Max Solar System Size for a 125/100 Center Feed Power Panel

[chrisrh]

Looking to install a solar system and I've received several different price quotes. I've noticed a substantial price savings ($1500-$3000 quote dependent) on installation if I don't bother with a electrical panel upgrade. I have a 125 Amp power panel with a 100 Amp center fed main breaker and after consulting with my city's code office, I confirmed they do NOT allow for the 120% rule. I'm limited to 25 Amps. What I haven't been able to figure out with any certainty is what size solar system can I support with only 25 Amps to work with? Would it make any difference if microinverters were used instead of a string inverter? I'm sold on Enphase 250's on the microinverter side, while I like the Sunny Boy line of inverters if I go the conventional route. Appreciate any help.

[PVAndy]

Looking to install a solar system and I've received several different price quotes. I've noticed a substantial price savings ($1500-$3000 quote dependent) on installation if I don't bother with a electrical panel upgrade. I have a 125 Amp power panel with a 100 Amp center fed main breaker and after consulting with my city's code office, I confirmed they do NOT allow for the 120% rule. I'm limited to 25 Amps. What I haven't been able to figure out with any certainty is what size solar system can I support with only 25 Amps to work with? Would it make any difference if microinverters were used instead of a string inverter? I'm sold on Enphase 250's on the microinverter side, while I like the Sunny Boy line of inverters if I go the conventional route. Appreciate any help.

hy don't they allow the 120% rule? i would challange that. It's been in the code for several cycles. Are you saying if you have a 200A Main panel with a 200A Buss mo backfeed is allowable? I would ask to see this rule in writing/ Of course can always do a line side tap with a fused disconnect.

Andy

[CA_Tom]

hy don't they allow the 120% rule? i would challange that. It's been in the code for several cycles. Are you saying if you have a 200A Main panel with a 200A Buss mo backfeed is allowable? I would ask to see this rule in writing/ Of course can always do a line side tap with a fused disconnect.

Andy

My guess is the city's code office is telling him that center-fed bus means 120% rule is not allowed / doesn't apply.

And careful with the "always" - line side tap is disallowed in my jurisdiction (or at least the guidelines they give out for how to submit for a permit explicitly says it's not allowed)


AS for the original question:
25A * 80% * 240V = max 4.8kW inverter (I think)

[Mb190e]

Does anybody know the reasoning behind the local building departments that don't allow line side taps? I have a 200 amp service panel with no room for breakers to backfeed so my installer used line side taps with a 60 amp fused disconnect.

[SunEagle]

Does anybody know the reasoning behind the local building departments that don't allow line side taps? I have a 200 amp service panel with no room for breakers to backfeed so my installer used line side taps with a 60 amp fused disconnect.

It seems that there is a wide variety of what is acceptable to a local building department in the US. Each State, County and Town seem to follow a different set of rules.

Based on some of the feedback in this Forum, I have seen some discussion where they are very strict with what and who does the work to the other side of the pendulum where "you look pretty smart go ahead and do what you want".

It is amazing that when it comes to safety there is a wide understanding of what work can be performed and what should be performed.

[J.P.M.]

It seems that there is a wide variety of what is acceptable to a local building department in the US. Each State, County and Town seem to follow a different set of rules.

Based on some of the feedback in this Forum, I have seen some discussion where they are very strict with what and who does the work to the other side of the pendulum where "you look pretty smart go ahead and do what you want".

It is amazing that when it comes to safety there is a wide understanding of what work can be performed and what should be performed.

Some of that may hinge on what some folks, including you I think, have observed in some way or another: 2 rules - 1.) The inspector is always right. 2.) If the inspector is wrong, see rule #1.

[SunEagle]

Some of that may hinge on what some folks, including you I think, have observed in some way or another: 2 rules - 1.) The inspector is always right. 2.) If the inspector is wrong, see rule #1.

Unfortunately those rules have been what I have experienced more than a few times.

[J.P.M.]

Unfortunately those rules have been what I have experienced more than a few times.

Me too. I think they're ubiquitous.

[inetdog]

It may not be just the local AHJ that has the problem with line side taps.
Since the wires connect upstream of the main service disconnect your POCO has a legitimate reason to be involved and some of them do not allow line side taps for whatever reason.
If it is just the AHJ, though, they should have some local ordinance in writing to back them up, since the NEC does not put any limitations on properly wired line side taps.
Depending on where the mythical "service point" is located, the POCO may not have any jurisdiction either, but they have the power just the same.