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johnnyelectric369

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I am just double checking my math here and I can use some input. Can I use a #3 Copper THHN/THWN from the 75 degree column (100a) from a 60/75 degree rated 90 amp breaker terminating at a 75 degree rated 100 amp sub panel? or could I use #4 THHN/THWN2 from the 90 degree column (95a)? Does it come down to cost? I have been thinking about it all day. Thank you in advance for your help and responses!
 
Your conductor must be rated to carry the load and that would be your first consideration. You also must keep 11014(C) in mind and take your termination temperature into allowance with. 75° is the most common termination.
Your #4 THHN is rated 85 amps at 75° so using that the load would be limited to 85 amps and the largest breaker allowed would be 90 amp.
A 100 amp load would require a #3 on a 100 amp breaker

(all above assuming no deratings required)
 
augie47 said:
Your conductor must be rated to carry the load and that would be your first consideration. You also must keep 11014(C) in mind and take your termination temperature into allowance with. 75° is the most common termination.
Your #4 THHN is rated 85 amps at 75° so using that the load would be limited to 85 amps and the largest breaker allowed would be 90 amp.
A 100 amp load would require a #3 on a 100 amp breaker

(all above assuming no deratings required)
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This is just a replacement for an existing pool sub panel for a future pool. It is old aluminum wiring with no neutral so I am piping a new circuit to it with neutral. There is no load for the time being. So can I get away with pulling #4 since there is no load and leave it to the future electricians to keep the load within 80% of 90 amp breaker?
 
johnnyelectric369 said:
This is just a replacement for an existing pool sub panel for a future pool. It is old aluminum wiring with no neutral so I am piping a new circuit to it with neutral. There is no load for the time being. So can I get away with pulling #4 since there is no load and leave it to the future electricians to keep the load within 80% of 90 amp breaker?
Click to expand...
A 90a breaker will most likely be sufficient for a regular residential pool. Why not pipe and pull aluminum and use 1 or 2 awg aluminum. You can pull a copper EGC if you prefer too with the hots and nuetral being aluminum
 
letgomywago said:
A 90a breaker will most likely be sufficient for a regular residential pool. Why not pipe and pull aluminum and use 1 or 2 awg aluminum. You can pull a copper EGC if you prefer too with the hots and nuetral being aluminum
Click to expand...
I would love to but the customer loves copper. Don't even get me going on that battle. Lol. They have #2 aluminum in the panel going to the sub now with no neutral tho. Ill give them the peace of mind of good old copper. So a #3 would be good enough do you think or is it overkill and go with #4?
 
So you left out important information. Customer wants a premium install. In that case sell them 3awg copper. If they bawk at the price tell them that's what it costs. You don't want to argue in the end when they find out the panel is only good for 85a not 100a.
 
johnnyelectric369 said:
I would love to but the customer loves copper. Don't even get me going on that battle. Lol. They have #2 aluminum in the panel going to the sub now with no neutral tho. Ill give them the peace of mind of good old copper. So a #3 would be good enough do you think or is it overkill and go with #4?
Click to expand...
If they want you to use the copper use #3 and since the panel is 100 amps make the feeder circuit breaker 100 amps also. They'll get 10 additional amps for "free".
 
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