Knob and Tube Connectors
- Thread starter physis
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ty
Senior Member
- Location
- 3rd Rock from the Sun
Re: Knob and Tube Connectors
If something shorted the Hot (to say, metal lath, for example), you might find that someone has switched the Hot and Neutral in the panel.
Sometimes you have to be careful.
If something shorted the Hot (to say, metal lath, for example), you might find that someone has switched the Hot and Neutral in the panel.
sandsnow
Senior Member
- Location
- Southern California
Re: Knob and Tube Connectors
Al
Great excerpt from the white book. I did not know that.
I retract my "holy grail" statement about new equipment not being listed for k&t
Al
Great excerpt from the white book. I did not know that.
I retract my "holy grail" statement about new equipment not being listed for k&t
Re: Knob and Tube Connectors
Excellent interface for romex wire.
Peter D's way works great if you need to go to BX, MC, AC, EMT, IMC, GRC, PVC, etc.
Use a 4" square plastic box--carlon B432, blank cover A400. If you don't have loom, use a piece of romex sheath. Slide into box, under clamp.Originally posted by peter d:
It's been a while, but this is how I do it. I use plain old NM connectors, cut a piece of the K&T loom, slide it over the K&T conductor, and then put the whole assembly into the rx connector, which is conveniently attached to a 4" square box.
Excellent interface for romex wire.
Peter D's way works great if you need to go to BX, MC, AC, EMT, IMC, GRC, PVC, etc.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Re: Knob and Tube Connectors
You literally have a reference hot, neutral, and ground in your hand.
Suggestion: A wiggie and an extension cord (in a known-properly-wired receptacle) make great a diagnostic-tool combination.
You literally have a reference hot, neutral, and ground in your hand.
physis
Senior Member
Re: Knob and Tube Connectors
The reason I ask is the metal box conundrum. Like Bob points out, 300.20.
I'd really like to see a demonstration of this inductive heating from two 15 or 20 amp conductors passing through a 1/16" box wall. But I don't write this stuff.
There are a lot of cases where plastic just isn't my favorite choise. Peter and Romeo mentioned my favorite, that doesn't comply, but that's still what I think is best.
Al brought up 300.20(B). I hadn't thought about it applying to a box but it looks like it does.
Edit: I think keyboard caused character drops where Error D
[ January 20, 2006, 05:06 PM: Message edited by: physis ]
The reason I ask is the metal box conundrum. Like Bob points out, 300.20.
I'd really like to see a demonstration of this inductive heating from two 15 or 20 amp conductors passing through a 1/16" box wall. But I don't write this stuff.
There are a lot of cases where plastic just isn't my favorite choise. Peter and Romeo mentioned my favorite, that doesn't comply, but that's still what I think is best.
Al brought up 300.20(B). I hadn't thought about it applying to a box but it looks like it does.
Edit: I think keyboard caused character drops where Error D
[ January 20, 2006, 05:06 PM: Message edited by: physis ]
sandsnow
Senior Member
- Location
- Southern California
Re: Knob and Tube Connectors
You also have the 300.16(A) issue which requires a seperately bushed hole for each conductor. Unless you have a special fitting which looks like a straight weatherhead (service entrance cap that goes on top of a raceway).
What the heck are you doing anyway??
You also have the 300.16(A) issue which requires a seperately bushed hole for each conductor. Unless you have a special fitting which looks like a straight weatherhead (service entrance cap that goes on top of a raceway).
What the heck are you doing anyway??
physis
Senior Member
Re: Knob and Tube Connectors
Hi Larry,
This doesn't come from anything impractical that I'm doing right now. I work with K&T a lot and I just kinda don't get why it seems like there's an accepted allowance for code violations with this.
I wasn't aware of a legal method for going to a metal box with K&T until Al pointed out that you can use 300.20(B) and take a hack saw to the box.
Romeo has a legal solution with going to a plastic box first. Not usually all that practical though.
And I might as well gripe about some code language a little.
300.16. A box or terminal fitting having separately bushed holes for each conductor.......
Does that mean you can use a box period or that a box must also have separately bushed holes for each conductor?
What's a terminal fitting? I hope I'm not missing something obvious here but I'm trying to imagine all kinds of goofy things that a terminal fitting might be and I don't get it unless maybe I assume it's a connector. Either that or a wire lug, I don't think it's that.
Are there any connectors available with two separately bushed holes? I've never seen any.
