400 A service conductor size

[cppoly]

Why are 500 kcmil conductors allowed for 400 A? The terminals must be rated for 90 degrees C?

 

[augie47]

The 75? rating of 500 kcmil cu is 380 amps.
240.4(B) will allow you to go to the next higher overcurrent device in most cases.
Some inspectors might ask that you confirm the calculated load to be 380 amps or less.

 

[cppoly]

So the term 400 A service is defined by the OCPD and not the load amps.

 

[Dennis Alwon]

So the term 400 A service is defined by the OCPD and not the load amps.

It is commonly called a 400 amp service even though it is technically rated 380 amps. This could be a problem if the load was greater than 380 amps. Usually a very unlikely occurrence if it is a residential panel. I have one now that is calculated at 350 amps but I doubt it will see that very often or ever.

 

[mistermudd]

Only works for 800 amps or less, for larger than 800 amps the service conductors must be rated larger that the OCPD. Unless... it is a main lug only panel than the service conductors can be sized per the calculated load. You may be required to label the service equipment with the actual rating of the service conductors. I know.......TMI

 

[cppoly]

Thanks

 

[kwired]

common misapplication is when people assume 400 amps for 500Kcmil and try to parallel sets to get 1200, 1600, 2000 amps. As was said you can not use next higher overcurrent device for over 800 amps. 380 x 3 = 1140, can not be protected by a 1200 amp overcurrent device.

 

[infinity]

Another common misapplication is to use one set of 500's on a transformer secondary feeding a 400 amp OCPD. In that scenario you would need conductors rated for 400 amps or larger since the next size up rule doesn't apply.

 

[iwire]

So the term 400 A service is defined by the OCPD and not the load amps.

No, a service with a 400 amp OCPD supplied with 500 kcmil copper would be a 380 amp service.