60 amp sub panel

[rickl]

i'm bidding on a 36 x 36 pole building 6-8' florescent t8 12 recp. my question is there a calculation formula for outbuidings, i'm running #4 al to a 60 amp main breaker sub panel i'm thinking maybe 20 25 total load. The thing that got me thinking was at home depot i read a sign that said #4 thhn al and #6 thhn cu is good for only 50 amp. theres nothing wrong with feeding a 60 amp panel with #4 thhw al or #6 thhw cu is there. correct me if i'm wrong but don't you size the feeder on the calculated load, then you can upsize to the next size breaker

 

[bob]

Re: 60 amp sub panel

Ricky
Use the 75C rating of 65 amps for #4 AL. I think #6 cu is rated 65 amps. Ther are no tables for your building.

 

[ron]

Re: 60 amp sub panel

Bob,
How do you know the terminations are rated for 75 deg? The NEC says to use 60 deg values if you don't know the termination temps and you are less than 100A.

 

[jimwalker]

Re: 60 amp sub panel

Unless the specs call for 60 amps i would just run 10-3/wg U F cable.Possibly only 12-3 .Are they seeking quality or just price ?

 

[rickl]

Re: 60 amp sub panel

ron
lets say there 60c terminations #4 al is good for 55. so if i say the calculated feeder load is 51 amps then i legal could put then on a 60 amp breaker(next size up breaker rule)???
jim
if i ran 10-3 wg i could only put a 30 amp service with 4 120 v circuits in the building (230.79-b)which only leaves 1 120 volt circuit for the future.

 

[jimwalker]

Re: 60 amp sub panel

Is this commercial use or on private property behind a house ?

 

[rickl]

Re: 60 amp sub panel

private property behind a house.

 

[jimwalker]

Re: 60 amp sub panel

So all i see required is 1 circuit for receptacles and 1 for the lights

 

[caosesvida]

Re: 60 amp sub panel

keep in mind line loss, if you are running a long distance. Also it seems like if you run a larger system to the pole barn, the owner will appreciate it in the long run.

 

[steve66]

Re: 60 amp sub panel

posted by rickl:

lets say there 60c terminations #4 al is good for 55. so if i say the calculated feeder load is 51 amps then i legal could put then on a 60 amp breaker(next size up breaker rule)???

Yes, that is correct.

Posted by ron:

How do you know the terminations are rated for 75 deg?

Square D notes the following on their type QO breakers:

10-30 A circuit breakers are suitable for use with 60 deg C or 75 deg C condutors. 35-125 A circuit breakers are suitable for use with 75 deg C conductors.

I assume this means you can use the 75 deg wire ratings if you have these breakers on both terminations.

Steve