Why does 300.20 address "phase" conductors instead of ungrounded conductors? That's pretty wierd language. Does phase conductors include ungrounded single phase conductor? I'd think it would but then why not call the things ungrounded conductors?
But it's not the code language I'm concerned with so much. It's that code violations seem to be commonly accepted. I'd say safe for the most part as well.
So should the code have some broader allowances for terminating K&T to metal boxes?
Hi Larry,
This doesn't come from anything impractical that I'm doing right now. I work with K&T a lot and I just kinda don't get why it seems like there's an accepted allowance for code violations with this.
I wasn't aware of a legal method for going to a metal box with K&T until Al pointed out that you can use 300.20(B) and take a hack saw to the box.
Romeo has a legal solution with going to a plastic box first. Not usually all that practical though.
And I might as well gripe about some code language a little.
300.16. A box or terminal fitting having separately bushed holes for each conductor.......
Does that mean you can use a box period or that a box must also have separately bushed holes for each conductor?
What's a terminal fitting? I hope I'm not missing something obvious here but I'm trying to imagine all kinds of goofy things that a terminal fitting might be and I don't get it unless maybe I assume it's a connector. Either that or a wire lug, I don't think it's that.
Are there any connectors available with two separately bushed holes? I've never seen any.
Why does 300.20 address "phase" conductors instead of ungrounded conductors? That's pretty wierd language. Does phase conductors include ungrounded single phase conductor? I'd think it would but then why not call the things ungrounded conductors?
But it's not the code language I'm concerned with so much. It's that code violations seem to be commonly accepted. I'd say safe for the most part as well.
So should the code have some broader allowances for terminating K&T to metal boxes?
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Knob and Tube Connectors
300.16(A) is an interesting animal. The last sentence in it offers an important clue:
The "fitting" is where the cable sheath or raceway ends and the internal conductors continue.
The fitting is directly analogous to a service weatherhead, only smaller and needing only to be suitable for dry locations away from direct sunlight. Two of the old slang names for the fitting were monkey face or birds foot.
The conductor emerging from the raceway or cable splices to the open wiring or concealed K&T with a "flying splice" using "approved slicing devices" - see 394.56. - that is wire nuts, among other things.
300.16(A) is an interesting animal. The last sentence in it offers an important clue:
300.16(A) is the exception to the rule: "All splices go in boxes."
The "fitting" is where the cable sheath or raceway ends and the internal conductors continue.
The fitting is directly analogous to a service weatherhead, only smaller and needing only to be suitable for dry locations away from direct sunlight. Two of the old slang names for the fitting were monkey face or birds foot.
The conductor emerging from the raceway or cable splices to the open wiring or concealed K&T with a "flying splice" using "approved slicing devices" - see 394.56. - that is wire nuts, among other things.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Knob and Tube Connectors
Courtesy of Electricmanscot and ECN: Note there are three "fittings" in the photo.
Courtesy of Electricmanscot and ECN: Note there are three "fittings" in the photo.
sandsnow
Senior Member
- Location
- Southern California
Re: Knob and Tube Connectors
YES
Al,
That's what I was thinking of. Good luck finding any I would think. DO they still make them.
As far as the metal boxes and the slots. Someone posted, here I think (maybe ECN), that the older versions of the Code allowed seperate holes in ferrous metal enclosures when under 50 amps. I don't have any dates or more details on that. In seems 300.16 may be a hold over and just forgotten. Who knows?
YES
Al,
That's what I was thinking of. Good luck finding any I would think. DO they still make them.
As far as the metal boxes and the slots. Someone posted, here I think (maybe ECN), that the older versions of the Code allowed seperate holes in ferrous metal enclosures when under 50 amps. I don't have any dates or more details on that. In seems 300.16 may be a hold over and just forgotten. Who knows?
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Knob and Tube Connectors
In a pinch, I contend, that if I take a 1/2" weatherhead that is threaded for 1/2" NPT, I can screw into that female the connector or my choice.
Say, for romex, I could screw in a plain old 3/8" two screw romex clamp (sans locknut).
The clamp secures the end of the sheath and the conductors emerge from the "fitting" through the black bakelite of the weatherhead.
In a pinch, I contend, that if I take a 1/2" weatherhead that is threaded for 1/2" NPT, I can screw into that female the connector or my choice.
Say, for romex, I could screw in a plain old 3/8" two screw romex clamp (sans locknut).
