Knob & Tube Wiring - Myths, Facts & Home Insurance

Most home purchasers will experience difficulty getting their home insured when Knob & Tube wiring is found to be present. The purpose of this article is to remove some of the myths surrounding this topic & share some facts.

Knob & Tube wiring or Open wiring as it is sometimes referred to, was the electrical system that was used in the first half of the 1900’s. It consist of two wires, live & neutral (no earth). Insulator knobs were used to keep the wires isolated & ceramic tubes used to line holes through wooden joists/studs. Insurance companies deem this older style of wiring to be unsafe & to be a fire hazard, however according to the Electrical Safety Authority, knob & tube wiring can be safe & functional.

It is recommended that a qualified electrician  inspect the wiring to determine its safety. With proper documentation from a certified electrician many insurance companies will insure a home with Knob & Tube. 

• You should be aware that there is no ground wire in a Knob & Tube wiring circuit, which may be an issue for today’s lifestyle, high electricity usage and technology. 
• Knob & Tube Wiring is only rated for 15 Amps, it should be protected by a 15 Amp fuse or circuit breaker. Devices rated for more than 15 Amps cannot be used with Knob & Tube wiring. 
• If three pin devices are to be used on a Knob & tube outlet, then it is recommended that a GFI be installed.
• Also, there are potential fire hazards with the break down of the insulation around the knob and tube wiring that comes with age, and should the black and white wires make contact.

Some home insurance companies will refuse to insure homes with knob and tube wiring. However, there are companies that continue to offer regular priced policies for homes with knob and tube wiring and others who ask a premium for this insurance. If you have any concerns about the safety of your knob and tube wiring, you can hire an electrician to update your home wiring. The average cost per room is approximately $800 to $1000 per room, expect to pay more for a two story home than a bungalow. Also ask if the quote covers all repairs to the walls, floors & ceilings. Keep the receipt to show prospective buyers when it comes time to sell.


If you purchase a home in the Toronto area where knob and tube wiring is still part of the electrical circuit, ask your realtor & your insurance company for advice on securing insurance before the deal firms up. Insurance companies will often ask you to estimate the percentage of knob & tube wiring that exists in the property before making a decision on insuring the property. This will help to mitigate any insurance problems when the closing date approaches.

Homeowners who are planning to modify their knob and tube wiring, or any other electrical wiring, should have the work performed by a licensed electrical contractor or electrician and arrange for an electrical inspection by Electrical Safety Authority.

Myths

• Knob & Tube wiring is unsafe.

• All knob and tube wiring must be disconnected and replaced.

• The Ontario Electrical Safety Code no longer recognizes knob and tube wiring as an acceptable wiring method.

Facts

• Knob & Tube wiring is safe, provided it is properly maintained by competent licensed people as outlined above.

• The Electrical Safety Authority as well as the Ontario Electrical Safety Code recognize and accept knob and tube wiring methods.

• The Ontario Electrical Safety Code 2002 edition contains rules that govern the installation of open type wiring methods (knob & tube). Rules 12-200 to 12-224 set out the minimum safety standards for the installation of open wiring, which may still be installed to this day.

Aluminum Wiring

Aluminum wiring in residential installations
Issues with aluminum wiring
Since January of 2003 the Electrical Safety Authority has received an increasing number of questions about the safety of aluminum wiring. In particular, purchasers or owners of homes built from the mid 1960’s until the late 1970’s with aluminum wiring are finding that many insurers will not provide or renew insurance coverage on such properties unless the wiring is inspected and repaired or replaced as necessary and this work is inspected by ESA and a copy of the certificate of inspection is provided to the insurer. In some cases the insurer may require replacement of the aluminum wiring with copper wiring. Check with your insurance company for their requirements.

Some homes may have a mixture of aluminum and copper wiring.

Reported problems with aluminum wiring have been related to the overheating and failure of aluminum wiring terminations. This is due to aluminums tendency to oxidize and its incompatibility with devices designed for use with copper wiring. Warm cover plates or discolouration of switches or receptacles, flickering lights, or the smell of hot plastic insulation may evidence these problems.

Each home will be different and must be assessed on its own. It is highly recommended the homeowner hire a licensed electrical contractor who is knowledgeable in the special techniques required for working with and repairing aluminum wiring. The contractor should do an assessment, make the necessary repairs, and have the work inspected by ESA. The homeowner should obtain a copy of the Certificate of Inspection for their records and for their insurance company (if requested).

