Redi Electric
Member
My question relates to using SER for a service in a single-family dwelling. I just had an inspector tell me that I had to de-rate SER because, in Article 338, Section II, 338.10 (B) (4) (a), in interior installations for branch circuits and feeders, SER must comply with Part II of Article 334.
In Part II, Section 334.80 it states that Type NM and NMC must be rated in accordance with the 60-degree column of Table 310.16.
I believe this ignores the intention of Article 310.15 (B) (6) and the accompanying Table 310.15 (B) (6) which allows, in a single family residence, the use of 4/0 Aluminum SER for a 200 amp service. The inspector will not allow me to use Table 310.15 (B) (6) and wants me to use the 60 degree column of Table 310.16 which requires 300 mcm for 190 amps (this qualifies for 200 amps using the next size up rule).
I see no exception in Article 310.15 (B) (6) and Table 310.15 (B) (6) that requires the SER to be de-rated.
I can see the reasoning behind requiring the de-rating for a feeder or branch circuit that supplies a load that can be operated continuously such as a range or oven but it seems the whole purpose of Table 310.15 (B) (6) is to allow for a residential demand factor.
We have been using 4/0 Aluminum SER for 200 amp services and 42 circuit 200-amp main breaker panels for years but now the inspector wants us to replace the 4/0 or replace the meter main breaker with a 150-amp breaker but only if the assembly is UL approved.
Luckily, Cutler Hammer uses the same bus in its 150-amp and 200-amp meter mains but the 150-amp breaker is well over $100.
If SER has to be de-rated for a service then why is it even mentioned in 310.15 (b) (6)?
The whole issue is even stranger because the 4/0 SER only supplies one of two panels in the residence. There is another 100-amp panel that is fed directly from the 200 amp meter-main with a separate feeder, and the 4/0 SER is only carrying about 60% of the calculated load
Has anyone dealt with this issue?
In Part II, Section 334.80 it states that Type NM and NMC must be rated in accordance with the 60-degree column of Table 310.16.
I believe this ignores the intention of Article 310.15 (B) (6) and the accompanying Table 310.15 (B) (6) which allows, in a single family residence, the use of 4/0 Aluminum SER for a 200 amp service. The inspector will not allow me to use Table 310.15 (B) (6) and wants me to use the 60 degree column of Table 310.16 which requires 300 mcm for 190 amps (this qualifies for 200 amps using the next size up rule).
I see no exception in Article 310.15 (B) (6) and Table 310.15 (B) (6) that requires the SER to be de-rated.
I can see the reasoning behind requiring the de-rating for a feeder or branch circuit that supplies a load that can be operated continuously such as a range or oven but it seems the whole purpose of Table 310.15 (B) (6) is to allow for a residential demand factor.
We have been using 4/0 Aluminum SER for 200 amp services and 42 circuit 200-amp main breaker panels for years but now the inspector wants us to replace the 4/0 or replace the meter main breaker with a 150-amp breaker but only if the assembly is UL approved.
Luckily, Cutler Hammer uses the same bus in its 150-amp and 200-amp meter mains but the 150-amp breaker is well over $100.
If SER has to be de-rated for a service then why is it even mentioned in 310.15 (b) (6)?
The whole issue is even stranger because the 4/0 SER only supplies one of two panels in the residence. There is another 100-amp panel that is fed directly from the 200 amp meter-main with a separate feeder, and the 4/0 SER is only carrying about 60% of the calculated load
Has anyone dealt with this issue?
