Interconnection with using a AC Combiner Panel before Main Service Panel

[PVMatt]

Hi all,

I know I addressed this before. But I do have this discussion with our master electrician (no solar experience) and the inspector who failed us on final inspection because this issue.

The argument of our master electrician is, that the hazard of heat building up at OCPD occurs ONLY at the first OCPD connected to the inverter.
Therefore, he thinks that the 120% rule applies to the AC Combiner panel (if used) and not at the main service panel if we use a AC Combiner Panel. For example, 3 branches of 16 M250 (enphase) each landed at the Ac Combiner Panel with 3x 20 amp breakers (assuming the Ac Combiner Panel bus bar rating in at least 80 amp) and then connect this AC Combiner Panel with a min #6AWG to Main Service Panel (200 amp main breaker and 200 amp bus bar rating) by using a 60amp breaker, is oaky. He refers to Article 705.12.(D)(7).

I believe this is not up to code as the 60 amp breaker landed in the 200Amp Main Service Panel exceeds the 120% rule for interconnection. No matter if the AC Combiner Panel is rated correct and save.

We will have a meeting with local inspector (JEA) and I like to be able to know to what article we have to refer and if the above practice is up to code?

Could you please point me in the right direction here?

Your knowledge and time is highly appreciated J

Regards,

Matthias

 

[PVfarmer]

this is not up to code as the 60 amp breaker landed in the 200Amp Main Service Panel exceeds the 120% rule for interconnection.

You are 100% correct as far as I can tell.
If you had a 225A bus in the main panel, 225 * 1.2 = 270A, so 200A + 60A would be ok by 10A.

But not with a 200A bus.
200 * 1.2 = 240A, so you can add a 40A PV breaker to a 200A panel but not a 60A PV breaker.

 

[GoldDigger]

The idea that heat can only build up at the OCPD closest to the source is totally groundless [sic].
The 120% rule is based on heating of the panel bus by excess current, not the OCPD. And the same current will have the same effect anywhere along the circuit.

mobile

 

[ggunn]

Hi all,

I know I addressed this before. But I do have this discussion with our master electrician (no solar experience) and the inspector who failed us on final inspection because this issue.

The argument of our master electrician is, that the hazard of heat building up at OCPD occurs ONLY at the first OCPD connected to the inverter.
Therefore, he thinks that the 120% rule applies to the AC Combiner panel (if used) and not at the main service panel if we use a AC Combiner Panel.

Your master electrician is mistaken. In the first place (assuming you are operating under the 2014 NEC) the 120% rule does not necessarily apply in the AC combiner. See 705.12(D)(2)(3)(c). You must, however, qualify every bus between the inverter(s) and the service with one of the provisions of 705.12(D)(2)(3). Usually, for every bus other than the AC combiner, it's 705.12(D)(2)(3)(b), i.e., the 120% rule. IMO your master electrician should concentrate on complying with the code as written unless he is also an engineer and feels qualified to weild 705.12(D)(2)(3)(d).