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#63824 - 03/25/06 08:15 PM Updating Wire Temp.
BigJohn Offline
Registered: 03/06/04
Posts: 391
Loc: Boston, MA
When dealing with old 60 degree rated wiring, is it considered an acceptable fix to heat-shrink it for use with fixtures requiring 90 degree wiring?

I can get heat shrink with a minimum activation temperature of 125 degrees C. and a 600V insulation rating. It seems to me that this would be sufficient for protecting conductors in a 90 degree enviroment.


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#63825 - 03/26/06 11:03 AM Re: Updating Wire Temp.
macmikeman Offline
Registered: 07/16/02
Posts: 717
Loc: Honolulu, Hawaii
I can give you an opinion John. What you are thinking about should be more than sufficient. But a lawyer in a courtroom would be able to shred it apart. So you won't be likely to find an approval from an AHJ for the method.
#63826 - 03/26/06 11:04 AM Re: Updating Wire Temp.
renosteinke Offline
Cat Servant
Registered: 01/22/05
Posts: 5316
Loc: Blue Collar Country
I can't give you an "official' answer, but....

Heat shrink is a wonderful thing. I've used it many times to restore insulation that was "cooked" by the light having too bright a bulb in it. I've used it to replace other damaged insulatio, as well.

I've installed fixtures that called for hi-temp wire in the past; my preferred solution is to have another junction box nearby, well away from the heat, and transition there to a higher-temp wire.

I assume that you're dealing with existing wiring. I would be willing to try using heat-shrink tubing; I'd also want to have the stuff extend well into the conduit, beyond where I can 'shrink' it.
#63827 - 03/26/06 11:48 AM Re: Updating Wire Temp.
Redsy Offline
Registered: 03/28/01
Posts: 2056
Loc: Bucks County PA

Search for "wire sleeving".
In a pinch, I have used the sleeving on page 737. Slide it over the old insulation and it increases the temp. rating accordingly.

[This message has been edited by Redsy (edited 03-26-2006).]
#63828 - 03/26/06 11:48 AM Re: Updating Wire Temp.
Dave T Offline
Registered: 01/22/05
Posts: 155
Loc: Waukesha, WI, USA
I've used heat shrink but someone brought up a very important point on one of the other fprums a while back.
Most of us focus on the fact that the ambient heat from the fixure is what we're trying to deal with but forget that the copper is not only a good conductor of electricity but also heat. As such one should not ignore the fact that heat is being conducted by the copper potentially beyond the box itself. So what about the insulation just outside the box?
I realize that this may or maynot be a problem and some might consider it to be spitting hares but can it be confirmed that the insulation temperature wouldn't be exceeded outside the box itself?
And, yes, I do carry heat shrink tubing in my took box with a heat gun. But are we making an informed decission when we repair or reinsulate the wires?
This is something that I never thought of at first.
#63829 - 03/26/06 11:55 AM Re: Updating Wire Temp.
iwire Offline
Registered: 01/05/03
Posts: 4391
Loc: North Attleboro, MA USA
I am with you Dave.

Much of the heat a conductor at a lighting outlet is exposed to is the heat the travels from the filament along the filament legs through the socket and into the field wiring.

Those of you that service HID fixtures will be familiar with the fact that the porcelain sockets are often fasted to a large piece of aluminum which works as a heat sink to draw much of the heat off the socket and into the fixtures enclosure.
Bob Badger
Construction & Maintenance Electrician
#63830 - 03/26/06 12:02 PM Re: Updating Wire Temp.
JoeTestingEngr Offline
Registered: 11/04/05
Posts: 781
Loc: Chicago, Il.
I'm not too comfortable thinking that the heat might transfer through my hi-temp heat shrink and melt any insulation that it was shrunk down onto. I like Reno's preferred solution.
#63831 - 03/26/06 12:30 PM Re: Updating Wire Temp.
sierra electrician Offline
Registered: 02/12/05
Posts: 219
Loc: North Fork, CA USA
Heat Shrink is a cool idea but, by the time the coating on the wire is cooked, the copper is usually weakend to an unusable state and needs to be replaced.
I would not reccomend this. If the wire cannot be trimed back to a point where you get good copper & coating....forget it. Replace it!


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