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#205504 - 02/27/12 08:02 PM Old 500 mcm cable
SJT Offline
Member

Registered: 07/24/02
Posts: 242
Loc: PATCHOGUE, N.Y.
There is an old (1960's) unfused 600 amp disconnect fed with parrallel 500's.
We are looking to replace the switch. I was wondering what type of insulation was used back then. I should send a picture of the wire.
For an amperage rating of these wires, can I use the left coloumb (310.15(B)(16) in the NEC (60c-TW), to play it safe?
I know that table will give it a lower rating, plus I have to derate 70%. It's 6" gal, with 6-500's, and 2-250's for the nuetral.
Thanks, SJT

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#205508 - 02/27/12 10:41 PM Re: Old 500 mcm cable [Re: SJT]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
TW is a good guess.
_________________________
Greg Fretwell

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#205511 - 02/28/12 07:33 AM Re: Old 500 mcm cable [Re: SJT]
EV607797 Offline
Member

Registered: 10/25/06
Posts: 756
Loc: Fredericksburg, VA, USA
Most of the larger sizes that I ever saw from that era were either THW or RHHW. I don't remember seeing type TW in anything above #10, but I'm not saying that it didn't exist.
_________________________
---Ed---

"But the guy at Home Depot said it would work."

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#205515 - 02/28/12 09:25 AM Re: Old 500 mcm cable [Re: SJT]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
I guess I was really just trying to establish a column in 310.16
I agree the insulation did not look like TW. I used to have a piece of 750 MCM under the seat of my car as a persuader in serious social situations.
_________________________
Greg Fretwell

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#205521 - 02/28/12 05:35 PM Re: Old 500 mcm cable [Re: SJT]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6804
Loc: Brick, NJ USA
I still have a piece of 600THHN for the persuader; hopefully it will just stay where it is.

I remember an industrial demo job that had 500 RHHW, and some 'newer' THW. Both had the same values at the scrap yard!!
_________________________
John

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#205523 - 02/28/12 09:08 PM Re: Old 500 mcm cable [Re: SJT]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
I don't know where that piece of 750 is now. I gave it to my old buddy who was a cable splicer for Ma Bell. He planned on stripping it, dipping the fluxed strands in a lead pot and making a big lead head mace like you make a candle.
_________________________
Greg Fretwell

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#205525 - 02/28/12 11:08 PM Re: Old 500 mcm cable [Re: SJT]
NORCAL Offline
Member

Registered: 09/25/02
Posts: 807
There is a building locally, that has 350 MCM TW (260A) for the main w/ 400A fuses in the main switch, the load regularly exceeded the rating of those conductors in the summer.

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