by Ted Olechna
Knob and tube wiring, more recently referred to as open
wiring, was a wiring method used in the early 1900s to
1940s in the residential dwelling sector. Over the years
wiring installation practices have changed in the residential
sector and knob and tube wiring is no longer installed;
however, parts continue to be available for maintenance
Typical knob and tube installation
Existing knob and tube conductors concealed in walls, floor spaces, etc; supplying general lighting and receptacle circuits are permitted to remain in place if:
· They are protected by a 15 ampere fuse or circuit breaker; and
· No additional outlets have been added to the original installation so as to overload the circuit; and
· The conductors, where visible, appear to be in good condition.
If your apartment building has knob and tube wiring, we recommend that you follow these guidelines:
· Arrange for a qualified electrical contractor check the “knob and tube” conductors in your existing installations for sign of deterioration and damage; or request a general inspection from ESA. The General Inspection report will identify visible electrical safety concerns in your electrical wiring.
· “Knob & tube” conductors should be replaced where exposed conductors show evidence of mechanical abuse and or deterioration, poor connections, overheating, alterations that result in overloading, or if changes to wiring contravene any section of the Ontario Electrical Safety Code.
Knob and tube wiring may not have the electrical capacity to meet today’s needs. As a result, modifications may have been made to the electrical system with what the Electrical Safety Authority classifies as unsafe practices:
· Improper use of extension cords – using improperly rates extension cords, or using extension cords as permanent wiring;
· Improper fuse replacement – using 20 or 30 amp fuses to replace15 amp;
· Improper connections - adding receptacles and outlets on existing circuits or improperly connecting to the knob and tube wiring (this work should be done by a qualified electrician);
· Removing ground pins – ground pins on power bars or electrical equipment should not be removed to accommodate the two pin receptacles used in knob and tube wiring (2 pin to 3 pin are not permitted)
· Improper replacement of two pin receptacles. If you require a three prong receptacle, only use a GFCI receptacle
Where grounding type receptacles (three
pin) are used in existing knob and tube installations
to replace the ungrounded type (two pin) receptacle special
caution must be exercised. Rule 26-700 (8) permits a Ground
Fault Circuit Interrupter (GFCI) type of receptacle to
be installed on an ungrounded circuit without a bonding
conductor, this is the preferred method. Rule 26-700(7)
provides a second option which permits the installation
of an external bond conductor to the system ground conductor
or metallic cold water pipe if they are bonded to ground.
This method is not as desirable and may be difficult to
Two Pin (ungrounded)
Three Pin (Grounded)
Ground Fault Circuit Interrupter (GFCI) type of receptacle
While knob and tube conductors in good condition and has not been inappropriately altered will not present undue hazards it is worth noting that modern electrical installations contain safety benefits not found in older electrical systems.
· Generally larger electrical capacity and more electrical circuits reducing the need to use extension cords
· Splices and joints made in approved electrical boxes
· Dedicated electrical circuits for certain types of electrical equipment or appliances
· Grounded and bonded receptacles, switches and light fixtures
· Ground fault circuit interrupters in bathrooms and outdoor locations
And with the latest edition of the Ontario Electrical Safety Code
· Arc Fault Circuit Interrupters in bedroom receptacle circuits
· And GFCIs near kitchen sinks.
Anyone planning to modify 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.