Hi guys,
I was hoping to get a little feedback on a solar installation as it relates to load calcs and service panel sizing. The plan is to install a 7.200 kW system (18 panels x 400 watts) with microinverters and I have 2 questions:
1) Is the main panel adequate to support the planned PV output?
2) Why is the city requiring the addition of 40 amps to the residential load calc amperage?
1) Is the main panel adequate to support the PV output?
=====================================
Main panel is an Eaton MBED2040PV125BF
bus = 225 amps
main breaker = 125 amps
Per the "120% rule" the maximum PV output the panel can support is:
((Busbar Rating (A) x 1.2) - Main Breaker Rating (A) )/1.25 = Max PV (A)
Max PV (A) = ((225 amp x 1.2) – 125 amp) / 1.25 = 116 amp
Max PV (kW) = 116 amp x 240 / 1000 = 27.84 kW
Since this is well beyond the planned system of 7.2 kW, I believe this is more than adequate and no derating is required etc. - could this be confirmed please?
2) Why is the city requiring the addition of 40 amps to the residential load calc amperage?
===========================================================
When submitting a permit application to install an EV charger, the city's load calculation form shows all of the standard entries by square footage, appliances max. of non-coincident loads etc.
But at the very end of the form they have included a line labelled "40 amp back-feed protection for future PV system (solar panels) +40 Amps".
So basically they requiring the addition of 40 amps to the calculated loads.
Does this really make sense? I did a fair amount of googling and nowhere else do I see any versions of the NEC load calcs that include this. I have a feeling this is not correct. Any thoughts/feedback would be appreciated.
Thanks
Dennis
I was hoping to get a little feedback on a solar installation as it relates to load calcs and service panel sizing. The plan is to install a 7.200 kW system (18 panels x 400 watts) with microinverters and I have 2 questions:
1) Is the main panel adequate to support the planned PV output?
2) Why is the city requiring the addition of 40 amps to the residential load calc amperage?
1) Is the main panel adequate to support the PV output?
=====================================
Main panel is an Eaton MBED2040PV125BF
bus = 225 amps
main breaker = 125 amps
Per the "120% rule" the maximum PV output the panel can support is:
((Busbar Rating (A) x 1.2) - Main Breaker Rating (A) )/1.25 = Max PV (A)
Max PV (A) = ((225 amp x 1.2) – 125 amp) / 1.25 = 116 amp
Max PV (kW) = 116 amp x 240 / 1000 = 27.84 kW
Since this is well beyond the planned system of 7.2 kW, I believe this is more than adequate and no derating is required etc. - could this be confirmed please?
2) Why is the city requiring the addition of 40 amps to the residential load calc amperage?
===========================================================
When submitting a permit application to install an EV charger, the city's load calculation form shows all of the standard entries by square footage, appliances max. of non-coincident loads etc.
But at the very end of the form they have included a line labelled "40 amp back-feed protection for future PV system (solar panels) +40 Amps".
So basically they requiring the addition of 40 amps to the calculated loads.
Does this really make sense? I did a fair amount of googling and nowhere else do I see any versions of the NEC load calcs that include this. I have a feeling this is not correct. Any thoughts/feedback would be appreciated.
Thanks
Dennis