I'm working on a project that we will be using approx. 40KW DC power to produce approx. 50KWH/per year. The building voltage is 480/277V with 1200A service. The PV system we are proposing to use will have mutiple (4) clustor of PV panels with 4- 10KW inverters. The thought is, each inverter is to feed a sub-panel (4-lighting panels). I was told I can not feed sub-panels from PV system, it has to go to the main switchboard. Is this true that I can not feed sub-panels from PV system? Thanks,
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PV for Sub-Panel
- Thread starter faresos
- Start date
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- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Per the NEC and assuming that there are no local amendments to confuse things, you can feed your PV Grid Tied Inverter (GTI) outputs into a sub panel.I'm working on a project that we will be using approx. 40KW DC power to produce approx. 50KWH/per year. The building voltage is 480/277V with 1200A service. The PV system we are proposing to use will have mutiple (4) clustor of PV panels with 4- 10KW inverters. The thought is, each inverter is to feed a sub-panel (4-lighting panels). I was told I can not feed sub-panels from PV system, it has to go to the main switchboard. Is this true that I can not feed sub-panels from PV system? Thanks,
One of the restrictions though is that the 120% rule for the loading on the sub-panel bus as well as the 120% rule for the sub-panel's connection at the main panel must be met.
Another is that the entire sub-panel's breaker at the main panel may need to be labelled as the AC disconnect for the PV system, since the only place for a disconnect for the PV feed only could be located is between the GTI and the sub-panel. You may be able to comply with disconnect requirements by putting a contactor at the sub-panel with control from the main panel location.
If you are, as it appears, looking at connecting each GTI to a different sub-panel, the above restrictions get more complicated.
Since your proposed installation's wattage is above the commercial threshold in most states, the utility may have additional rules that you must satisfy even though the wiring will be on your side of the service point.
BillK-AZ
Senior Member
- Location
- Mesa Arizona
You could have major problems, things to check out include:
The SES likely has GFP (Art. 215.10 & 230.95 may apply). If there is a main breaker or fused switch with GFP, you have to make sure it is suitable for back feed. Then comes the real problem in many cases, you have to have coordinated GFP on the feeder breakers and I have yet to find a suitable GFP breaker that is not marked line/load. This is due to the way most (if not all) GFP works. You need to get with real technical help from the SES manufacturer.
An alternative is line side connection (NEC 705.12(A)), but this is not compatible with your desire to feed existing panels. It is often difficult to do within an SES as the SES manufacturers often just say NO.
Another possible problem is utility policy; many utilities require that there be a single PV production KWH meter and AC disconnect and this is incompatible with using multiple panels for connection. Ask the utility about their policy on this.
The SES likely has GFP (Art. 215.10 & 230.95 may apply). If there is a main breaker or fused switch with GFP, you have to make sure it is suitable for back feed. Then comes the real problem in many cases, you have to have coordinated GFP on the feeder breakers and I have yet to find a suitable GFP breaker that is not marked line/load. This is due to the way most (if not all) GFP works. You need to get with real technical help from the SES manufacturer.
An alternative is line side connection (NEC 705.12(A)), but this is not compatible with your desire to feed existing panels. It is often difficult to do within an SES as the SES manufacturers often just say NO.
Another possible problem is utility policy; many utilities require that there be a single PV production KWH meter and AC disconnect and this is incompatible with using multiple panels for connection. Ask the utility about their policy on this.
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