TorC
Solar Enthusiast
- Joined
- Jan 13, 2022
- Messages
- 514
Bit of a knotty one here. I'm more interested in electrical correctness than NEC compliance or similar in this case. Setting up an off-grid system in a place where grid exists, and is planned to be used solely as the first generator backup.
Utility side, comes into N-G bonded main panel, and the outbuilding on which the PV system is installed is has a 30A breaker with 10/3+G running to it. That is planned to be run to the inverter generator/grid input. Old buried cable is not changing in the foreseeable future.
PV side, 12kW of 120/240V inverter, 50A total continuous output, neutral/ground isolated in inverter, runs to a main service panel with only combined neutral/ground busbars, as yet unwired.
As I look at it, the issues/questions are thus:
1: 10ga ground feed is inadequate for 50A+ in the shop panel, and therefore a ground rod is needed for the shop. NEC says the same, so ground rod being electrically desirable here or not is a moot point: install the ground rod.
2: In full off-grid I need a a neutral ground bond, which should be in the shop panel. In this mode, combining neutral and ground to the busbars is correct, however:
2a: If the inverter is drawing from the grid to make up power for any reason, it is improper for the neutral and ground to be on the same busbars at the shop.
2b: Even so, 50A of inverter service in the shop is more than should be relying on a single N-G bond back an the utility service entrance panel across 10ga N&G.
3: If I bypass the inverters and take care about how much power I draw, I must not have N-G bonded in the shop panel, and need to figure out how to isolate these in a panel not designed for such use.
According to the manual, the Outback Radian inverters I have are designed with all neutrals common. No word I can find on whether I can connect only the 240V L1/L2 to have two isolated N-G bonds.
Thoughts from those who have more experience with this kind of thing on what you might do in a situation similar to mine would be much appreciated.
Utility side, comes into N-G bonded main panel, and the outbuilding on which the PV system is installed is has a 30A breaker with 10/3+G running to it. That is planned to be run to the inverter generator/grid input. Old buried cable is not changing in the foreseeable future.
PV side, 12kW of 120/240V inverter, 50A total continuous output, neutral/ground isolated in inverter, runs to a main service panel with only combined neutral/ground busbars, as yet unwired.
As I look at it, the issues/questions are thus:
1: 10ga ground feed is inadequate for 50A+ in the shop panel, and therefore a ground rod is needed for the shop. NEC says the same, so ground rod being electrically desirable here or not is a moot point: install the ground rod.
2: In full off-grid I need a a neutral ground bond, which should be in the shop panel. In this mode, combining neutral and ground to the busbars is correct, however:
2a: If the inverter is drawing from the grid to make up power for any reason, it is improper for the neutral and ground to be on the same busbars at the shop.
2b: Even so, 50A of inverter service in the shop is more than should be relying on a single N-G bond back an the utility service entrance panel across 10ga N&G.
3: If I bypass the inverters and take care about how much power I draw, I must not have N-G bonded in the shop panel, and need to figure out how to isolate these in a panel not designed for such use.
According to the manual, the Outback Radian inverters I have are designed with all neutrals common. No word I can find on whether I can connect only the 240V L1/L2 to have two isolated N-G bonds.
Thoughts from those who have more experience with this kind of thing on what you might do in a situation similar to mine would be much appreciated.
