Knob and tube

Good day, Nick, Nachi …
I’ve just joined this fine group of people and have enjoyed taking several of the online exams.
During the electrical exam there was small chapter on Knob and Tube wiring. Working in Toronto Ontario as a construction site superviser/manager (soon to be home inspecter) doing residential renovations we come across it a lot. One thing this chapter did not discuss was the shared neutral. Perhaps it’s a difference of US vs Canadian standards. Your questions did seem to be geared towards US building code requirements. As an example, min height of a railing 5’ 11" above grade is 3’6" in Ontario. I do not believe it’s the same in the US.
Here in Ontario when Knob and Tube was enjoying its install heyday, there was only one neutral wire installed in the house. In today’s modern home, it is all too easy to overload the that lone heavily branched wire. This is the reason Knob and Tube is unsafe and should be replaced in Ontario. Now perhaps in the US Knob and Tube had a neutral for each circuit?
I think you are remiss in not including this information.

Hi to all,

Alan, as author of this course, I feel equiped to answer your questions.

All my classes are based on US codes in particular IRC 2003 and common sections of NEC, yest there are differences between US and Canadian codes. I am not familiar with CBC. If any Canadian member wants to help me edit any of the on line courses to reflect Canadian codes I would be happy to work with them to do so, and would produce a Canadian version of my classes.

As to the common neutral issue, in the US I have never seen that, in fact with wiring of that period fused neutrals is the bigger issue down here.

Certainly if the system is using a common neutral, it is unsafe and in need of upgrade, whether you live in the US, Canada, or Russia. The neutral is a current carrying component.



Thanks Gerry for the quick reply.
Any Canadian references from me will be from the Ontario Building Code.
I do not presume to know the OBC as well as I think I should. But I would enjoy helping wherever I can. I will subscribe to apropriate threads as I find them or perhaps you can add me to an email list? or some such.
If you would like to warm up to the OBC, it’s available (free) online at the Ontario Government website. Although it is buried very deep. I have it as a single file. 14+mb. Just tell me where to post.

Please provide the link for the material you mentioned.

Sorry I have never seen two hots run through the home in Canada and only one neutral .
Roy Cooke

This is not the site I downloaded my files from but it appears to be here as a word doc.

I’m sorry, “2 Hot and 1 neutral”?
I need to clarify my statement. 1 neutral is run from the panel and is branched to every outlet and switch.

I think I am missing some thing Are you saying that there is two hot wires and one neutral .
If this is the case and the two hot wires are 240 volts on opposite phases then the neutral will only be carring the unbalanced part of the load .
Example line one 8 amps line two 3 amps then the neutral will only be carring the unbalanced part of the load in this case 5 amps.
I can not see why the neutral would be going to the switch.
Some how I think you might just have got part of the instruction incorrect.

Roy Cooke

From the service panel there is 1 neutral wire which services ALL lights and outlets throughout the house. This neutral wire was branched at the electrician’s whim, meaning the connections can now be found anywhere and everywhere. In walls, ceiling and attic spaces.
This system was usually installed with a 60 amp service. Most of these have now been upgraded to 100 amp panels, fused and or breakers. In Toronto, I do not know of any insurance company that would insure a home with Knob and Tube.
If you would like me to explain in more detail do not hesitate to ask.

Nice to have you on board!!Especially from Toronto!!!


Last I heard, The Co-operators will insure it with an electrician signing off on it of course.