KNOB AND TUBE WIRING
- Thread starter commander
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websparky
Senior Member
- Location
- Cleveland, Ohio
Re: KNOB AND TUBE WIRING
commander,
Yes.
Yes, lots of 'em!
NEC 2002 ARTICLE 394 Concealed Knob-and-Tube Wiring
commander,
Yes.
Yes, lots of 'em!
NEC 2002 ARTICLE 394 Concealed Knob-and-Tube Wiring
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: KNOB AND TUBE WIRING
Allowed but not for new installations other than extending a circuit. Some electricains feel K&T wiring was very safe if properly done. it went away due to high labor costs. Also while it can be properly extended, a homeowner has little knowledge of how to do so per the NEC, so most K&T that is tapped is done wrong (unsafely).
Allowed but not for new installations other than extending a circuit. Some electricains feel K&T wiring was very safe if properly done. it went away due to high labor costs. Also while it can be properly extended, a homeowner has little knowledge of how to do so per the NEC, so most K&T that is tapped is done wrong (unsafely).
karl riley
Senior Member
Re: KNOB AND TUBE WIRING
Tom, I wonder how many electricians are aware of the huge magnetic fields set up by knob and tube. It's curious that someone in a 1920s house may have been getting a higher magnetic field exposure than someone today with all kinds of power usage.
A second thought: would not the 1999 change to 300-3(b) allow knob and tube wiring as long as ferrous metal was not in the circuit?
Karl
Tom, I wonder how many electricians are aware of the huge magnetic fields set up by knob and tube. It's curious that someone in a 1920s house may have been getting a higher magnetic field exposure than someone today with all kinds of power usage.
A second thought: would not the 1999 change to 300-3(b) allow knob and tube wiring as long as ferrous metal was not in the circuit?
Karl
websparky
Senior Member
- Location
- Cleveland, Ohio
Re: KNOB AND TUBE WIRING
Hi Karl,
No.
Hi Karl,
No.
Dave
goldstar
Senior Member
- Location
- New Jersey
- Occupation
- Electrical Contractor
Re: KNOB AND TUBE WIRING
From a safety point of view, when you find circuits that are knob and tube wired I would convert those circuits over to GFCI protection in accordance with 406.3(D)(3)(a),(b) & (c).
You're also probably better off using a GFCI breaker rather than individual GFCI receptacles. The reason being is that (way back) when these circuits were installed they probably didn't "cascade" the wiring from one receptacle to another (as we do today) but rather ran the feeders down the center of a hallway or above a room and tapped and soldered the wires on and dropped down to pick up a receptacle. Finding the start of the run is often difficult.
Also, if you're doing a job that is a renovation or an "add-on" and you run into a lot of K & T that might be left in place in some sections, make sure you mark both ends of the wires before you cut them (i.e. A-A, B-B, etc). That way you'll know what has to be reconnected to what. Most of these wires have lost their color over the years and it's difficult to determine which is hot and neutral (unless you drag a grounded wire around with you).
At the last job I ran into with K & T the builder called me in a panic and said "We have a lot of knob and tube wires. What should I do"? So I explained how to mark each wire and cut it. When I got there the next morning the hallways were gutted, bedrooms on both sides remained in tact and there were about 20 wires hanging down in the hallways with no markings. It took several days to trace out what was supposed to go with what and what circuits they were on.
Good luck with this !!
From a safety point of view, when you find circuits that are knob and tube wired I would convert those circuits over to GFCI protection in accordance with 406.3(D)(3)(a),(b) & (c).
You're also probably better off using a GFCI breaker rather than individual GFCI receptacles. The reason being is that (way back) when these circuits were installed they probably didn't "cascade" the wiring from one receptacle to another (as we do today) but rather ran the feeders down the center of a hallway or above a room and tapped and soldered the wires on and dropped down to pick up a receptacle. Finding the start of the run is often difficult.
Also, if you're doing a job that is a renovation or an "add-on" and you run into a lot of K & T that might be left in place in some sections, make sure you mark both ends of the wires before you cut them (i.e. A-A, B-B, etc). That way you'll know what has to be reconnected to what. Most of these wires have lost their color over the years and it's difficult to determine which is hot and neutral (unless you drag a grounded wire around with you).
At the last job I ran into with K & T the builder called me in a panic and said "We have a lot of knob and tube wires. What should I do"? So I explained how to mark each wire and cut it. When I got there the next morning the hallways were gutted, bedrooms on both sides remained in tact and there were about 20 wires hanging down in the hallways with no markings. It took several days to trace out what was supposed to go with what and what circuits they were on.
