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#6928 - 01/15/02 11:27 PM Old NM cable, stranded ground.  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
I stumbled across some old, cloth covered, rubber insulated NM cable today. It had a stranded ground inside. Can anyone date this, or otherwise comment?
While on the subject of OLD work, has anyone considered using hi-temp insulated sleeving over 60C NM to boost it's temp. rating, thereby allowing installation of fixtures requiring 90C supply conductors?
This has been suggested in a book on old wiring and how to deal with it.


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#6929 - 01/16/02 07:07 AM Re: Old NM cable, stranded ground.  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,306
possibly a David Shapiro book?


#6930 - 01/16/02 07:51 AM Re: Old NM cable, stranded ground.  
George Corron  Offline
Member
Joined: May 2001
Posts: 717
Lorton, Va USA
Redsy,
They had some of that stuff out in the early 50's, all the way to mid to late 60's. Still old rolls around when I came in the trade.

Cover NM with a cover and call it 90 deg?
What about the conductors inside? I don't think Dave Shapiro recommended that, but since he'll probably read this today, ring in on it Dave.

Next question, since the mid 70's you could use 60 deg C at a ballast, what fixtures now require 90? Is this a residential thing? I am in unfamiliar territory there.


#6931 - 01/16/02 08:04 AM Re: Old NM cable, stranded ground.  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Yes, it was David. I contacted the manufacturer, and they agreed that this was an acceptable fix. I'm not sure of the listing as far as application goes. But, in a pinch, it seems like a reasonable, if not ideal, solution. The material is available through McMaster Carr supply.

George, most, if not all new surface mount ceiling fixtures now require supply conductors rated 90C. This is a problem in houses wired prior to about 1985-86, when NM cable had 60C rated conductors. Since then NM cable has a 90C rating. The "B" in NM-B indicates the increased temp. rating.
BTW George, does David Shapiro really participate in, or at least scan this forum?

[This message has been edited by Redsy (edited 01-16-2002).]


#6932 - 01/16/02 10:22 AM Re: Old NM cable, stranded ground.  
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
A poster on another forum stated that sleeving the wire actually makes the problem worse for incandescent fixtures. The heat is mostly transferred along the conductor by conduction, not radiation or convection. The heat is transferred from the lamp base, to the fixture wires, and then to the branch circuit wires. Sleeving over the branch circuit wires would trap the heat in the conductor and make it travel farther down the conductor.
Don(resqcapt19)


Don(resqcapt19)

#6933 - 01/16/02 10:46 AM Re: Old NM cable, stranded ground.  
George Corron  Offline
Member
Joined: May 2001
Posts: 717
Lorton, Va USA
Redsy, yup, he does/did.
Don, that's what I was thinking when I saw it, sometimes I'm lucky in the things I don't have to inspect or deal with.
Yep, I well remember regular romex, and the associated problems, like you couldn't put it near a ballast


#6934 - 01/16/02 10:52 AM Re: Old NM cable, stranded ground.  
Elzappr  Offline
Member
Joined: Dec 2001
Posts: 270
Oregon
On the subject of 'sleeving cables' or 'sleeving wires', I think it would be ok in situations in which you are attempting to repair wiring that had been already cooked by too much heat, typically in fixture outlets. In the situation where one is in a continuous ambient heat situation, like in a fixture, or hot portion of an attic, high temperature sleeving will result in the conductor running hotter and transferring the heat to the unsleeved area of the wiring.. which wouldn't be any different than any other higher temperature rated wire. So, with this in mind, it makes sense to me that if you are going to sleeve some wire, make sure you do it out into the cooler ambient area, so the heat can safely dissipate. This would be practicable in some fluorescent fixture where you can get to the individual conductors, I suppose, but it would be cheaper to just replace the wire! Sleeving the cable makes no sense because the individual wires' insulation wouldn't hold up and eventually would carbonize and fault to ground or short out inside the jacket..this is the problem that Don alluded to. Redsy, just what context was the manufacturer referring to when stating that sleeving could be a fix?


#6935 - 01/16/02 12:55 PM Re: Old NM cable, stranded ground.  
Redsy  Offline
Member
Joined: Mar 2001
Posts: 2,056
Bucks County PA
I thought that the brittleness of the insulation was due to overlamping and therefore radiated from the fixture into the outlet box. I wouldn't think that enough additional heat beyond the rating of the lamp socket could be generated in the conductor by the additional current flow (1.7 amps v. 1 amp) caused by installing 2 100 watt lamps in a 60 watt max fixture.
Elzappr, they weren't necessarily endorsing this particular fix. I should have chosen my words more carefully, but they did say something that indicated this would be an acceptable solution to this problem. Of course, I don't know exactly who I spoke to. But McMaster Carr catalog states that this sleeving acts as a secondary insulator and provides increased temperature and abrasion resistance.


[This message has been edited by Redsy (edited 01-16-2002).]


#6936 - 01/16/02 02:49 PM Re: Old NM cable, stranded ground.  
Elzappr  Offline
Member
Joined: Dec 2001
Posts: 270
Oregon
Yeah, over-lamping is a big problem. The typical situation I have run into is a kitchen ceiling light that is hanging by its ground wire out of the ceiling outlet box, with all the insulation charred off the black and white wires, the box is heat damaged so the screws don't hold, and its a two story house! So, to prevent a major mess, if the copper wires aren't too discolored, or embrittled, I have resorted to using insulation stripped off other wires..better than tape.. to replace the bad insulation. I have found that the charring of the conductor insulation, and the browning of the NM jacket will only go to the staple. At that point it gets heat sinked enough to prevent further damage. (So, I get a little ticked off at those who are loose staplers!)


#6937 - 01/16/02 04:36 PM Re: Old NM cable, stranded ground.  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,306
Elzappr....

heat sink staples !?

that's a gem!

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