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Need Circuit Breaker size for 4/3 Romex cable please
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Dennis
Dec 3, 2000, 12:00:40 AM12/3/00
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I am running 4/3 Romex with ground from an existing 200 Amp main service
panel and am running 40 feet to a new subpanel. The Romex is 4 gauge with 3
insulated conductors and a bare ground. Here's my need: The guy at Home
Depot told me to put a dual pole 100 Amp breaker in the existing main
service panel for this new wire, but I have a book that says 4 gauge wire is
rated as low as 70 amps and as high as 95 amps depending on the type of
jacket. The book talks about THHN jackets and other types. The 4/3 Romex
that I bought doesn't have any markings about the type of jackets used on
the conductors. Does anyone know for absolutely sure what this cable is
rated for? I will use a 70 amp breaker if needed, but would prefer to use
one higher rated if it's safe to do so.
panel and am running 40 feet to a new subpanel. The Romex is 4 gauge with 3
insulated conductors and a bare ground. Here's my need: The guy at Home
Depot told me to put a dual pole 100 Amp breaker in the existing main
service panel for this new wire, but I have a book that says 4 gauge wire is
rated as low as 70 amps and as high as 95 amps depending on the type of
jacket. The book talks about THHN jackets and other types. The 4/3 Romex
that I bought doesn't have any markings about the type of jackets used on
the conductors. Does anyone know for absolutely sure what this cable is
rated for? I will use a 70 amp breaker if needed, but would prefer to use
one higher rated if it's safe to do so.
Thanks!
Dennis
jjo...@my-deja.com
Dec 4, 2000, 8:20:31 PM12/4/00
to
The THHN insulation is rated for 90 Degrees C, however with NM cable
you must derate to 60 Degrees C. According to NEC the maximum allowable
ampacity of #4 copper wire is 70 Amps. In any case even at 90 Degrees C
the #4 is only good for 95 A Max. Go with the 70 A breaker and follow
Code. Your local building inspector should be able to help you before
you run in to any code violations with the work you are doing.
you must derate to 60 Degrees C. According to NEC the maximum allowable
ampacity of #4 copper wire is 70 Amps. In any case even at 90 Degrees C
the #4 is only good for 95 A Max. Go with the 70 A breaker and follow
Code. Your local building inspector should be able to help you before
you run in to any code violations with the work you are doing.
In article <YrkW5.30067$I5.5...@news1.rdc1.sdca.home.com>,
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Before you buy.
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