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Knob and tube electrical wiring can become an electrical and fire safety issue

Knob and tube electrical wiring was installed in houses until the late 1940s. It often makes insurance companies nervous, because exposed horizontal runs of wiring have been or can be used to hang things, such as metal coat hangers, which can result in an electrical shock if the insulation has broken down.

The critical danger with knob and tube wiring is hardening of the rubber insulation. It can become brittle and will then fracture easily, when the bare wire can be seen.

Replacement of the exposed, horizontal runs of the wiring is normally an acceptable upgrade for the insurance companies, although you will be wise to confirm this with your specific insurer.

Existing knob and tube conductors concealed in walls, floor spaces, etc, supplying general lighting and receptacle circuits are permitted by the Ontario electrical Safety Authority to remain in place if:

• they are protected by a 15 ampere fuse or circuit breaker (This is a maximum); and
• no additional outlets have been added to the original installation so as to overload the circuit; and
• the wires (especially the insulation), where visible, appear to be in good condition.

The Ontario Electrical Safety Authority has issued a Technical Bulletin on the subject of knob and tube wiring; we recommend you read this. (http://www.esainspection.net/pdf/Flash_Notices/06-04-FL.pdf)

We recommend that you choose a reputable and qualified electrical contractor, although you can do the work yourself if you follow sensible safety precautions; (see below).

If you choose to do any replacement work yourself, it will most likely be in an unfinished basement, with reasonably good access to the wires. Remember that only original splices in knob and tube wiring are acceptable. Any new joints must be made in a junction box.

Knob and tube wiring does not have a ground wire, and this might be the time to consider providing a ground for specific receptacles, those where the ground wire can easily be pulled to the receptacle. In most rooms, not having a ground is not a great disadvantage. Think about how many appliances, such as radios, lamps, vacuum cleaners and most other small appliances, do not require a ground. If however it is necessary to use a three pin plug, replace the receptacle with a GFI receptacle. Do not remove the ground pin from the plug

If you have to re-wire, consider taking the opportunity to increase the number of receptacles, which originally were likely minimal. Your new wiring should, of course, be a three wire grounded system.

1. Never work on a powered electrical system; always remove the fuse or switch off at least the breaker feeding the switch or receptacle you intend to correct. It is safer to switch off the main disconnect or main breakers and de-power the whole house. Remember to let everyone know what you are doing, and put a sticky note by the breaker or fuse you switched off.
2. Never open the mains feed side of any electrical panel, as there is no disconnect to de-power this and you are entirely unprotected.
3. If you are working on the panel, you must de-power it using the main disconnect or main breakers.
4. Before you start working, check that the power is off at the receptacle or switch using an electrical tester.
5. Keep notes about which receptacle or switches you corrected; remember it is better to correct them all rather than just a few problematic ones.
6. Take photographs to document the correction that you did; a future buyer might wish to see these.
7. After the work is completed you can arrange for an inspection by the Electrical Safety Authority, who can issue a Certificate of Inspection for your records and possibly for your insurance company.