Knob and tube wiring gets its name from the ceramic "knobs" used to keep the wires isolated from objects and
the wood joists the wires run along, and the ceramic "tubes" that were used to isolate the wires from the wood joists
that they ran through. Knob and tube wiring was installed from the early 1900's until the late 1940's and in some instances
into the 1950's.
In a "typical" residential house circuit (general usage receptacles
and lighting), the difference between knob and tube wiring and the "modern" wiring used since the early 1960's,
is that knob and tube wiring consisted of a black (hot) and white (neutral) wire. Both wires ran separately to receptacles,
switches and fixtures whereas the wiring used today consists of a black (hot) and white (neutral) wire plus a ground wire,
all contained inside an outer sheathing. Since 1979, and some incarnations before, the sheathing has been made of plastic.
Today's wiring is mostly gauge 14 wire that is to be protected by a 15 amp fuse or breaker, whereas knob and
tube wiring could be a mixture of gauge 14 wire or gauge 12 wire (capable of handling 20 amps) but is to be
protected by a 15 amp fuse or breaker, and while being separated and run as single wires actually run cooler than today's
In some of the homes
built in the early 1900's there are no outlet boxes at fixture locations. Outlet boxes can be added with minimal damage
Due to the usage of high wattage light bulbs in fixtures that were designed only
to handle 25-40 watt light bulbs, the heat from the light bulbs could make the insulation on the knob and tube wiring become
brittle and in some cases fail, leaving bare wires at the fixture. This could result in a fixture becoming "live"
or the two wires touching each other causing sparks and therefore a blown circuit, or much worse a fire. When this occurs
it is usually at an totally enclosed fixture that has a very low profile. This conditions is seldom evident at a ceiling
location where the fixtures hung down from the ceiling. This condition is seldom at wall sconce locations
either. Whereas wiring manufactured since 1986 is rated at 90 degrees Celsius, knob and tube wiring never had a heat
rating. Wiring through the late 1950's to the late 1970's had heat ratings of 60 degrees Celsius and wiring from the
late 1970's up to 1986 had heat ratings of 75 degrees Celsius. It is possible to put new insulation on the knob
and tube wires and then cover them with a thermoplastic covering rated at 90 to 110 degrees Celsius. At some attic
locations we are able to remove the wiring back to where there is no damage, install a proper junction box and refeed the
fixture with new wiring.
Knob and tube wiring is ungrounded and is connected to recptacles
that have only two slots or openings. Today you can only purchase receptacles that have a third hole. that
being for the ground pin on a grounded appliance or tool. It is illegal to connect a grounding type receptacle onto
ungrounded wiring (even if the ungrounded wiring is not knob and tube). Rule #26-700(8) in the Ontario Electrical Code
allows the installation of a grounding type receptacle that has an integral Ground Fault Circuit Interrupter (GFCI) onto ungrounded
wiring. This type of receptacle will shut down if it detects a leakage of current to the wire connected to the ground
**Never cut off a ground pin from the cord of any appliance or tool. Not only
is it unsafe and can cause a serious shock hazard but the appliance or tool has been altered and is no longer CSA approved.**
Whereas most knob and tube wiring that runs through covered walls, ceilings and floors, and in those
that have not been tampered with, the wiring is more likely to be as good as the day it was installed. The area's that
the wiring was accessible to the "do it yourselfer or amateur" is in attics and basements. Because of this,
we see lots of cases of incorrect and often dangerous alterations or additions. Qualified electricians can make the
necessary repairs, corrections or replacements (if deemed necessary) to bring the wiring back to a safe condition.
The one thing we can't know is if there is any dubious wiring or connections inside of walls that have been altered.
Houses that have knob and tube wiring also have those wires protected by fuses (unless the service
panel has already been replaced with a breaker panel), thus being vulnerable to over fusing, which makes the wires run "hot"
and make connections along the system susceptible to breakdown, or worse a fire. The elimination of the fuses and installation
of breakers can help solve the problem.
What do you do?
More and more insurance companies are refusing to insure homes with knob and tube wiring. The first calls we received
in regards to this was as far back as 1993.
You can contact the Electrical Safety Authority and set up through
them an Elec Check inspection, the cost is 399.00 + tax. If your house passes inspection you will receive a certificate.
If not, they will produce a list of defects that you should have corrected, or additions that they deem necessary. Once
these corrections have been made by a licenced electrician an ESA inspector will come back and re-inspect. Upon approval
you will receive a certificate based on the work that was done. The costs associated with these types of repairs are
determined by the size of your house and naturally the condition the wiring is in and how much updating has been previously
done. Typically the costs run between $400.00 - $3000.00, plus re-inspection fee and HST.
not all insurance companies are interested in an inspection, but rather insist on complete replacement of the knob and tube
wiring. Rewiring a house with today's standard (NMD) wiring is much a problem of access. If your house has an
unfinished basement we can rewire most of the main floor receptacles and feeds to the switches from below. In a bungalow
style house we can access the lighting fixtures and switches from above in the attic. If your house has two or more
stories the problem is that there is no access to the first floor light fixtures and switches without opening the walls and
ceilings. This is the same problem for any room with a finished floor or a flat roof above. The costs associated
with these types of repairs are determined by the size of your house and naturally how much updating has been previously done.
Typically the costs run in between $4500.00 - $20,000.00, plus re-inspection fee and HST.
For over sixty years Piper Electric has been installing and upgrading consumer's electrical systems
in the Greater Toronto area. For those that cannot afford to remove completely the knob and tube wiring We feel that with
the additions of new wiring and extra outlets on new circuits to specific heavy duty appliances, the load on the existing
knob and tube wiring will be greatly diminished. Most electrical items that you have throughout your home (table lamps,
radios, clocks, stereos, cordless phones) are supplied by two prong cords and are not heavy usage items.
Recently we have been receiving more calls from previous and potential customers who have already had the Electrical
Safety Authority out to their homes for their initial inspection. They had already been directed to the Electrical
Safety Authority by their own insurance company.
It is up to you and your insurance company
as to how you will handle this dilemma that is in your home.
Which ever way you decide to address the wiring in your home, let the expertise of Piper Electric look after your project.
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