The clamp secures the end of the sheath and the conductors emerge from the "fitting" through the black bakelite of the weatherhead.
wireman3736
Senior Member
- Location
- Vermont/Mass.
Re: Knob and Tube Connectors
Something is missing here, there's something in the NEC about grounding the metal box, some people are so forgetful.
Something is missing here, there's something in the NEC about grounding the metal box, some people are so forgetful.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Knob and Tube Connectors
In many single family dwellings the walls, floors and ceilings are non-conductive. 250.110(1) has application, upon occasion, and describes how the box actually can be left ungrounded.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Knob and Tube Connectors
Leaving a metal j-box ungrounded when connected to K&T occurs most commonly, in my experience, when I have to cut in a box to support a new luminaire. When the luminaire location is already supplied by existing K&T, and the old fixture was screwed to the plaster and lathe, I am bound to install a box when I replace the luminaire with a modern luminaire.
In most spaces, the luminaire location is more than 5 feet horizontally and 8 feet vertically from a grounded surface, and 250.110(1) applies nicely.
Leaving a metal j-box ungrounded when connected to K&T occurs most commonly, in my experience, when I have to cut in a box to support a new luminaire. When the luminaire location is already supplied by existing K&T, and the old fixture was screwed to the plaster and lathe, I am bound to install a box when I replace the luminaire with a modern luminaire.
In most spaces, the luminaire location is more than 5 feet horizontally and 8 feet vertically from a grounded surface, and 250.110(1) applies nicely.
wireman3736
Senior Member
- Location
- Vermont/Mass.
Re: Knob and Tube Connectors
Sorry Al but I'll have to disagree with you on 250.110 (1). This is not an exception to grounding, It's telling you if it falls within these dimensions that it shall be grounded, just because it's above 8' doesn't allow it to override other sections of the code. Article 250.112 (J) sends you to part 5 in article 410, Article 410.18 settles this argument.I know it's common practice to replace metallic fixtures on ungrounded circuits with new metallic fixtures but it doesn't meet code without GFCI protection.
Sorry Al but I'll have to disagree with you on 250.110 (1). This is not an exception to grounding, It's telling you if it falls within these dimensions that it shall be grounded, just because it's above 8' doesn't allow it to override other sections of the code. Article 250.112 (J) sends you to part 5 in article 410, Article 410.18 settles this argument.I know it's common practice to replace metallic fixtures on ungrounded circuits with new metallic fixtures but it doesn't meet code without GFCI protection.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Knob and Tube Connectors
Air, distance and non-conductive building materials make a good insulation from ground, especially in a wood framed dwelling with plaster on wood lathe and a wood floor. The most common grounded surfaces that might be in that room will be the cast iron radiator and its pipes, or metal grating in contact with metal ductwork.
250.110(1) spells out the distances within which grounding is required. Outside of those distances, grounding may, or may not, be done. . .it's just not required to be done.
On the contrary, as I read 410.18, I read it as having two minds. One is as you describe, and the other is as I describe.
410.18 says it can be grounded or ungrounded.
Air, distance and non-conductive building materials make a good insulation from ground, especially in a wood framed dwelling with plaster on wood lathe and a wood floor. The most common grounded surfaces that might be in that room will be the cast iron radiator and its pipes, or metal grating in contact with metal ductwork.
250.110(1) spells out the distances within which grounding is required. Outside of those distances, grounding may, or may not, be done. . .it's just not required to be done.
Riograndeelectric
Senior Member
- Location
- Lakewood Colorado
Re: Knob and Tube Connectors
since when is it legal to make an extension
from
an ungrounded system or to add a new device or fixture that is required tobe grounded. I see this all the time here in colorado.the Home owner or the DIY adds new duplex recpticel
or a new light fixture climbs in the attic cuts the K&T and splice a pice of 2 wire nm cable to he K&T then adds
the duplex or light fixture.
you are making a tap from an ungrounded system
I see this alot on the old 2 wire black rigid pipe jobs too.
since when is it legal to make an extension
from
an ungrounded system or to add a new device or fixture that is required tobe grounded. I see this all the time here in colorado.the Home owner or the DIY adds new duplex recpticel
or a new light fixture climbs in the attic cuts the K&T and splice a pice of 2 wire nm cable to he K&T then adds
the duplex or light fixture.
you are making a tap from an ungrounded system
I see this alot on the old 2 wire black rigid pipe jobs too.
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