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garydbarger
sub panel cable rating

I have a 125 amp sub panel box in a cabin. I will be feeding it from a 200 amp main box in a house using a 100 amp plug in breakers to feed the sub panel. I have found some #2 copper cable with markings as #4 awg MTW or THHN, or THWN. It will be ran in 2" PVC conduit in ground. Will this cable be heavy enough on 100 amp breakers at max load. Thanks Gary

Lyle
Re: sub panel cable rating

#2 thhn Cu is rated for 125 amps, because you only need to worry about the wire matching the ampacity of the breaker you could
get by with #3 thhn Cu for the 2 hot conductors & the neutral, but chances are that home improvement stores don't carry #3. #8 thhn Cu is the minimum equipment grounding conductor you can use
for a 100 amp circuit. 2" pvc is over kill, but I am all for it,
because in the future you may need to pull larger or more conductors in this pipe.

I have based my recommendations on the NEC, your State or local inspectors might have more strigent codes. You could talk your local electrical inspector to come out & give you ideas about what is required for your installation. You may not like what he has to say, but keep in mind codes protect you, your family and the next family to own your home.

Ernie_Fergler
Re: sub panel cable rating
Lyle wrote:

#2 thhn Cu is rated for 125 amps, because you only need to worry about the wire matching the ampacity of the breaker you could
get by with #3 thhn Cu for the 2 hot conductors & the neutral, but chances are that home improvement stores don't carry #3. #8 thhn Cu is the minimum equipment grounding conductor you can use
for a 100 amp circuit. 2" pvc is over kill, but I am all for it,
because in the future you may need to pull larger or more conductors in this pipe.

I have based my recommendations on the NEC, your State or local inspectors might have more strigent codes. You could talk your local electrical inspector to come out & give you ideas about what is required for your installation. You may not like what he has to say, but keep in mind codes protect you, your family and the next family to own your home.

Sound advice indeed, but in these parts all inspectors would rather see 2&1/2" PVC....

Dave357
Re: sub panel cable rating
garydbarger wrote:

I have found some #2 copper cable with markings as #4 awg MTW or THHN, or THWN.

If it's marked #4 AWG, then it's #4 AWG, NOT "#2 copper cable".

What leads you to believe that it's #2?

garydbarger
Re: sub panel cable rating

my mistake, it is # 4 copper, I was thinking #2 but it is for sure #4

jwhite480
Re: sub panel cable rating

Number 4 is fine on a 100 amp breaker for this feeder. Number 8 ground is needed, and number six for the grounding electrode conductors.

djohns
Re: sub panel cable rating

Welcome back jwhite . :D

Re: sub panel cable rating

Good call Guys. Just remember some areas of the country require this to be considered a new service. Even thoughit is feed from a main panel and feed to a out building. That requires you to bond the nuetral bar to the panel can. and new driven ground.

goldhiller
Re: sub panel cable rating

Didn't see any mention of distance. Voltage drop could be a concern, not?

http://www.csgnetwork.com/voltagedropcalc.html

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