Re feeding knob and tube wiring

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mkgrady

Senior Member
Location
Massachusetts
I run into a lot of old knob and tube wiring in house remodel jobs. I usually just remove it and re wire what it is serving but in this case it feeds a part of the house that is not being renovated. I plan to run a new circuit from the main panel to the knob and tube where it is exposed in the basement but I don't know how to make the transition from Romex to the k&t. What parts do I need to make the splice?
 

jaylectricity

Senior Member
Location
Massachusetts
Occupation
licensed journeyman electrician
It helps if you have the little tube things that go around the conductor as it enters a box. Do not reroute the k&t. Everything must stay as installed except for the last 12" or so that will go into the box you'll refeed. You can put a non-metallic box, put the conductors into separate entrances, then bring the romex to another entrance.

If you wanted to, use a metal box with internal clamps, and run each of the k&t conductors in each of the holes. Then bring the romex in through the other clamp, or through a knockout with a connector of your preference.

The real key is to have the box as close to the two knobs for each conductor as possible because you can't staple them to bring them to another location, even though you might rather have the box in a specific place.

Also, I've used stackers to support the conductors right before they enter the box, but that's up to you or the AHJ.
 

mkgrady

Senior Member
Location
Massachusetts
It helps if you have the little tube things that go around the conductor as it enters a box. Do not reroute the k&t. Everything must stay as installed except for the last 12" or so that will go into the box you'll refeed. You can put a non-metallic box, put the conductors into separate entrances, then bring the romex to another entrance.

If you wanted to, use a metal box with internal clamps, and run each of the k&t conductors in each of the holes. Then bring the romex in through the other clamp, or through a knockout with a connector of your preference.

The real key is to have the box as close to the two knobs for each conductor as possible because you can't staple them to bring them to another location, even though you might rather have the box in a specific place.

Also, I've used stackers to support the conductors right before they enter the box, but that's up to you or the AHJ.

Thanks. That's helpful. I have been saving some of that fibrous tube stuff for this, just wasn't sure what to do with it. I actually expect the inspector will tell me I can't connect to k&t. He makes his own rules.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
As to how to make the connection once inside the box, you would need a currently approved connector (wire nut, wago, Polaris) which can handle the two wire sizes involved.
Do not solder the connection as you would with repaired connections within existing legacy K&T.
 

jaylectricity

Senior Member
Location
Massachusetts
Occupation
licensed journeyman electrician
Also, you'll need arc-fault protection as you'll most likely be altering the circuit by more than six feet, but you should really use a dual function afci/gfci breaker.

I suppose you could feed it right next to the panel and possibly not be required to arc-fault it.
 

mkgrady

Senior Member
Location
Massachusetts
Also, you'll need arc-fault protection as you'll most likely be altering the circuit by more than six feet, but you should really use a dual function afci/gfci breaker.

I suppose you could feed it right next to the panel and possibly not be required to arc-fault it.

Not that I would do it but technically could I extend the k&t towards the panel utilizing the old knobs and tubes to avoid an extension under 6 feet and avoid the afci protection? Really I would not do this but I'm trying to understand what k&t is usable as is or as modified. The inspector here believe all k&t must be removed once it is exposed. I don't believe that is true.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Not that I would do it but technically could I extend the k&t towards the panel utilizing the old knobs and tubes to avoid an extension under 6 feet and avoid the afci protection? Really I would not do this but I'm trying to understand what k&t is usable as is or as modified. The inspector here believe all k&t must be removed once it is exposed. I don't believe that is true.
Totally not in the NEC AFAIK, but there may be a local amendment involved.
It is, however good practice.
And if only one endcis exposed it would not seem to justify complete removal of all downstream K&T.
 

david

Senior Member
Location
Pennsylvania
If you wanted to, use a metal box with internal clamps, and run each of the k&t conductors in each of the holes. Then bring the romex in through the other clamp, or through a knockout with a connector of your preference.

metal box with internal clamps, run each of the k&t conductors in each of the holes./QUOTE]

I do not believe this is correct since you did not mention how to deal with the metal between the un-grounded and neutral
conductors. If running the knob and tube conductors through separate holes does not create a situation where there would be metal between the conductors than i am mistaken. If however there is metal between the conductors you would need to cut a slot to allow the magnetic fields to pass through.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
metal box with internal clamps, run each of the k&t conductors in each of the holes./QUOTE]

I do not believe this is correct since you did not mention how to deal with the metal between the un-grounded and neutral
conductors. If running the knob and tube conductors through separate holes does not create a situation where there would be metal between the conductors than i am mistaken. If however there is metal between the conductors you would need to cut a slot to allow the magnetic fields to pass through.
The slot is needed to keep magnetic fields from surrounding the two conductors, not to "let the field pass through".
 

jaylectricity

Senior Member
Location
Massachusetts
Occupation
licensed journeyman electrician
Not that I would do it but technically could I extend the k&t towards the panel utilizing the old knobs and tubes to avoid an extension under 6 feet and avoid the afci protection? Really I would not do this but I'm trying to understand what k&t is usable as is or as modified. The inspector here believe all k&t must be removed once it is exposed. I don't believe that is true.

