Is Knob & Tube Electrical Wiring Safe?

July 15, 2015

Knob and tube electrical wiring, also called open wiring, was a common wiring method used in the 1900’s to the late 1940’s. It is estimated that there were approximately 200,000 homes, with knob and tube wiring, built in BC during this time, with a large number located in Abbotsford, Langley, and the Lower Mainland. Contact one of our residential electricians to find out how we can help you update old knob and tube wiring.

knob and tube electrical wiringKnob and tube wiring is a single conductor, ungrounded system, where electricity is brought from a 60 amp service to different areas of the home by running copper wires, covered with a cloth and rubber insulation sheathing, through the walls, attic and floor spaces. As seen in the photo, porcelain knobs are used to secure the wires in place and keep them from contacting combustible surfaces. Where ever the wire needs to cross through a stud or joist, holes are drilled and fitted with porcelain tubes through which the wire has been threaded, thus the name, knob and tube wiring. The alternate name of open wiring suggests the importance that an open airspace be maintained around the wire at all times to prevent overheating.


electrical knob and tube wiringIf the knob and tube wiring system remains unaltered, has been carefully maintained, and all repairs have been made by a knowledgeable electrician, knob and tube wiring would still be safe to use today. Unfortunately this is almost never the case. As the system ages and deteriorates, porcelain knobs and tubes may crack or break, old wires sag and fray, and the sheathing turns brittle and falls off, exposing the live wires. Homeowners improvise their own repairs as replacement parts may not be readily available which results in some very dangerous modifications.

unsafe knob and tube electrical wiringHomeowners unknowingly create a dangerous situation when household insulation is installed over the tube wiring. The cloth/rubber sheathing around the wires is not approved for contact with insulation as it requires an unrestricted airspace around it to dissipate any build up of heat. Add to this picture the unsafe practice of modifications made to modern appliance cords in order to make them compatible with the old and outdated 2 prong receptacles, extensive use of extension cords and power bars in order to glean more power than the aging electrical system was intended to provide, and you have the potential for a serious problem.

A combination of knob and tube electrical wiring and modern electrical wiring is what is usually found in these older homes today. If this work has been done by someone unfamiliar with the unique requirements of knob and tube wiring, the potential for disaster is certainly present. The tinder dry beams in this attic would have been instant fuel for a spark from this dangerous wiring combination of old and new. But in many cases the “updating” is not visible in the attic or basement. Rather, it is hidden behind the walls as it was probably done during a previous renovation or addition to the house.

Aside from deterioration as a result of age, the majority of problems with knob and tube wiring are caused by tampering and when alterations are made to the original system by amateur handymen. So, to answer the question is knob and tube electrical wiring safe, the answer is NO. This method has long out lived it’s time and should be replaced with current products and modern procedures.


Insurance companies are wary of homes with knob and tube wiring and view this wiring method to be a definite safety hazard, and therefore a claim waiting to happen. Some of our clients have reported paying extremely high insurance rates as a result of the knob and tube wiring. At the very least, an inspection by a certified electrical contractor is requested which, given the information shared above, usually requires that the knob and tube be completely replaced before a homeowner’s policy is issued or renewed. This leaves the homeowner with little choice but to address the problem.


Realistically, complete replacement of the old wiring is the best option. The presence of knob and tube electrical wiring means the house was probably built 60 to 100+ years ago when this was the only wiring method available. Demands on the home’s electrical system were minimal back then, as lighting was often spartan at best, and homeowners owned only a few small electrical appliances. Fast forward to today and compare this to your daily electrical needs and you soon realize just how out dated the knob and tube system is.

Removing the old knob and tube electrical wiring and replacing the entire system with new copper wiring to meet today’s electrical safety code standards is without question the best solution. Replacing the old ungrounded switches and receptacles with CSA approved devices is another important safety measure. If it has not already been done, installing a new electrical service panel at this time, that provides for the needs of today’s average household usage and also allows for any possible future needs or plans, addresses the problem of blown fuses, over loaded circuits and other safety concerns.


old home knob and tube electrical wiringSo you’ve found a beautiful heritage home for sale in the real estate market that is just perfect for you. You love the home’s history, character and location. There’s only one problem. A home inspection has revealed the presence of knob and tube wiring which is still being used to bring electricity to part of the home. You know that some modifications have been made to the original system but there is no documentation to verify who did the work. What are your options?

A site visit by one of our licensed electricians will provide you with exactly the information you need. As each home is unique, it is important for us to do a careful assessment as to the exact plan of action that is best suited for your specific situation. In most cases, this job may take a week or more depending on the size of the home and complexity of the task, with costs ranging from $5,000 to $25,000+. Keep in mind that the resale value of your home will increase after this work is completed, so not only is your home safer for you and your family, your home is also now more desirable to potential future buyers.


In most cases knob and tube wiring work can be done without the need to relocate the homeowner, although the fewer obstacles (furniture) in the technician’s way, the more efficiently the work progresses. Homeowners need to be aware that it may be necessary to create some openings through which to access or pull circuits. Our approach is always to cause as little damage as possible. As a result, the amount of follow up repairs is kept to an absolute minimum.

The beauty and charm of your heritage home remains intact but the safety concerns regarding the electrical system have been eliminated.

Call Blue Crest Electric Ltd. today for fast and friendly knob and tube wiring service or professional electrical service. With the right team working for you, the job will be done right and in no time.

Client Testimonial

“I recently had my old knob and tube electrical system updated to modern wiring by Blue Crest. It was great knowing how much it was going to cost me in advance instead of wondering how much more it would be every time they discovered some strange new wiring configuration. The electricians were always professional and friendly and did their best to make everything exactly how I wanted it. Even though they re-did the wiring in almost all of my house (some had already been upgraded), they only cut about 6 small holes in the ceiling–everything else was done by “fishing” through the walls of existing openings. They cleaned up after every day of work and had as much electricity on again in the evenings as I needed. The office staff was great. Overall, I found the experience entirely positive.” – C. Marlor, Mission

“My home had knob & tube wiring and Blue Crest rewired my home. I was presented with a price and a plan which Blue Crest delivered on without exception. These people were polite, careful and punctual. Blue Crest went above and beyond in their service, finding solutions to issues that could not be foreseen. I won’t hesitate to use Blue Crest again or to recommend them to others.” – Jack D. – Abbotsford

Thanks for your review Jack. Homes with Knob & Tube wiring will also have delicate lath & plaster wall construction. Rewiring these heritage homes requires an electrician with specialized skills and exceptional creativity to keep the amount of wall damage to a minimum. Our team is especially proud of this particular home rewiring project, because it was completed without a single hole made in the walls. This saved the home owner considerable costs in wall repairs and resulted in a faster renovation completion date, not to mention less mess and inconvenience.

View more testimonials

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