Question about wiring multiple arrays in grid-tie micro inverter system.

Frankie_Bones
Frankie_Bones Registered Users Posts: 5
Greetings, I am trying to calculate the cost of putting in a 40 panel grid tie system with enphase microinverters. The system will be comprised of 3 arrays. A 15 panel roof mount south facing array, a 15 panel east facing roof mount array and a 10 panel south facing array mounted on an fully engineered pergola. I was wondering how the 3 240v ac lines are wired? Do they each require a separate disconnect and circuit breaker in the panel or are they combined and then routed to a single disconnect and circuit breaker?
Thanks
Frankie

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Question about wiring multiple arrays in grid-tie micro inverter system.

    I believe the answer is--Each 20 amp 240 VAC circuit needs its own breaker.

    And, depending on the code/utility requirements for your area, you may need a lockable outside disconnect for your solar array power (my utility used to require this, but no more--They trust that Listed GT inverters are not dangerous to their workers).

    So--Either you will need three AC disconnects, or you can run the three 20 amp circuits to a sub panel and wire the 60+ amp circuit through a disconnect on your outside/accessible wall, then to a 60+ amp circuit+breaker in your main panel (of course, your main panel has to support your GT Inverter following current NEC rules for your AHJ).

    The hardware costs are not that great (breakers+box+disconnect)--And the cost of the wire will be similar (three smaller 20 amp circuits vs one larger 60+ amp circuit).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Question about wiring multiple arrays in grid-tie micro inverter system.

    In my locale it is having an AC combiner to join the 3 20 amp circuits which feeds an accessible single throw disconnect and then a back-feed breaker. Mine also has a PV production meter required by the utility.
  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
    Re: Question about wiring multiple arrays in grid-tie micro inverter system.

    Also be aware that unless your electrical service panel is greater than 200A you are not likely to be able to install a system of that size without some extra electrical work. A supply side connection or a service upgrade may be necessary. If you are lucky you may be able to simply downsize your existing main breaker. This is not DIY stuff for most people.
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Question about wiring multiple arrays in grid-tie micro inverter system.
    jaggedben wrote: »
    Also be aware that unless your electrical service panel is greater than 200A you are not likely to be able to install a system of that size without some extra electrical work. A supply side connection or a service upgrade may be necessary. If you are lucky you may be able to simply downsize your existing main breaker. This is not DIY stuff for most people.

    Yep this is true, a 200 amp buss bar has to be lowered to at least 180 amps or less grid input. The exception would be if the manufacturer gives the buss bar a higher rating. For instance, a 200 amp panel might have a 225 amp buss bar in it.

    But be prepared for a battle with the inspector and have the documentation at the ready.
  • Frankie_Bones
    Frankie_Bones Registered Users Posts: 5
    Re: Question about wiring multiple arrays in grid-tie micro inverter system.

    Here is my panel, as I understand it the sum of circuit breakers feeding the system can not exceed 120% of the busbar rating. So would I be able to drop the main breaker to a 180a and then add either a single 60a or 3 20a breakers from the pv to the bus bar for a total of 240 amps? Also in addition to the solar disconnect located near the service panel I would like to add disconnects near each of the 3 solar arrays so I can de-energize the lines between the solar panels and the breaker box. How is this normally accomplished, switches, breakers? Is this overkill?
    Thanks.
    Attachment not found.
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Question about wiring multiple arrays in grid-tie micro inverter system.
    Here is my panel, as I understand it the sum of circuit breakers feeding the system can not exceed 120% of the busbar rating. So would I be able to drop the main breaker to a 180a and then add either a single 60a or 3 20a breakers from the pv to the bus bar for a total of 240 amps? Also in addition to the solar disconnect located near the service panel I would like to add disconnects near each of the 3 solar arrays so I can de-energize the lines between the solar panels and the breaker box. How is this normally accomplished, switches, breakers? Is this overkill?
    Thanks.
    Attachment not found.


    So have you applied for a permit yet? (do you even need to in your jurisdiction. ) They will be the final say as to what is allowed in your design. Also talk to the utility as they will most likely need to be involved and will have requirements.

    An AC combiner panel can provide you 3 breakers to act as individual shut offs.
  • Frankie_Bones
    Frankie_Bones Registered Users Posts: 5
    Re: Question about wiring multiple arrays in grid-tie micro inverter system.

    I have not applied for a permit yet as I do not have a final design to submit to the building department. My goals are to have 40 panels spread over 3 arrays. I want a clean installation with a majority of the wiring ran through the attic and walls and a minimal amount of conduit and disconnect panels mounted on the house. I don't understand why PG&E would require a lockable/visible ac disconnect with on a microinverter system which by design will not back feed a service line with an outage.
  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
    Re: Question about wiring multiple arrays in grid-tie micro inverter system.
    Here is my panel, as I understand it the sum of circuit breakers feeding the system can not exceed 120% of the busbar rating. So would I be able to drop the main breaker to a 180a and then add either a single 60a or 3 20a breakers from the pv to the bus bar for a total of 240 amps?

    You would have to find a 175A breaker (the next standard size down) that matches the type that is currently installed. You may also want to confirm with Eaton (i.e. Cutler Hammer) that it is acceptable for an electrician to replace the main breaker; in some cases doing may void the UL listing. You don't want to be unprepared if your inspector asks about this.

    I see you are in PG&E territory. With them you should be able to install 3 20A breakers and avoid the cost of an extra disconnect. However it looks like you may not have quite enough space in your panel for that.

    Note that if you give up just 6 panels you can avoid all these issues and simply install two 20A breakers. That would be a much simpler install.

    One more thing: the code requires you to move all those existing breakers upward and install your solar at the bottom (opposite end from the main).
    Also in addition to the solar disconnect located near the service panel I would like to add disconnects near each of the 3 solar arrays so I can de-energize the lines between the solar panels and the breaker box. How is this normally accomplished, switches, breakers? Is this overkill?
    Thanks.

    Not necessarily overkill. Just a bit of extra cost. Some jurisdictions I've worked in have required it. IMO whether it's worth it depends mostly on how far the arrays are from the service panel, and thus how much hassle would be avoided and safety gained if you have to work on the arrays. With Enphase you can disconnect an inverter from the trunk cable instead (keep that tool!) to service it or a panel.