Knob & Tube Wiring – Why should you care?


Knob & Tube Wiring – Why should you care?

There are several good reasons to care about whether you have knob & tube wiring:

  1. The size of the electrical service associated with knob & tube installations of the pre-1950’s are inadequate to support the demands of many modern appliances – posing a fire hazard
  2. Improper, or lack of, maintenance and improper tie-ins during renovations can cause safety hazards.
  3. Knob & tube wiring does not contain a ground wire.
  4. Many insurance companies will not provide home insurance if your home has active knob & tube wiring. They consider it unsafe or high risk. This can make home insurance difficult, but not impossible, to obtain (but it will generally require an electrical inspection for safety).
  5. Knob & tube can make it difficult to sell your home, particularly if the new owners plan to perform renovations. This is because the renovations will likely necessitate the replacement of the knob & tube wiring.

Knob and tube wiring has not been used in construction since the 1950’s. There has been debate about the safety of knob and tube wiring in older homes – and in Maine, we have a lot of these. On the surface of it, provided that knob & tube was installed properly by a qualified electrician, it doesn’t present a safety hazard.  If you’ve had an electrical inspection and know your system is safe, AND you continue to respect the limitations of the system -you could be fine for many additional years. Properly installed and maintained knob & tube wiring can be safe when you don’t overload the electrical system.

How do you know if the electrical system is overloaded? If your home has modern appliances like a microwave oven, computers, central air, newer kitchen appliances, etc. you should have your electrical system inspected to make sure its adequate. Knob and tube was generally installed on 30- or 60-amp services.  If you experience a lot of blown fuses, tripped breakers, or electrical shorts, you’re likely exceeding the capacity of your electrical system. Most homes today should be on a 100- to 200-amp service. Be safe – get inspected.

However, even if you aren’t experiencing the problems above,  most homes and buildings have experienced some type of renovation or expansion of the electrical system since the original installation of the knob and tube. Problems with knob and tube wiring are generally associated with maintenance of the system, and how upgrades and changes have been accomplished.

With knob and tube wiring, the hot and neutral wires were run separately, a couple of inches apart from each other.  As mentioned above, knob-and-tube wiring does not have a ground wire. The copper wires are held by ceramic knobs nailed into the wall studs or floor joists. Ceramic tubes ran through holes drilled in the studs and floor joists. The knobs and tubes protected the wood frame from the heat of the wires. Cloth or rubber was used to insulate the wires — and this is the primary issue with knob and tube wiring. If the electrical system has been abused in any way, the wire insulation will deteriorate leaving bare wires. Bare wires are a fire risk – especially in walls that also contain insulation.

If you have knob & tube wiring, get an electrical inspection to make sure the system is safe. And, for all the reasons above, you may want to consider upgrading the system to meet today’s needs and standards.

If you are interested in reading more on knob & tube wiring, here a few resources you may find helpful:

Knob and Tube Wiring – Yikes! by Amy S Rybacki, Home Renovation Consultant

Knob and Tube Wiring at Living With My Home


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Danielle administrator

3 Comments so far

ScottPosted on  12:53 am - Jun 15, 2012

I found this website to be very informative and interesting to read. Keep up the good work. What about panel inspections ? Do you do them ? I understand that the breakers should be exercised at least once a year.

    DaniellePosted on  2:30 am - Jun 15, 2012

    Thanks for the feedback Scott. Yes, we do perform panel inspections. Please call our office if you are interested in this service (207) 782-3734 or email Low-voltage circuit breakers should be inspected and maintained every 1 to 3 years, depending on their service and operating conditions. You’ve given me a great topic for the next blog post – stay tuned!

Should you replace your electrical panel? | Roy I Snow, Inc.Posted on  4:05 pm - Jun 21, 2012

[…] Roy I Snow, Inc. Electrical Contractors – family owned and operated since 1947 Skip to content HomeAboutDan SnowThe Founders – Roy and GertrudeBlogTestimonialsServicesContact Us ← Knob & Tube Wiring – Why should you care? […]

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