Working with Knobs and Tubes Electrical Installations

It hasn't been legal to repair Knob and Tube in a long time. The only place it was legal for repairs or new work was in barns and similar outbuildings.

BTW, round 'Romex' will usually pass through the hole after the tubes are pulled out.

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Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

As I recall, without going for the Code book, it requires a zinc rod.

Or copper plated steel. It depends on the soil.

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Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

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                          Wayne Watson (Nevada City, CA)

                        Web Page:

Two things occurred yesterday that'll impact my story. I ran into a contractor buddy who has dealt with KnT here in our small community in the Sierra foothills. He's done this work before, and gave me some useful tips. More importantly, I finally got to talk to my son about this. His first message was through my wife. Ahem! He's not expecting me to rewire the whole place. What he's doing is re-modeling the kitchen, and wants two outlets moved, and possibly a new one put in.

My buddy, aside from providing some electrical hints, suggested if lots of work is needed to find someone here that does such work, and hire them to go to SF to do the work. The building market is suffering, and contractors are looking for work where they can get it. They can probably get good money in SF for more than here, but less than a SF contractor. We are 150 miles from SF.

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                          Wayne Watson (Nevada City, CA)

                        Web Page:

Knob and tube wiring, if it has not been abused, is not automatically dangerous. Splices are twisted and taped, but they are also soldered. I have seen only one K&T splice fail (it was a ?cold? solder joint from the start). If the wiring has been properly fused, current is no more problem than it is for any other type of wiring. See also the last point below.

There certainly are some virtues in replacing it, but entirely replacing K&T wiring is *very* expensive.

As ehsjr said, one code acceptable method is using GFCI protection for grounding type outlets (could just be a GFCI outlet). The outlet has to be marked as Ed details.

A ?ground? wire may be added and a grounded outlet installed. For this purpose, the ?ground? wire does not have to be routed with the other wires.

In the past the added ?ground? wire could be connected to a metal water pipe. That is no longer permitted. They now have to be connected to anywhere on the ?grounding electrode system?, which includes the panel ground bar, the heavy conductors to the grounding electrodes, the first

5 ft of water pipe inside the building if the water pipe is used as a grounding electrode (the service connection to the pipe should then be in the same 5 ft.).

Water pipe, at least 10 ft buried, has been required to be used as a grounding electrode for a very long time. More recently, because water service pipe can be replaced with copper, a ?supplemental? electrode has been required. A ground rod is the easiest to install. A municipal metal water system will have a much lower resistance to earth than a rod. The code does not require old systems to add a rod unless ?additional? work is done. The code now usually requires an additional ?concrete encased electrode? for new construction.

?Ground? wires are not allowed to be attached only to isolated ground rods. As Mark said, this is a major safety hazard. Assume your metal case ?grounded? drill develops a short from hot to case. The ground current flows to the ground rod. Further assume the ground rod is not only the code acceptable 25 ohms (with 2 rods it can be any resistance) by a very good 12 ohms. There is 10 amps added. Depending on the other load on the circuit, the fuse/breaker will open in a little while to never. In the meantime you are connected to the hot wire holding the drill.

A major function of the ?ground? wire is to cause a high current to flow on a short to open the fuse/breaker. The path is ?ground? wire to service panel, through the required neutral-ground bond, and through the service neutral to the supply transformer. Earth is not permitted to be a part of the path.

Some insurance companies in some areas do not insure houses with K&T wiring. Phil Munro posted 2 links on the subject:

is a report to the Illinois Department of Commerce and Community Affairs on adding building insulation around existing K&T wiring. No record of hazard was found in the large number of K&T installations that had insulation added around them. The second link appears to no longer be online - was the record of a complaint to the Maine state Bureau of Insurance by a homeowner against an insurance company. The insurance company denied renewal of a policy based on K&T wiring. The insurance company was ordered to renew the policy because the insurance company "provided no justification for its position that knob and tube wiring per se automatically provides grounds for nonrenewal".

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bud--