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Monday, April 25, 2016
Question:
Good morning and thanks for the insight you give us all.
If running underground service conductors from the power company hand hole to the meter 230.31 (A) states underground service conductors shall have sufficient ampacity to carry the current for the load as calculated in accordance with Article 220 and shall have adequate mechanical strength. I need to replace existing conductors that have been damaged. The load is a 5 amp battery charger for gate motors and 2-lights at 120 watts each. The installation is a residential gate service.
The main breaker is 150 amp 120/240V single phase. I believe 230.31(A) would allow me to run conductors as small as #8 cu per 230.31 (B). My local plans examiner and code guru says the wires would be over fused and I need to run conductors rated for 150 amps even though the over current protection is talking about is after the service conductors.
Thanks for your consideration. Tom Towner
A
Answer:
Hey Tom thanks for your question and the kind words. You are correct that 8 AWG copper is permitted as stated in 230.31(B). But 230.90(A) in general requires the overcurrent protection to not exceed the conductor's allowable ampacity. Either you can replace the 150 ampere circuit breaker with something smaller or install conductors that would be protected by the 150 ampere circuit breaker. You are correct that the overcurrent protection is at the load end of the service conductors so it is overload protection as stated in 230.90.