Run from Microinverters to Backfeed Breaker, how do ya do it?

[jmoles]

For running wire from the microinverters to the backfeed breaker can I just run straight to the backfeed breaker?

For permitting purposes I don't need a rapid shut down, the microinverters cover it. For functional purposes can I just run all my wires to the needed junction boxes, into the conduit, and then bring it to the back feed breakers?

 

[zanydroid]

For running wire from the microinverters to the backfeed breaker can I just run straight to the backfeed breaker?

For permitting purposes I don't need a rapid shut down, the microinverters cover it. For functional purposes can I just run all my wires to the needed junction boxes, into the conduit, and then bring it to the back feed breakers?

Microinverter AC wiring is largely just like regular house wiring in rules. Needs to be sized at 125% but really just follow the branch circuit size for the microinverter type. The rules are relaxed under the array, in that area you can use trunk cable outside of conduit where usually you can’t do that in the house.

20A and 30A are common. 15A is possible but might as well just do 20A.

Now if you are installing Enphase you’re supposed to land in their official combiner box so it can do some control and monitoring magic. Since their instructions say to do it this way, you need to comply for code and permitting purposes.

(But this is not needed for a electrically functioning or safe system)

 

[zanydroid]

Now the backfeed breaker positioning and size limits are subject to design and sizing rules in 705.12

 

[pvgirl]

You can just run to the back feed breaker, you will need to consider the rating of your panel and main breaker to stay within the limits for how much solar you can connect per NEC 2020 705.12(B)(3)
For rapid shutdown you will need to make sure there is a disconnect mounted outside to initiate rapid shutdown. This can disconnect the whole house or just the inverter output circuits. Also there may be requirements for an outside disconnect from your power utility.

 

[zanydroid]

I would recommend clarifying what the exact disconnect rules are for POCO and AHJ. Possibly by asking local neighbors with solar and looking at what they have.

I had plans set that had a much more expensive method for disconnecting microinverters than my POCO/AHJ allows. Fortunately I had installed a system before at that address so I knew it was not needed.

I believe if using Enphase putting the combiner box outside will probably satisfy most local rules.

 

[jmoles]

I think my POCO interconnection agreement does require a disconnect outside. With my AHJ I think the microinverters cover the rapid shutdown requirement but I'll check back with them.

I mainly wanted to make sure there wasn't an additional breaker box that was needed for safety or function before going to the MSP - which sounds like Enphase does call for.

Currently I'm looking at Hoymiles or APsystems microinverters. I'd get a gateway/monitoring so I'll look over their install manuals to see how they need to be hooked up.

 

[zanydroid]

I think my POCO interconnection agreement does require a disconnect outside. With my AHJ I think the microinverters cover the rapid shutdown requirement but I'll check back with them.

Most places require an external disconnect. And it's also something EG the fire department cares about.

Microinverters cover rapid shutdown under NEC, however there's a question here on the specifics of how it's triggered. With microinverters the low level mechanism is always the same -- cut the AC feed so it can't see grid anymore. But where you put the breaker/switch for that is the question.

I mainly wanted to make sure there wasn't an additional breaker box that was needed for safety or function before going to the MSP - which sounds like Enphase does call for.

Some random reasons you would want a combiner subpanel:
- organizing cables
- lots of branch circuits, and AHJ is anal about how they interpret 120% rule (branch circuits need to be on opposite end)
- might be easier to monitor combined solar output with energy meter if you put one CT on combiner feeder vs snaking multiple branch circuits into the same CT. I have both setups in my system.
- 705.12 min-maxing

In the past (like, 2011 or 2008) the combiner simplifies most 705.12 calculations. Nowadays it only simplifies some less common calculations.

Currently I'm looking at Hoymiles or APsystems microinverters. I'd get a gateway/monitoring so I'll look over their install manuals to see how they need to be hooked up.

I haven't looked at APsystems. I use Hoymiles. I have their monitoring and installed to their rules.

Hoymiles monitoring (DTU or DTU-S) is all wireless based, so they don't need a combiner box like Enphase which is power line communications based. (The Enphase combiner probably has some CTs in it or something as well for various purposes).

I have two hoymiles branches going into an inside combiner (this was from an installer). And another two hoymiles branches going into distribution subpanel (inside as well; this was my self-install). But my POCO/AHJ allows us to cut off the whole house on shutdown, lol. Some places require independent solar shutdown.

 

[jmoles]

Most places require an external disconnect. And it's also something EG the fire department cares about.

