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Knob and Tube wiring

What is Knob and Tube Wiring?

knob and tub wiring - ceramic knobsKnob and Tube wiring - ceramic tubesKnob and Tube wiring can still be found in many older Century homes right up to those built just before the Second World war.  

Even today, across North America there are some installations (mainly industrial) that use Knob and  Tube wiring.

The name Knob and Tube comes not from the wiring itself, but from the Ceramic Insulators that are used to support the wires around bends and through the beams of the house.

The Knobs are shown in the picture on the left. These were designed to support the wires and help them around bends.  The Tubes are shown in the picture on the right.   Holes  were drilled through the woodwork of the house and ceramic tubes installed to insulate the wood from the wiring.

Is it unsafe?

The ESA (Electrical Safety Authority) in Ontario, have stated publicly the Knob and Tube conductors in good condition and that have not been inappropriately altered will not present undue hazards.

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

That said, it is worth noting that modern electrical installations contain safety benefits not found in older electrical systems, especially Knob and Tube, these include:

  • Dedicated electrical circuits for certain types of electrical equipment or appliances.
  • Grounded and bonded receptacles, switches and light fixtures.
  • Tamper resistant receptacles in homes.
  • Ground fault circuit interrupters in bathrooms, near sinks and outdoor locations.
  • Arc Fault Circuit Interrupters in bedroom receptacle circuits.

In addition, Knob and Tube wiring will not support the generally larger electrical capacity most modern households need.

Why not leave it alone?

So why the worry if these systems are not considered dangerous (under the right circumstances) or illegal?

The problem is with insurance.  Insurance companies have built a universal practice for Knob and Tube.  Even where there is a n ESA Certificate of Acceptance for Knob & Tube wiring, the Insurance companies stick to their policies. They choose not to insure.   Where an Insurance company will insure a home with Knob and Tube wiring, the premiums are so high, they say to cover the risk factor.   Sometimes the money spent in 3-4 years of paying the higher premiums would equate to the price of re-wiring.   Keeping Knob & Tube and paying higher premiums does not give you the other benefits that comes with rewiring.

Replacing Knob and Tube

The average cost to rewire a single storey home, including repairs to the walls ceilings runs at around $6000-$8000.  A two storey home cost more at around $7,500-$10,000.  These estimates are based upon industry standard figures.  They assume that no major issues are found during the exercise. 

The bulk of the work (removing/replacing drywall & ceilings, ripping out the old Knob and Tube, installing new Receptacles and running the NM wiring) does not have to be carried out by a Licensed Electrician, but you need to have a Licensed Electrician:

  • Turn the power off and disconnect BEFORE you start work,
  • Inspect and perform the final connections of the Branch Circuit to the service Panel after you’ve completed the electrical work and before you cover up any of the cable with drywall, and
  • the work needs to be inspected by a Licensed Electrical Inspector.

Doing most of the work yourself as indicated above, if you know what you are doing and adhere to the Electrical code of the location the property is in, can save you, on average 20-50% of the costs, but it is going to take you time and require several inspections.

Remember, replacing Knob and Tube is not a huge expense when you compare it against the price of the home.  

To explain let me take a couple of examples, and Home costing $225,000 that has Knob & Tube, and a used car costing $12,000 that needs new tires.  

Say for example replacement of the Knob and Tube costs $8,000, and a car tire costs $140. 

  • Replacing the car tires would cost 5% of the cost of the car. 
  • Replacing the Knob & Tube in this example would cost 4% of the price of the property.

Having to replace tires is unlikely to deter you from buying a car you loved.   If you have the budget, why should it stop you buying the house you love?


There is no reason why Knob & Tube wiring should deter you from buying your dream home.

If you’ve fallen in love with a property, love it’s location and it is well within your budget, then Knob & Tube wiring shouldn’t deter you from buying it. 

You need to be aware of the Insurance issues. If you can’t get finance without insurance, and you can’t get insurance, that is really the end of it.

The deal however is not dead and you may still be able to get your dream house if:

  • You have the funds to purchase the property and complete the work either with or without insurance.
  • You can arrange for finance on the basis that the work will be completed, (in this case you may be able to use quotes to have the purchase price of the house lowered).
  • You can get the existing owner to do the work prior to closing (get the paperwork to show it’s done properly).