If it is encapsulated by insuation that was added to an attic, wall
cavities, crawlspace, etc.
2) Improper alterations can seriously effect the original design.
The comments below are general and do not apply to all situations. This should
not be considered advice and certainly can not replace the need for a complete
pre-purchase inspection by a qualified professional inspector or licensed
electrician. |
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Answers
From your description, it sounds like you
have knob and tube wiring in your home. This wiring is ungrounded, and, by
today's standards, is not safe. Problem is that, overtime, the insulation wears
thin or falls apart, or is eaten by mice, and the conductor is exposed. This
can, under certain conditions, cause arcing and lead to a fire, or cause
someone to be shocked, should they come in contact with a bare wire. Sometimes
folks have tapped into the existing wiring, to add other circuits, and these
connections are also unsafe. To answer your questions - it is strongly
suggested that all old knob and tube be removed and replaced with modern
wiring. As for breaking through the plaster, an electrician experienced with
older homes can oftentimes fish new wiring through the often uninsulated walls
without too much destruction.
Good luck. Ken Salvo, HBIA Member Inspector
Personally I have renovated at least 10
homes with this set up. The 100 amp fuse box is minimal at best and I have
always replaced it with a breaker system. I have kept the cloth wiring in the
walls, except in kitchens and baths, where I have gone to new wiring with
GFI's. I personally have not seen the necessity of replacing all the old wire
behind the walls. Usually if it shorts a breaker will trip. Everybody is
different, for me unless the wire is totally damaged, I am going to use it.
Bob Congdon, HBIA Member Inspector
Local codes generally set minimum standards
for updating an electric system. When work requiring a permit is being planned,
this minimum updating usually is incorporated into the project. While it may
not be necessary to remove the fuse box for safety reasons, usually it cannot
accomodate modern usage levels particularly when it comes to 220 volt circuits
and expansion. Assume that the panel needs replacing. The exposed knob and tube
wiring in a basement usually does not comply with modern standards because of
open wire splices and other discontinued practices. Usually, it needs to be
replaced. Both of these work items will make your system safer and easier to
work with.
Replacement of knob and tube wiring in an attic or in walls is generally not
required but sometimes because of the placement of the outlets, desire for
grounded circuits, and configuration of the circuits, it is better to use new
wire.
I advise that you obtain a bid from an electrician for updating the system to
meet modern standards. Then, if possible, plan for and include a wish list of
additional outlets, lights and switches and new 220 volt circuits and obtain a
bid for this work as well. At the time of purchase, safety deficiencies to the
system and, to some extent, improvements such as a 220 volt circuit for a
clothes dryer can be topics for negotiation.
Most of the time when electric work is done in an older house some small access
holes will need to be cut in the plaster walls and ceilings. Discuss this with
the electrician and plan for it.
In our area, some property insurance carriers want to know if a house has a
fuse box. This probably means that they may be charging more for the policy or
not underwriting houses with the older systems.
Good luck. Jon White, HBIA Member Inspector
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