As mentioned above, where problems exist with aluminum wiring they are usually found at termination points. This necessitates the opening of all outlets (receptacles, switches, fixtures, appliance connections, and in the panelboard) and visually inspecting terminations for signs of failure and overheating without removing or disturbing the devices or wiring. There should be no signs of overheating such as darkened or discoloured connections, melted insulation, etc.

Where problems are found the damaged aluminum conductor should be cut back to remove the damaged portion and then the necessary repairs made.

Required markings for devices used with aluminum wiring
Replacement receptacles and switches shall be installed in compliance with the Ontario Electrical Safety
Code and marked as follows:

All terminations of aluminum conductors shall be to devices marked as per Table F1 and Photo F1; this includes the bare bond conductor as well. Rule 12-118(3) provides two exceptions to this requirement. The first exception is for devices or fixtures with wire leads, in which case the joint between the wire lead and the aluminum conductor shall be made with a wire connector approved for copper to aluminum connections and marked as per Table F1. The second exception is the outlet box bonding screw, which does not require approval for connection of the aluminum bonding conductor.

Photo F1 – Required marking for devices used with aluminum wiring

Terminations of aluminum conductors
Rule 12-118(6) of the Code requires the connection of aluminum conductors to wiring devices having wire binding terminal screws, about which the conductors can be looped under the head of the screw, shall be made by forming the conductor in a clockwise direction around the screw into three-fourths of a complete loop and only one conductor shall be connected to any one screw.

Devices with “push-in” terminations shall not be used with aluminum conductors.

An alternative to using copper/aluminum approved devices is to connect a copper wire “pigtail” between the aluminum conductor and the device connection screw of a device approved for copper only connections. Pigtailing also applies to the bond conductor, which is often overlooked. The wire connector used for the pigtail joint shall be marked as per Table F1.


Rule 12-118(1) states that adequate precaution shall be given to the termination and splicing of aluminum conductors, including the removal of insulation, the cleaning of the bared conductor,  the compatibility and installation of fittings.

Aluminum conductors are softer than copper and care must be taken that they are not nicked or cut, or crushed during termination. Nicks, cuts, or crush spots at terminations result in a weak spot that may result in breakage of the conductor or a hot spot.

Rule 12-118(2) requires that a joint compound be used with stranded aluminum conductor connections, but does not require it for solid aluminum conductors. Even though not required by the Code, it is recommended that bare ends of solid aluminum conductors be coated with approved joint compound. Note: The compound is conductive and should be used sparingly and any excess compound should be removed.

Where pig tailing is used, Rule 12-3036 must be considered with respect to the minimum volume of box required to contain the existing as well as the new conductors and connections. Where there is not enough room in the existing outlet box, a surface mounted extension box may be required to contain the extra volume necessary to safely accommodate everything.

General inspection
Question
If ESA completes a general inspection, does the OESC require an older house that is wired with
aluminum wiring to have all non-CU/AL devices replaced with devices approved for connection to aluminum wiring (or have copper tails installed as per information included in this Bulletin ( 12-28-*).
Answer
No, If the devices are the original ones installed and show no visible signs of overheating or other damage, then they are not required to be replaced (it is recommended only). If a device shows any visible signs of overheating or other damage, then replacement is required. If any of the devices have been replaced in the past with newer devices (ie: Decora style), then they are not original and are required to be replaced with a Code compliant installation.

Rationale
Rule 2-300 requires that operating electrical equipment be kept in safe and proper working condition and
that defective equipment shall either be put in good order or permanently disconnected. Where there is
no evidence of deterioration of the wire, the termination, or the device, then the Code does not require
that repairs be made.
Myths
• Aluminum wiring was recalled because it is known to be a fire hazard.
• Aluminum wiring is no longer used for interior wiring systems.
Fact
• The Ontario Electrical Safety Code permits the installation of aluminum wiring.
• Adequate precautions shall be given to the terminations and splicing of aluminum conductors;
• Aluminum wiring itself is safe if proper connections and terminations are made, without damaging
the wire and devices approved for use with aluminum wire are employed.
• Aluminum wiring is widely used today for larger commercial and industrial feeders. Electrical
distribution companies use it widely throughout their distribution systems including the supply
service cable to most residences; in fact it may still be used today for interior wiring systems in
residential homes as well as other structures. Aluminum wiring itself is safe and if proper connections and terminations are made without damaging the wire and using approved materials installed in accordance with the Ontario Electrical Safety Code and the
manufacturer’s instructions, there should be no problems with the aluminum wiring installation.