Enphase M250 - Installation Sequence Question? Trying to install today 10.18.15.

[Gaff]

I am looking for a bit of reassurance - or a dope slap if necessary - on how I intend to proceed on a Enphase M250 installation .

For several reasons (available daylight, available time, weather, etc.) I intend to install 20 Enphase M250 micro inverters and 20 Solarworld 280W panels (two branch circuits) today and terminate them at an AC sub panel in my attic - then when I have time I will run wire from the main load panel through an AC disconnect up to the AC subpanel in the attic.

This would be out of sequence per the enphase installation manual - but I can't see any harm in doing it this way. Any thoughts on problems I may be opening myself up to would be appreciated!

[inetdog]

I am looking for a bit of reassurance - or a dope slap if necessary - on how I intend to proceed on a Enphase M250 installation .

For several reasons (available daylight, available time, weather, etc.) I intend to install 20 Enphase M250 micro inverters and 20 Solarworld 280W panels (two branch circuits) today and terminate them at an AC sub panel in my attic - then when I have time I will run wire from the main load panel through an AC disconnect up to the AC subpanel in the attic.

This would be out of sequence per the enphase installation manual - but I can't see any harm in doing it this way. Any thoughts on problems I may be opening myself up to would be appreciated!

The main drawbacks that I can see is that you would need to meet the 120% rule in attic panel and in the main panel and that if you do it properly you would have two separate permit fees.

[Ben25]

No problems doing it that way. 120% shouldn't be an issue in the attic either. It would be a 100a, 4 ckt loadcenter backfed to a 30a breaker in the main panel. Only place you have to watch out for 120% is in the main panel if you're running a 100a rated panel with 100a service.

[Gaff]

Thanks for the responses to my post.

I am using a 100 amp subpanel in the attic - each branch will be on a two pole 15 amp breaker. From the subpanel to the main panel I will be running #10 wire through an exterior AC disconnect to a two pole 30 amp breaker in the main panel.

So it sounds like I will be okay if I do not follow the installation sequence provided by enphase. Just finished the wiring on the roof - kind of breezy here today so not sure if I will be able to get the panels up on the roof today - I am working alone so it is a bit of a challenge.

[inetdog]

Thanks for the responses to my post.

I am using a 100 amp subpanel in the attic - each branch will be on a two pole 15 amp breaker. From the subpanel to the main panel I will be running #10 wire through an exterior AC disconnect to a two pole 30 amp breaker in the main panel.

So it sounds like I will be okay if I do not follow the installation sequence provided by enphase. Just finished the wiring on the roof - kind of breezy here today so not sure if I will be able to get the panels up on the roof today - I am working alone so it is a bit of a challenge.

If the only thing connected to the subpanel is the GTI output circuits, it is more descriptive to call it an AC combiner panel instead. Most AHJs will not try to apply the 120% rule to a combiner panel that has no loads connected to it.
But some inspectors will apply the 120% rule anyway, meaning that for a 100A bus with a 100A main breaker the PV cannot total more than 20A.
The easy way to deal with that is to replace the 100A sub main breaker with a smaller (e.g. 60A) main.

[sdold]

The sequence seems OK to me, what is the concern? You'll have the panels connected to the inverters, the inverters connected to the Engage cable, and the Engage cable connected to the sub panel. That's the sequence I used, and the very last thing was running the wiring from the sub panel to the main panel. Unless I'm misunderstanding something, that sounds fine.

[solarddy]

Enphase M250 specs for L1 L2

After testing these Enphase M250 micro-inverters over the past year I have learned a lot as to how they connect, why they connect.
First in answer to your questions, yes you can tie multiple strings or independent micro-inverters together, no it won't short them out, the L1 and L2 on each micro-inverter have a "floating" discovery phase lock, meaning, each M250 will independently analyze the incoming utility sine wave and phase lock on the 0 crossing generating a proper in-phase piggy-back no matter the 180 degrees of the phase. I'm guessing your question comes from tying the two string together. This will not be an issue if your terminal or knobs are rated high enough and are installed properly.

The pin-out of the Enphase M250 AC trunk cable dongle is:

Arrow = Hot L1
next pin= Ground
next pin= Hot L2
Bottom pin = Neutral

You can hook up the Enphase array together before bringing the AC utility service connection, but they will not produce an output until the utility AC voltage of at least 245VAC is sensed by the M250's. Electrically connecting the array together will not harm the panels or the inverters, having an Earth ground to the box and the ground to the rack array frame and panels is a good idea and required by NEC code. The M250's will turn on as soon as they are powered with 22VDC and they will turn off at 18VDC.

Each M250 produces 1A of 245VAC current at best, so a dual-pole breaker of 30A will be adequate @ 120% (25A), although I have seen installations where a dual pole 60A is used as a default, your 100A service panel will be more than enough to handle 20, M250's.

I like that you decided to use the 280 watt panels for the M250's they will turn on sooner and stay on longer than with 250 watt panels. I run 245-300's I like the strong output of the 300's better than the 245's.