Microinverters cover rapid shutdown under NEC, however there's a question here on the specifics of how it's triggered. With microinverters the low level mechanism is always the same -- cut the AC feed so it can't see grid anymore. But where you put the breaker/switch for that is the question.


Some random reasons you would want a combiner subpanel:
- organizing cables
- lots of branch circuits, and AHJ is anal about how they interpret 120% rule (branch circuits need to be on opposite end)
- might be easier to monitor combined solar output with energy meter if you put one CT on combiner feeder vs snaking multiple branch circuits into the same CT. I have both setups in my system.
- 705.12 min-maxing

In the past (like, 2011 or 2008) the combiner simplifies most 705.12 calculations. Nowadays it only simplifies some less common calculations.



I haven't looked at APsystems. I use Hoymiles. I have their monitoring and installed to their rules.

Hoymiles monitoring (DTU or DTU-S) is all wireless based, so they don't need a combiner box like Enphase which is power line communications based. (The Enphase combiner probably has some CTs in it or something as well for various purposes).

I have two hoymiles branches going into an inside combiner (this was from an installer). And another two hoymiles branches going into distribution subpanel (inside as well; this was my self-install). But my POCO/AHJ allows us to cut off the whole house on shutdown, lol. Some places require independent solar shutdown.

As I’m looking at disconnects I’m realizing I’ll probably need to combine the branches before I get to the disconnect. I have two branches each need to be on its own circuit. All the combiner boxes I’m coming across seem to be made for DC. How does the Hoymiles disconnect work for the microinverters? Do they run to a panel box with breakers then to the disconnect Then to the backfeed panel?

 

[pvgirl]

As I’m looking at disconnects I’m realizing I’ll probably need to combine the branches before I get to the disconnect. I have two branches each need to be on its own circuit. All the combiner boxes I’m coming across seem to be made for DC. How does the Hoymiles disconnect work for the microinverters? Do they run to a panel box with breakers then to the disconnect Then to the backfeed panel?

You can just use any load center as the combiner for AC micro inverters.

 

[jmoles]

Hm. So something like this with the 2 breakers and going to a disconnect. Are there products that simplify this so I don’t need to do two boxes?

If the breaker box is outside and accessible that may be considered the disconnect. I guess I’d need to check with my POCO / AHJ.

 

[zanydroid]

How does the Hoymiles disconnect work for the microinverters?

Not sure what you mean by Hoymiles disconnect. There is no special HoyMiles hardware.

Yes in the U.S. you would just combine the branch circuits with a subpanel.

You only need that snap disconnect if your AHJ wants it for uniquely local virtue signaling purposes. I would start the bidding with them (discussion on the phone or office hours, worst case initial plans submission) at the exterior service disconnect you already have, no special separate box. Then escalating to:
1) subpanel with only combiner breakers, feeder landing on lugs with no OCPD
1A) same, but with feeder landing on main breaker so you can disconnect all with one throw. You will need to be careful with 120% rule here, and may end up using sum of breakers (colloquial name for two separate 705.12 sections
1B) if AHJ really wants snap disconnect skip the main breaker

Hoymiles does 30A branch circuits. Note that if you really do need to combine branch circuits you have a very high chance of exceeding the 120% rule limits.

Did you call AHJ and POCO yet or ask a locally specific question on an appropriate forum where solar owners/diyers in your town will see? I see exterior disconnect and what kind as a simple yes/no question anyone can answer for you, so no big deal. But having enough microinverter branch circuits to run into busbar rating limits requires doing real math and design to figure out.

What is the reason to go microinverter?

 

[jmoles]

What is the reason to go microinverter?

Partial shading issue at the install site. That’s the primary, if not entire, reason. I haven’t really looked at a string inverter w/ optimizers.

This stepped approach w/ AHJ is a good idea. I like to have the worst case scenario in mind before I start, to try to calculate total costs and just know what I could run into and how to handle it if/when I do.

 

[zanydroid]

The worst case will be the combiner plus big disconnect switch. IMO if they force you to get a disconnect you should use a decent quality one or a circuit breaker. Since those are definitely well tested in passing current through them all the time.

Optimizers potentially cause trouble (DIY information on debugging them is pretty poor). If you have many hours of shading in mid day going without optimizers will force the matching to go through and heat up bypass diodes which are harder to replace than optimizers. I don’t know if TIGOs end up sharing the bypass current with the diodes, that would be good for spreading the pain around

For microinverters converting to a ESS will be a little less efficient and require more fundamental cost, since the ESS needs to have an AC charger / inverter rated to the same size as the microinverters. And the DIY options for this are not great right now, but improving way faster in my opinion than optimizers