400 amp panel conductor size (not a service)

[journeyman0217]

I was reading some past threads and I'm still not clear on how to size wire for a 400 amp sub panel. 500 kcmil is good for 380amps at 75 degrees. Can I use the next standard size breaker, in this case 400 amp, to protect these conductors as long as the connected load is less than 380 amps? And if the connected load is greater than 380 amps does the next size up rule still apply?

 

[augie47]

215.2 requires the feeder ampaciy must be equal or greater than the load served. Once you have met that requirement, the 240.4 next size up rule can be applied.

 

[journeyman0217]

Ah thank you. So if I'm feeding a panel where the current connected load is less than 380 amps then 500's would suffice. That throws me off though because if someone looks at a 400 amp panel they may assume it's good for 400 amps but in reality its only good for 380 due to the conductor size.

 

[augie47]

In reality that 20 amps would not be of much consequence but your point is certainly valid is situations with greater numbers and, especially where you have multiple service disconnects fed by one set of service conductors. It's why we stress the need for knowledgeable personnel on jobs.