Combining Micro Inverters: 4 Branches

[Freddyjones39]

I am doing a layout for a system that will use 4 branches in a micro inverter system (APS). I am not entirely sure how to combine the 4 branches. Midnite solar has an AC combiner box for 3 branches (which I have used and is really nice), but nothing larger than that. I would also like to locate the combiner in the attic.

Here is what I am thinking:
-Pull each branch through the roof via a soladeck
-Install a sub-panel in the attic (I'm not sure about code requirements on this one)
-Make the combining happen at the sub panel

Keep in mind... I am in Canada, so the code is a little different, but I am open to NEC related comments as well (in the name of best practice).

[Mike90250]

sigh.
Micro inverters are mounted on the PV panels and you have no DC wires to mess with, just the AC connection harness that goes into conduit and then to the breaker panel.

[Freddyjones39]

I understand that.

I have a number of fairly short branches (because I am mounting on multiple slopes), and I would like to combine them a lot closer to the array instead of pulling 4 cables down to the main panel (and take up a bunch of room in it). Each branch is a low current because they are so short, so I can easily combine them into a reasonable sized conductor and save wire and space in the main panel... Or did I misunderstand what you meant.

If you have 4 branches, what do you use to combine them?

[ButchDeal]

combine the short strings in series. As long as you are below the amperage limit for a string you don't need a combiner. If the total length of all the short branches are over the total amperage, then get a small AC breaker box to combine then, then down to the AC disconnect, then to the MSP.

You can't just take the 4 cables down to the main panel! you need an AC disconnect and only one interconnection point.

[Freddyjones39]

FYI: combining any two short strings will be over the limit for a "series" connection of the branches.

That's exactly what I was wondering. A small breaker box will suffice (installed in the attic).

For my information: Is a single interconnection point required or just best practice?

[ButchDeal]

FYI: combining any two short strings will be over the limit for a "series" connection of the branches.

That's exactly what I was wondering. A small breaker box will suffice (installed in the attic).

For my information: Is a single interconnection point required or just best practice?

you want a small breaker box with a main sized for the combined.
a single interconnect and single AC disconnect located outside near to the meter with labels is required.
Don't you have this on your one line drawing for the permit? and application for interconnect?

[Freddyjones39]

I haven't got the single line yet. I going through the layout to ensure that I don't miss anything.

[sensij]

you want a small breaker box with a main sized for the combined.
a single interconnect and single AC disconnect located outside near to the meter with labels is required.
Don't you have this on your one line drawing for the permit? and application for interconnect?

Although I agree it makes more sense to combine these for one home run, I don't think NEC has a problem with bringing in several PV circuits into the main service panel, each on its own breaker. Rules relating to labeling, service panel rating, and max number of switches/disconnects (6) would still apply.

[ButchDeal]

you would need a single lockable disconnect.
Most locales allow only a single interconnect as well, but the single disconnect is much simpler with a combined line rather than multiple.

[sensij]

That is a local requirement, frequently imposed by the power company or fire department, not NEC. SDG&E, for one, does not usually require it.

[ButchDeal]

In southern ca you usually have external breakers that woud count as accessible disconnect. If not one is generally required.

[sdold]

My POCO and AHJ didn't require an AC disconnect for my microinverter system, and I haven't seen one required in any of the codes. My POCO used to require one, but doesn't anymore. Why do you say he needs an AC disconnect? Is it required in Canada??

[ButchDeal]

Most of the us does though they will count an external breaker especially if MSP is lockable. Canada has varying codes by region but as we have seen most like to see external disconnects. We almost always provide them unless there is reason not to.

[sdold]

What's funny is that the OP wasn't asking about an AC disconnect, he's asking if it's OK to install a sub-panel in the attic with a breaker to each string. That sounds reasonable to me, is there anything wrong with that?

[sensij]

OP asked a follow-up question "For my information: Is a single interconnection point required or just best practice?" That initiated the discussion involving the AC disconnect.

[Freddyjones39]

Thanks everybody for your input. In Canada, from what I can tell, we do not need the discussed AC disconnect (although it isn't unreasonable to install one as mentioned).

I believe all of my questions were answered.