Good luck with this !!
karl riley
Senior Member
Re: KNOB AND TUBE WIRING
Dave, your Code reference is correct, of course. But hang with me a minute, because I am bothered by the 1999 change, which appears to me a step backward.
What now prevents you from running two NM circuits to some loads and using the hot from one cable and the neutral from the other cable, just as the knob and tube wiring ran? This is no longer K&T on insulators,so it is not banned by that article.
What do you think?
Karl
Dave, your Code reference is correct, of course. But hang with me a minute, because I am bothered by the 1999 change, which appears to me a step backward.
What now prevents you from running two NM circuits to some loads and using the hot from one cable and the neutral from the other cable, just as the knob and tube wiring ran? This is no longer K&T on insulators,so it is not banned by that article.
What do you think?
Karl
Re: KNOB AND TUBE WIRING
Karl,
Would the use of only one conductor of a NM cable satify 300.1 and 300.3(B) ? Note 300.3(B)(3).
What should be done with the unused conductor of each NM cable to prevent capacitive coupling and the associated voltage 'build-up'?
Karl,
Would the use of only one conductor of a NM cable satify 300.1 and 300.3(B) ? Note 300.3(B)(3).
What should be done with the unused conductor of each NM cable to prevent capacitive coupling and the associated voltage 'build-up'?
websparky
Senior Member
- Location
- Cleveland, Ohio
Re: KNOB AND TUBE WIRING
Hi Karl,
Would it still not be "Open wiring on insulators"?
OR, am I missing your question?
Typically, an accepted method when one runs into this type of wiring, is to convert as soon as practical to another method such as NM or MC or EMT. If only one wire is available or needs to be extended, then the proprer splice needs to be applied and the extention made.
Hope this helps,
Dave
Hi Karl,
Would it still not be "Open wiring on insulators"?
OR, am I missing your question?
Typically, an accepted method when one runs into this type of wiring, is to convert as soon as practical to another method such as NM or MC or EMT. If only one wire is available or needs to be extended, then the proprer splice needs to be applied and the extention made.
Hope this helps,
Dave
karl riley
Senior Member
Re: KNOB AND TUBE WIRING
GWZ and Dave, Don't get me wrong, I am not advocating running two Romex circuits to a load and using the hot from one and the neutral from the other. I am concerned that the 1999 & 2002 change to 300-3(B) seem to allow this, even though it is obviously not good practice.
Romex is not "open conductors on insulators", Dave. K&T is single conductors run on porcelin insulators. Romex is not "open" and is stapled. Right?
This is not purely speculation. When two-conductor travelers are used with three-way light circuits, this is exactly what may be the case.
So once again, does anyone see a violation of 2002 Code here, assuming the two circuits enter the panel box under one clamp?
Karl
GWZ and Dave, Don't get me wrong, I am not advocating running two Romex circuits to a load and using the hot from one and the neutral from the other. I am concerned that the 1999 & 2002 change to 300-3(B) seem to allow this, even though it is obviously not good practice.
Romex is not "open conductors on insulators", Dave. K&T is single conductors run on porcelin insulators. Romex is not "open" and is stapled. Right?
This is not purely speculation. When two-conductor travelers are used with three-way light circuits, this is exactly what may be the case.
So once again, does anyone see a violation of 2002 Code here, assuming the two circuits enter the panel box under one clamp?
Karl
websparky
Senior Member
- Location
- Cleveland, Ohio
Re: KNOB AND TUBE WIRING
Hi Karl,
Is this what you meant?
Dave
Hi Karl,
Is this what you meant?
Trying to follow..........
Dave
Re: KNOB AND TUBE WIRING
Karl, this is an extension of our discussion of July 7 I think,
Now as far as only using part of the conductors of a circuit, I.E. switch loop (EMF negated) or travelers and no neutral (EMF possibly rampant), this is perfectly legal as far as code. The EMF issue is not addressed at this time in the NEC, that is why people such as yourself and the other aware and knowledgable people here are going to bring it to their attention.
Roger
Karl, this is an extension of our discussion of July 7 I think,
300.3(b).
Now as far as only using part of the conductors of a circuit, I.E. switch loop (EMF negated) or travelers and no neutral (EMF possibly rampant), this is perfectly legal as far as code. The EMF issue is not addressed at this time in the NEC, that is why people such as yourself and the other aware and knowledgable people here are going to bring it to their attention.
Roger
- Location
- Illinois
- Occupation
- retired electrician
Re: KNOB AND TUBE WIRING
Roger,
What about 300.3(B)(3)? This section acts as an exception to the main part of the rule in 300.3(B).
Don
Roger,
What about 300.3(B)(3)? This section acts as an exception to the main part of the rule in 300.3(B).
