Service Size Calculation

[JoergK.]

Hello,

I am planning to increase my 10kWh PV system to 18 kWh.

My service is 208 V 3ph, 200 AMP main panel, 200 AMP service from my line co.

The inspector said that my potentially 89 AMP, (call is 100 AMP) production from 18 x APSYSTEMS YC1000 would need to be added to my main panels size of 200 AMP and I need a 300 AMP main breaker panel.

Is this calculation correct? Would I not substitute purchase power with my own production, not adding it to it?

Help and/or explanation would be great.

Thanks,

Joerg K.

 

[Danke]

It’s for the busbar rating usually. One the way around that is a line side tap.

For all load-side interconnections, the 120% rule states that the main service breaker rating plus the sum of 125% of the inverter ampere rating shall not exceed 120% of the main service panel busbar rating.

(Busbar Rating (A) x 1.2) - Main Breaker Rating (A) = Max (PV + Battery) (A)

 

[Bkord]

How is your system hooked up. It may be a buss bar limitation. There are ways around that.

 

[JoergK.]

Thanks Danke & Bkord,

The power comes from the meter to a non fused switch to go to line or a generator, center position is disconnect it carries on to a 225 Amp 3ph splitter and the 200 amp main panel (I assume the busbar?). Can I go of the splitter with a 100 amp fused disconnect to my PV breaker panel?

 

[Shimmy]

Do you have a circuit breaker between the meter and the non-fused transfer switch?

If so, if you can replace the wiring between the 225A transfer switch and the panel, you can tap those wires with your new PV feed. That would need to be rated about 300A assuming all 200A circuit breakers.

 

[JoergK.]

Yes, 200 amp. The distance from the transfer switch to the splitter is 4', so right underneath the transfer switch. the 200 amp breaker panel is also right above the splitter, to the right of the transfer switch. My wire size calculator says # 12 copper or #10 alu wire and we have #2 alu.

 

[Shimmy]

My wire size calculator says # 12 copper or #10 alu wire and we have #2 alu.

Um... get a new wire size calculator. 200A is 3/0 copper or 300MCM aluminum.

If you wanted to tap in the PV conductors you need 250MCM copper or 400MCM aluminum, and a 100A breaker where you make the tap for the PV. This is most easily done with a Polaris multi-port tap set.

 

[JoergK.]

Well, I got egg on my face.

My chief electrician was out today and did the calculations quickly and we also looked the amp's up for the the Apsystems YC1000-3-3 and it is 3.14 amp for the 208 V inverter and 1.35 amp for the 480 V.

So, 18 (YC1000-3-3 on 208) x 3.14= 56.52 amp. Presently I have a 60 amp breaker, but may change it over to a 70 amp to allow for the 80% rule.

All wiring is good and suitable. Just should have looked at the YC1000 spec. sheet more carefully.

Thanks for the help you fellows gave.

All the best,

Joerg K.