Knob and Tube Wiring is a Concern

Home Inspector with Smart Move Home Inspection LLC RT # 715

Knob and Tube Wiring is a Concern

The old knob n tube system was originally designed to carry very small currents. Back in the day, the most common need for electricity was for lighting. Today, the needs for the average family are considerably greater. More items will be plugged into the outlets drawing more electricity. Usually, the needed current is greater than what the knob-n-tube wiring was designed for. When you overload this old wiring, it becomes a very significant fire hazard and is one of the leading reasons that knob-n-tube wiring should be replaced in a lot of homes. However, not all homes need to be upgraded. If your home has this old system, you should hire a licensed electrician who has experience with knob-n-tube wiring to review it. Depending on the condition of the wiring, they may recommend removing all of the wiring, removing part of the system, or leaving it alone. One safety, non-expensive upgrade they may recommend is installing S-Type fuses to ensure that no one "accidentally" installs an oversized fuse in the main panel box or sub-panels. This helps prevent overloading of the wires.

Common Problems

In addition to the problems mentioned above, a professionally trained home inspector looks for insulation damage from rodents, people stepping on the wiring, and storage crushing the wiring. We also look for rolled or loose-blown insulation and debris from previous roof replacements covering the wiring. There needs to be a 3" space between the live wire and any flammables. Homes that have had insulation added in the attic over the wiring are just waiting for a fire to happen. As there are many do-it-yourselfers out there, we constantly see Romex wiring spliced into knob-n-tube to feed newly installed light fixtures, ceiling fans, or additional outlets. Remember, these lines were not designed for system additions and all of these greatly increase the risk of causing a fire.

                                                   ' Smart Move Home Inspection LLC'

Comments (5)

June Piper-Brandon
Houwzer Inc - Baltimore, MD
Piecing Dreams One Home at a Time
I see a lot of knob and tube wiring in houses I list for sale and always suggest that the new owner/investor would have to have the electric updated, it's my understanding that appraisers will notice things like that and insist that for a mortgage to be given that it be replaced.
Feb 28, 2008 03:56 AM

Hi June,

 There may be a possibilty in some areas where a house is inspected with a updated electrical box and some knob-n-tube wiring approved, however I really don't think the cost of replacement would be a good comparison to safety or the conveinance of having the updated branch circuits.   Thanks for the comment.


Feb 28, 2008 05:25 AM
David Salvato
David Home Inspection Service Home Inspector San Bernardino - Los Angeles, CA

I have had clients that had trouble getting homeowners insurance because of knob and tube wiring.

Liberty Mutual will insure most homes with knob and tube wiring. But it's been hit an miss.


Sep 08, 2009 02:54 AM

Hi David,

 Thanks for the response. You would probably know yourself that one of the dangers of under size wires that are over protected with a circuit breaker or fuse larger than the capability of the wire itself is a fire waiting to happen. If a certified electrician can evaluate the condition of the knob and tube and whether it is fed with a proper arc fault interrupter or under protected breaker than it may help with the insurance companies. However knob and tube is becoming a obstacle that just needs to be updated today.

                               Best Regards Doug

Smart Move Home Inspection LLC

Sep 09, 2009 12:17 PM

Hi Doug, although I do not live in Ohis, would I still not expect the inspector to realize there is K & T? The guy I had did a lot of "cannot access all spaces" in his comments about wiring. He also indicated we should have GFCI outlets in the kitchen and bath which I understand is not as easily donw with K & T.. that being noted, he slso did not realize there was no insulation in the house. I would appreciate your comments.

Apr 05, 2010 06:19 AM