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Knob and Tube Wiring


What is it?


Knob and tube wiring is the original wiring method used from the late 1800s until approximately 1945. It is a system that involved stringing individual conductor insulated wire across porcelain insulators called “knobs,” and through other porcelain insulators called “tubes.”


Is Knob and Tube wiring safe?


This is an often-asked question. There are a number of concerns with knob and tube wiring. Some of them are listed here...

It is an ungrounded system, which provides a greater chance of shock or electrocution and damage to sensitive equipment.

It is very old wiring (at least 62 years old, at best), and in many cases has deteriorated, cracked or is missing insulation, which can lead to fires.


The original switches and receptacles are not CSA approved, and in many cases the contacts are loose inside the device, which makes for a poor electrical connection and potential for fire.


It is common to find that newer wiring has been improperly connected to knob and tube wiring by amateurs, resulting in dangerous conditions in the form of shock hazard, reverse polarity problems, switched neutrals, overloaded circuits, and fire hazards, just to name a few.


Like other components of your home, such as your roof, furnace, air conditioning and plumbing, there comes a time when replacement is necessary. That time has come for knob and tube wiring.


So, to answer the question “is knob and tube wiring safe?” we have to say that in our opinion, the answer is “NO.”

What can you do about it?


In our opinion, rewiring the home is the only solution that correctly addresses knob and tube wiring. Other solutions like eliminating it only where it is open to view (in basements and attics), or installing GFCI receptacles, are band-aid solutions that we do not recommend. Although installing GFCI protection may be acceptable to the Electrical Safety Authority, GFCI receptacles may not work in situations with shared neutrals (commonly found in knob and tube wired homes).


Rewiring the home is an investment that adds substantial value to your home. It is a major project that may take 1-3 weeks, depending on the size and construction of the home. It is the best solution to serve your long-term interests.


Big Island Electric, Inc. is an electrical contractor and electrical services company in Hawaii.  73-4157 Huliko’a Drive Unit #C, Kailua-Kona, Hawaii 96740


Phone: 808-329-2660 | Fax: 808-329-2250 | Email:

License # C25414

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