Replacing knob and tube wiring
Replacing knob and tube wiring
(OP)
Hello,
While conducting minor renovations to a vacant group home, knob and tube wiring was discovered in the ceiling. It is definitely a possibility that other circuits in the group home would also be knob and tube type.
As per Canadian or US Electrical Codes, would it be required to remove only the discovered part of the knob and tube and replace with standard wiring method or would the code mandate replacement of all of the knob and tube type wiring.
On a safety perspective, all of the knob and tube wiring (discovered and undiscovered) should be replaced. I suppose the AHJ would also have a similar requirement. But is there an acceptable and safe scenario, where only the discovered part of knob and tube wiring and circuit is replaced and the remaining part of knob and tube wiring is inspected for insulation deterioration and left in place to be replaced during a major renovation project. Is wiring permit usually approved on partial replacement of knob and tube wiring? Also is there a possibility of safety hazard when the two different type of wiring are present at the same time i.e. knob and tube and standard conduit?
Thank you.
While conducting minor renovations to a vacant group home, knob and tube wiring was discovered in the ceiling. It is definitely a possibility that other circuits in the group home would also be knob and tube type.
As per Canadian or US Electrical Codes, would it be required to remove only the discovered part of the knob and tube and replace with standard wiring method or would the code mandate replacement of all of the knob and tube type wiring.
On a safety perspective, all of the knob and tube wiring (discovered and undiscovered) should be replaced. I suppose the AHJ would also have a similar requirement. But is there an acceptable and safe scenario, where only the discovered part of knob and tube wiring and circuit is replaced and the remaining part of knob and tube wiring is inspected for insulation deterioration and left in place to be replaced during a major renovation project. Is wiring permit usually approved on partial replacement of knob and tube wiring? Also is there a possibility of safety hazard when the two different type of wiring are present at the same time i.e. knob and tube and standard conduit?
Thank you.






RE: Replacing knob and tube wiring
The existing wiring has probably been in service for 60 years or more. Not a bad safety record.
One issue with knob and tube is the lack of a grounding conductor.
However GFI devices depend on sensing the imbalance between the line and the neutral conductors and provide excellent ground fault protection without a grounding conductor.
But, the bottom line:
Discuss this with the AHJ. He has the last say and if he requires changes before he signs off on the structure, there may be insurance coverage implications if the work is not completed to the satisfaction of the AHJ.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Replacing knob and tube wiring
But, this old wiring is so far out-of-spec with today's requirements and safety that (indeed) the only reason it could be considered "usable" or "adequate" now is that "Well, it hasn't failed. Yet." (In Vallejo, CA, I did see bare knob and tube wiring in one house they wanted to sell to us in the mid-80's. Just looking at that was enough for me to immediately walk out of that house and away from that real estate agent, so, you may want to consider replacing it on that re-sale and price reason alone.)
Seriously, unless you absolutely need to maintain the house for historic purposes with that wiring, you need to replace the wiring functionally. And even historic wiring displays could be left as-was, with the new working (energized) wires run out of sight separately. Don't pull the old wires unless you want to salvage the copper. You will find the lights are too few, the number of wall sockets too few, the rating too low, the grounding unsat, the sockets all two-prong, the basic functions for stoves, microwaves, freezers and refrigerators, TV's, computers, etc too low-rated for today's appliances.
RE: Replacing knob and tube wiring
The NEC does not require replacement of knob and tube. Article 394 limits the use of knob and tube to extensions of existing installations in unfinished attics, roof spaces and ceilings, and does not allow Knob and tube where insulation could envelop the conductors.
RE: Replacing knob and tube wiring
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Replacing knob and tube wiring
This might give you some insight.
http://inspectapedia.com/electric/Knob_and_Tube_Wi...
"Will work for (the memory of) salami"
RE: Replacing knob and tube wiring
RE: Replacing knob and tube wiring
I had this stuff in my old house, and was impressed by the workmanship involved. Every connection was carefully twisted, soldered and wrapped. Definitely installed to last.
RE: Replacing knob and tube wiring
RE: Replacing knob and tube wiring
SceneryDriver
RE: Replacing knob and tube wiring
In my area I've not had any problem getting homes with K&T insured, may be different for a group home, idk.