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#721987 - 07/17/12 03:48 PM wire size to 100 amp sub panel
Nikm Offline
enthusiast

Registered: 07/03/04
Posts: 201
Loc: L.A area Cali
Installing a new 200 amp panel and a 100 amp subpanel in attached garage. The wire run is going through the attic and is about 100 feet away. What size wire is needed for this run? thanks

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#721995 - 07/17/12 05:51 PM Re: wire size to 100 amp sub panel [Re: Nikm]
Able_Dog Offline
Carpal Tunnel

Registered: 12/07/03
Posts: 34877
Loc: N Georgia
I believe I used 2-2-2-4 for 100 amp at 100 ft several months ago, but wait for one of the electricians to confirm that.

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#722010 - 07/17/12 11:32 PM Re: wire size to 100 amp sub panel [Re: Able_Dog]
Nikm Offline
enthusiast

Registered: 07/03/04
Posts: 201
Loc: L.A area Cali
Well I know when the run was going to be 75 feet 3 was supposedly good for it. but its now going to be about 100' the one electrician was talking about running 3 still and I am not comfortable with that if it is in the gray area. Is the '4' you included for the ground wire size?

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#722139 - 07/18/12 10:34 PM Re: wire size to 100 amp sub panel [Re: Nikm]
MCA Offline
Carpal Tunnel

Registered: 03/09/06
Posts: 4943
Loc: Illinois
#2 is a good choice. #3 will probably be ok, voltage drop may or may not be an issue depending on the actual load.
2-2-2-4 means three #2's and one #4.

Since your going through an attic you may need to derate the ampacity based on ambient temperature. The 90 deg. ampacity for #3 copper is 110 amps, for ambient temp. over 105 deg. F derate by .87, if over 114 deg. F derate ampacity by .82 which will come to 90.2 amps. #3 may still be code compliant since the breaker size can be rounded to the next available breaker size.

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