Don
karl riley
Senior Member
Re: KNOB AND TUBE WIRING
Dave, 330.3(b)3 refers NM cable in non-ferrous boxes to 300.20(B). Very confusing!
300.20(B) says that if the single conductor passes through a ferrous box or plate, you have to cut a slot between it and the other conductor of the circuit. That's why I mentioned that the two circuits would have to pass into the panel under the same clamp.
So 300.20 provides the exception to 300.3(B) for NM. I think this is unfortunate and I would be interested to know why the 1999 Code committee provided this loophole. A step backwards.
Karl
Dave, 330.3(b)3 refers NM cable in non-ferrous boxes to 300.20(B). Very confusing!
300.20(B) says that if the single conductor passes through a ferrous box or plate, you have to cut a slot between it and the other conductor of the circuit. That's why I mentioned that the two circuits would have to pass into the panel under the same clamp.
So 300.20 provides the exception to 300.3(B) for NM. I think this is unfortunate and I would be interested to know why the 1999 Code committee provided this loophole. A step backwards.
Karl
karl riley
Senior Member
Re: KNOB AND TUBE WIRING
Roger, the Code does recognize the inductive effect of electromagnetic fields for it's heating effect on ferrous metal. But as we know it does not concern itself with the inductive effects on electronic instruments, and it is nowhere near being able to deal with controversial health effects.
Too bad it couldn't allow NM to stay under the protection of 300.3(b), which is a corner stone of good wiring.
About 2005, I can't even download the suggested changes. It comes out in strange characters!
Karl
Roger, the Code does recognize the inductive effect of electromagnetic fields for it's heating effect on ferrous metal. But as we know it does not concern itself with the inductive effects on electronic instruments, and it is nowhere near being able to deal with controversial health effects.
Too bad it couldn't allow NM to stay under the protection of 300.3(b), which is a corner stone of good wiring.
About 2005, I can't even download the suggested changes. It comes out in strange characters!
Karl
Re: KNOB AND TUBE WIRING
Karl, have you tried saving the file into a folder and then opening it? Let us know , someone will get you into it.
Don,
We could also use Kirchoff's current and voltage laws for the circuit definition.
Circuit, for this discussion will be a path for current to leave the source, complete a task, and return to source. IMO 300.3(B)(3) would not be an exception to allow conductors of different circuits to be used to create a circuit. This would enter into an area somewhere around common neutral or fouled multiple circuits.
Roger
Karl, have you tried saving the file into a folder and then opening it? Let us know , someone will get you into it.
Don,
I would argue this, and ask if you might agree with a simple definition of circuit.
We could also use Kirchoff's current and voltage laws for the circuit definition.
Circuit, for this discussion will be a path for current to leave the source, complete a task, and return to source. IMO 300.3(B)(3) would not be an exception to allow conductors of different circuits to be used to create a circuit. This would enter into an area somewhere around common neutral or fouled multiple circuits.
Roger
websparky
Senior Member
- Location
- Cleveland, Ohio
Re: KNOB AND TUBE WIRING
Karl,
Now I'm following you!
If in the above scenario, two legs of a threeway traveler or two legs plus the the line or load would equal two or three conductors. In that case, to avoid the heating effect, one could use 12/3-WG NM from the closest available splice point and have all conductors entering one KO and eliminate the heating effect in that one box. No?
IMO;
The amount of current flow on this portion of the entire circuit that feeds the fixture would be rather low. That combined with the minimal amount of voltage present and the relative heat dissipation, I wonder how much effect it would have overall?
Maybe someone could point us to a formula that we could use to calculate the effect?
Thanks,
Dave
Karl,
Now I'm following you!
If in the above scenario, two legs of a threeway traveler or two legs plus the the line or load would equal two or three conductors. In that case, to avoid the heating effect, one could use 12/3-WG NM from the closest available splice point and have all conductors entering one KO and eliminate the heating effect in that one box. No?
IMO;
The amount of current flow on this portion of the entire circuit that feeds the fixture would be rather low. That combined with the minimal amount of voltage present and the relative heat dissipation, I wonder how much effect it would have overall?
Maybe someone could point us to a formula that we could use to calculate the effect?
Thanks,
Dave
websparky
Senior Member
- Location
- Cleveland, Ohio
Re: KNOB AND TUBE WIRING
Karl,
Let me know what type of file you can open and if possible which section you need, and I'll convert one for you. The whole thing is rather large and is broken up into several .pdf files.
Dave
Karl,
Let me know what type of file you can open and if possible which section you need, and I'll convert one for you. The whole thing is rather large and is broken up into several .pdf files.
Dave
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