8 300kcmil Close enough?

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480sparky

Senior Member
Location
Iowegia
More info, please:

Resi or commercial? Service, or feeder/branch? Copper or aluminum? What type of insulation? Any derating needed?

My first reaction is it's way too big. 300 copper is 240-320amps in T310.16.
 

iwire

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Location
Massachusetts
natfuelbill said:
400A Main service breaker, copper, using the 75C THWN

THWN only? Not dual rated THHN?

OK,

300 CU @ 75 C = 285 amps

285 x 2 = 570 amps

Six current carrying condutors get reduced to 80%

570 x .8 = 456 amps
 

infinity

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Location
New Jersey
Occupation
Journeyman Electrician
natfuelbill said:
The N will have the unbalanced and non-linear.

399 is not 400 .........


"Major portion" equals more than 50% nonlinear. And 399 is close enough if the connected load is 399 or less.
 

iwire

Moderator
Staff member
Location
Massachusetts
natfuelbill said:
The N will have the unbalanced and non-linear.

399 is not 400 .........

For a guy that is asking for help your making this hard.

Did you read the section I pointed out?

Is the major portion of the load non-linear?

And I asked for the calculated load back at the start for the same reason Dennis and Trevor mentioned it.

240.4(B) may help you out based on the load not the breaker.
 
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