kumasan
Member
- Location
- Northern California
- Occupation
- Electrical Engineer
Hello, Im in the process of upgrading a microinverter based solar system and I would appreciate help to review my plans and the applicable codes.
I will be surpassing the limits I can backfeed into the main panel. My load calc is around 100A max so the 200A service is fine, I just need to work around the busbar issue. I am thinking to install a 400a generation panel to take care of the extra solar backfeed. My setup would be:
200A Combo Main panel with feedthrough lugs feeding backfed 200A breaker in a 400A generation panel. No other loads in the main combo meter/panel Per NEC sum of breakers rule 705.12(d)(2)(3)(c).
Solar AC combiner panel with 200A Main breaker feeding the main lugs of the 400A panel at the opposite end of the Generation panel.
Ill be at a little under 100A of backfeed solar, but I am thinking to go with a 200A breaker for future expansion(see question below).
My main house distribution 200A subpanel will be fed by a 200A breaker from the middle of the 400a generation panel.
My question is related to the grounding needs for the system. I currently have sufficient grounding for 200A (2 rods and #4 to them for protection under the older codes), pvc water supply so no bonding, no ties to rebar/concrete.
Im having a challenge interpreting the NEC 250.66 requirements to see if my current 200A grounding is sufficient or I need to upgrade things anywhere in the system.
According to 250.66 which seems to be written from the perspective of a single supply source at the service entrance. It seems that since my service remains at 200A then I should be ok with my current grounding for the GEC based on the 200A service. Actually with only rods it seems #6 would be sufficient as 250.66(a) says the grounding electrode to the rods needs to be #6 max? Even if I did have a 400A service its not clear that I would have to change anything since Im ground rod based?
About the codes, I am uncertain about is that once I start backfeeding solar with multiple sources the theoretical max current goes above the 200A. Most of the wording of the code refers to parallel connections in terms of two parallel conductors to form a larger effective conductor which is much different than mutli source that happens with solar backfeed. I was not able to find any code that seems to indicate I would need any upgrades to my system.
Im also wondering about the size of the solar backfeed breaker used. If I want to make the system as flexible for future expansion I might like to use a 200A breaker for the solar backfeed. If I use 705.12(d)(2)(3)(b) 120% for the generation panel then the inverter FLA not the breaker size seems to apply. Is there anything in the code that requires the breaker to be the next size up e.g. 100A rather than oversizing the breaker for future expansion?
In any case, I would be greatful for any feedback on the code interpretation and if I seem to be on the right path.
Thanks,
Kuma
I will be surpassing the limits I can backfeed into the main panel. My load calc is around 100A max so the 200A service is fine, I just need to work around the busbar issue. I am thinking to install a 400a generation panel to take care of the extra solar backfeed. My setup would be:
200A Combo Main panel with feedthrough lugs feeding backfed 200A breaker in a 400A generation panel. No other loads in the main combo meter/panel Per NEC sum of breakers rule 705.12(d)(2)(3)(c).
Solar AC combiner panel with 200A Main breaker feeding the main lugs of the 400A panel at the opposite end of the Generation panel.
Ill be at a little under 100A of backfeed solar, but I am thinking to go with a 200A breaker for future expansion(see question below).
My main house distribution 200A subpanel will be fed by a 200A breaker from the middle of the 400a generation panel.
My question is related to the grounding needs for the system. I currently have sufficient grounding for 200A (2 rods and #4 to them for protection under the older codes), pvc water supply so no bonding, no ties to rebar/concrete.
Im having a challenge interpreting the NEC 250.66 requirements to see if my current 200A grounding is sufficient or I need to upgrade things anywhere in the system.
According to 250.66 which seems to be written from the perspective of a single supply source at the service entrance. It seems that since my service remains at 200A then I should be ok with my current grounding for the GEC based on the 200A service. Actually with only rods it seems #6 would be sufficient as 250.66(a) says the grounding electrode to the rods needs to be #6 max? Even if I did have a 400A service its not clear that I would have to change anything since Im ground rod based?
About the codes, I am uncertain about is that once I start backfeeding solar with multiple sources the theoretical max current goes above the 200A. Most of the wording of the code refers to parallel connections in terms of two parallel conductors to form a larger effective conductor which is much different than mutli source that happens with solar backfeed. I was not able to find any code that seems to indicate I would need any upgrades to my system.
Im also wondering about the size of the solar backfeed breaker used. If I want to make the system as flexible for future expansion I might like to use a 200A breaker for the solar backfeed. If I use 705.12(d)(2)(3)(b) 120% for the generation panel then the inverter FLA not the breaker size seems to apply. Is there anything in the code that requires the breaker to be the next size up e.g. 100A rather than oversizing the breaker for future expansion?
In any case, I would be greatful for any feedback on the code interpretation and if I seem to be on the right path.
Thanks,
Kuma
