Sizing the breaker feeding a whole house.

[Jerry@Id]

When sizing the main breaker feeding a whole house using the standard method of calculation for a single family dwelling for the 2023 NEC. 310.12 A & B says the conductors can be 83% if the feeder is rated 100 amps through 400 amps. Do you also reduce the breaker or does it need to stay at 100%? Example, after your calculation you come out with 175 amps, 175 X 83% = 145.25. Does the breaker need to be 150 amp or 175 amp?

 

[LarryFine]

Do you also reduce the breaker or does it need to stay at 100%? Example, after your calculation you come out with 175 amps, 175 X 83% = 145.25. Does the breaker need to be 150 amp or 175 amp?

Welcome to the forum.

It doesn't need to stay at 200a, it gets to stay at 200a.

 

[infinity]

Are these feeder or service conductors?

 

[Jerry@Id]

Breaker and conductors for the service.

 

[infinity]

Example, after your calculation you come out with 175 amps, 175 X 83% = 145.25. Does the breaker need to be 150 amp or 175 amp?

You could size the conductors to 83% of the service rating so if you had a 200 amp OCPD you would use that ampacity in the 83% calculation.

310.12(A) Services.
For a service rated 100 amperes through 400 amperes, the service conductors supplying the entire load associated with a one-family dwelling, or the service conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling, shall be permitted to have an ampacity not less than 83 percent of the service rating. If no adjustment or correction factors are required, Table
310.12 shall be permitted to be applied.

 

[Jerry@Id]

Thank you!

 

[Jerry@Id]

Can you explain in detail how you derate the neutral for both the standard and optional calculations.