100 amp sub panel

[irelandnewyork]

Hi Guys,
Can a 100 amp sub panel be fed from a 100 amp breaker in a main panel, with # 4 size cable rated at 95 amps is there an exception for this.
Thanks for the replys

 

[Little Bill]

Hi Guys,
Can a 100 amp sub panel be fed from a 100 amp breaker in a main panel, with # 4 size cable rated at 95 amps is there an exception for this.
Thanks for the replys

No exception that I know of unless it is for some type of motor circuit or HVAC, or other things in 240.4(G). The 95A rating is under the 90 deg. column and that is usually only for derating purposes.

 

[suemarkp]

No, because there is no 75C #4 wire rated above 85A for this application. You can't use the 90C temp rating because the breaker and lug terminations are limited to 75C.

You can use #4 only if the calculated load is 85A or less in which you can round up to a 90A breaker. Things get worse with SE cable or other types which are limited to 60C.

 

[ActionDave]

Nope. 90C table won't for you here.

 

[irelandnewyork]

100 amp sub

100 amp sub

To make things more complicated ill give an idea of the whole story.
From a 200 amp disconnect (A) i have 3/0 feeding a main panel (B), here they are landed in a 3p 100 amp breaker halfway down the panel that feeds this panel ( no main lug kit or main breaker so to speak on this panel ). From this panel the client wants to install a 3p 100 amp lighting panel, (C).
Am i wrong in thinking i could put a main lug kit on panel (B) put the 3/0 in here and use the 100 amp breaker with new # 4 installed to the new 100 amp sub lighting panel.
From what im getting i think i would have to up the sub panel feeders to # 3 to protect them at 100 amps,
i was tryin to keep the pipe size at 1", if i use # 3 i will have to go to 1.25 pipe.
Hope this makes sense and thanks for reading and replying

C

 

[ActionDave]

If the panel is 200A rated, nothing wrong with adding a main lug kit. Still need to use a 90A breaker for the 4AWG. 90A would be enough most days of the week.