Tradesmanx
Member
- Location
- Sammamish, WA
According to NEC 690.9 (B): Overcurrent Devices in pv system DC circuits...shall be rated with one of the following: "not less than 125% of the maximum currents calculated in 690.8(A)..."
However, this relates to DC circuits. The Inverter output is AC since the DC circuit has already been converted to AC electricity. I can't find anything to suggest the circuit breaker needs to be 125% of the inverter output rating. In this case, the Solar Edge 10000 single phase residential inverter has a continuous output rating of 42 amps. If the backfed breaker was required to be 125%, we would put in a 60amp breaker. We used 6 AWG THHN wire rated at 65 or more amps, so no problem there. But, why would you protect 42 amps with a 60 amp breaker? This makes no sense. Yet, there does seem to be an industry standard to size the breaker at 125%. But, I can't find that in the 2017 code. In fact, the code says no overcurrent protection is required at all...as I read it. For instance, a line side tap has no overcurrent protection. No breaker. I would like to use a 50 amp breaker and call it good.
What I read in the code says, "690.8(A)(3) The maximum current shall be the inverter continuous output current rating." Am I missing something? If so, what? Where does the code direct inverter output overcurrent circuit breakers to be 125% of the inverter continuous current rating?
However, this relates to DC circuits. The Inverter output is AC since the DC circuit has already been converted to AC electricity. I can't find anything to suggest the circuit breaker needs to be 125% of the inverter output rating. In this case, the Solar Edge 10000 single phase residential inverter has a continuous output rating of 42 amps. If the backfed breaker was required to be 125%, we would put in a 60amp breaker. We used 6 AWG THHN wire rated at 65 or more amps, so no problem there. But, why would you protect 42 amps with a 60 amp breaker? This makes no sense. Yet, there does seem to be an industry standard to size the breaker at 125%. But, I can't find that in the 2017 code. In fact, the code says no overcurrent protection is required at all...as I read it. For instance, a line side tap has no overcurrent protection. No breaker. I would like to use a 50 amp breaker and call it good.
What I read in the code says, "690.8(A)(3) The maximum current shall be the inverter continuous output current rating." Am I missing something? If so, what? Where does the code direct inverter output overcurrent circuit breakers to be 125% of the inverter continuous current rating?