It's tough to make k&t look existing with used parts. The inspector can believe all he wants, but if it was legal when it was installed it doesn't have to come out for any reason.

I do not believe this is correct since you did not mention how to deal with the metal between the un-grounded and neutral
conductors. If running the knob and tube conductors through separate holes does not create a situation where there would be metal between the conductors than i am mistaken. If however there is metal between the conductors you would need to cut a slot to allow the magnetic fields to pass through.

The slot is needed to keep magnetic fields from surrounding the two conductors, not to "let the field pass through".

I hear you both and I understand, but just about every light fixture ever hung on a knob&tube circuit is hung on a box where the individual conductors run through separate holes in a metal box. Every receptacle resides in a metal box where the conductors come in through separate holes.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
It's tough to make k&t look existing with used parts. The inspector can believe all he wants, but if it was legal when it was installed it doesn't have to come out for any reason.

In Michigan, if a wall is opened (like during a re-mod) all the electrical in that wall must be brought up to current code. It's a Michigan Building Code thing, not an NEC thing, but we still have to do it. So if K&T is exposed during a re-mod here, it must be replaced.
 

david

Senior Member
Location
Pennsylvania
It's tough to make k&t look existing with used parts. The inspector can believe all he wants, but if it was legal when it was installed it doesn't have to come out for any reason.





I hear you both and I understand, but just about every light fixture ever hung on a knob&tube circuit is hung on a box where the individual conductors run through separate holes in a metal box. Every receptacle resides in a metal box where the conductors come in through separate holes.

Actually I seldom remember finding a ?junction? box for ceiling fixture for knob and tube when the wiring method was left in it original condition. Most fixtures supplied by knob and tube wiring methods that I have seen just have the conductors knobbed on the ceiling joist and the conductors just come through a hole in the lath and plaster.
 

iwire

Moderator
Staff member
Location
Massachusetts
I do not believe this is correct since you did not mention how to deal with the metal between the un-grounded and neutral conductors. If running the knob and tube conductors through separate holes does not create a situation where there would be metal between the conductors than i am mistaken. If however there is metal between the conductors you would need to cut a slot to allow the magnetic fields to pass through.

Strangely the NEC requires the K&T to be brought into the box through separately bushed holes.


300.16 Raceway or Cable to Open or Concealed Wiring.

(A) Box, Conduit Body, or Fitting. A box, conduit body, or terminal fitting having a separately bushed hole for each conductor shall be used wherever a change is made from conduit, electrical metallic tubing, electrical nonmetallic tubing, nonmetallic-sheathed cable, Type AC cable, Type MC cable, or mineral-insulated, metal-sheathed cable and surface raceway wiring to open wiring or to concealed knob-and-tube wiring. A fitting used for this purpose shall contain no taps or splices and shall not be used at luminaire outlets. A conduit body used for this purpose shall contain no taps or splices, unless it complies with 314.16(C)(2).

I have never seen anyone cut the slot for K&T yet I agree the code requires it.
 

romex jockey

Senior Member
Location
Vermont
Occupation
electrician
KaaaTeee

KaaaTeee

K&T interfacing just got a tad easier in the '14>>>>

250.130 C (4) An? equipment grounding conductor that is part of an-
other branch circuit that originates from the enclosure
where the branch circuit for the receptacle or branch
circuit originates

Other than that, it's still basically as user friendly as threading a needle with an oyster.....:)


~RJ~
 

mkgrady

Senior Member
Location
Massachusetts
K&T interfacing just got a tad easier in the '14>>>>



Other than that, it's still basically as user friendly as threading a needle with an oyster.....:)


~RJ~
I wish I had some idea what you mean by any of that.

I wish I could just buy a kit that contains the parts I need to splice the old k&t to a new branch circuit.
 

jaylectricity

Senior Member
Location
Massachusetts
Occupation
licensed journeyman electrician
Actually I seldom remember finding a ?junction? box for ceiling fixture for knob and tube when the wiring method was left in it original condition. Most fixtures supplied by knob and tube wiring methods that I have seen just have the conductors knobbed on the ceiling joist and the conductors just come through a hole in the lath and plaster.

Well sure, if there are devices and fixtures tied to the knob and tube in the open walls, those must be rectified. But if the knob and tube wiring just passes through the wall to another room, you don't cut it just to refeed it. You'd be adding additional splices that just complicate the issue. Better to leave it be.
 

PetrosA

Senior Member
Here in town there are a lot of K+T installs still in use and supply houses still stock 3" pancakes with K+T clamps in them, but I haven't seen any 4" rounds or pancakes or larger boxes with K+T clamps. They also stock rubber grommets to fit a 1/2 inch KO.

I've never seen K+T enter a metal wall case, pancake or fuse box (which were the only metal boxes used with K+T) with a slit cut in the box between the wires. I personally wouldn't have any problem using a 1900 box (4 square for you yung'ins) with two rubber grommets for the K+T in neighboring KOs. The rubber grommet would fulfill the same role as the porcelain grommets used originally and should be available to fit the loom you have. If your supply house doesn't carry them, you can get variety boxes dirt cheap at Harbor Freight.
 
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