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I am trying to fulfill my one line drawing for AEP Texas for their interconnection agreement so I can install solar with battery backup on our home.

AEP says:

  1. Please note that the AC Disconnect cannot be connected directly to the meter; it must go thru the service panel. One Line will need to be revised.
  2. NOTE: If a side line tap is done the AC Disconnect must be fused; otherwise non-fused.

REQUIREMENT BY AEP THAT THE AC DISCONNECT CANNOT BE INSTALLED DIRECTLY TO THE METER; MUST BE INSTALLED THROUGH THE SERVICE PANEL AND THEN ALL ALTERNATIVE GENERATION INSTALLED BEHIND.

I'm installing (plan to) 2 Sol-Ark 15K inverters which are to connect: meter > safety switch > inverters

AEP is telling me I need to have the load center feeding the safety switch which defeats the operation of the safety switch in providing isolation for AEP's line workers.

AEP wants:

(Meter) - (Load Panel) - (Emergency Cutoff) - (Sol-Ark 15K inverter) - (somehow back to the load center (they DO NOT Specify)) (which creates a circle)

Sol-Ark website link (reference page #13)

Is there anything in the code concerning having the Emergency Cutoff switch directly after the meter?

My question is: Is there anything in NEMA code which prevents the location of the safety switch directly off of the meter?

Any help will be greatly appreciated. AEP does not quote any regulations for their insistence concerning their denial based on the Safety Switch coming off of the meter.

Sol-Ark installation diagram for 2 inverter setup: Sol-Ark installation diagram for 2 inverter setup

Image of my current setup. The graphic is covering a 200A 240V breaker box with feed thru lugs which was installed for a different anticipated solar installation. things have changed and I'm trying to correct the setup based on Sol-Arks manual and installation recommendations.

various electrical boxes on the outside of the house for the current set up

Image of my line diagram based on Sol-Ark 15 inverter manual

Image of my line diagram based on Sol-Ark 15 inverter manual

HI, My confusion is the reference to the Sol-Ark manual, which shows a direct connection from meter to safety switch to inverters. My only gripe about having a load center is that now I have a piece of equipment taking up the space where my Safety switch was planned and that it will not be part of the electrical during power outages. To my misunderstanding. The safest location to insure the protection of line workers is having the switch right after the meter. I acquiesce to you wisdom and will have to move some thing to get that safety switch withing 3 feet.

Also from AEP in their interconnect agreement: item

(5. Company will make on-site visits to verify the proper installation and continuing safe operations of the generating facilities. This includes the required installation of an external AC disconnect switch ( blade type, not a breaker) which is within three feet of the meter, readily available to the Company, and lockable. if more than one inverter is used, feed all inverters through a single, common external AC disconnect. –

  1. the point of common coupling of the renewable generating facilities is preferred to be behind the main disconnect for the service fo which the renewable generation is interconnected.)

The Sol-ark is capable of 200 A 240V service. I would not want to break off subsections of the home for wiring and standby power generation. We have a 14K diesel genset, the Sol-Ark will carry 30K of panels and we intend to also install 30K of LiFePo4 batteries

SOl-Ark 15 inverter sol-ark.com/sol-ark-15k-all-in-one My installation type is on page 13 of the manual.

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  • The locals can do what they want, even going against NEC. So you need to follow the local regulations. Most places you can use NM/romex cable, a few you are not allowed to, must use conduit.
    – crip659
    Oct 4, 2022 at 18:40
  • It's important to remember that the NEC has no legal force whatsoever by itself. It only has force when localities write laws/regulations that say "thou shalt follow NEC version <year>" - and they are 100% free to say "thou shalt follow the NEC, except do it this other way in cases X, Y, and Z".
    – nobody
    Oct 4, 2022 at 23:20
  • Is there a reason you want to put your whole house on the Sol-Arks instead of having them feed a separate standby bus? Oct 5, 2022 at 3:06
  • @JohnCindy987 -- are you wedded to the Sol-Ark platform btw? it isn't the only game in town, especially when you factor in having the genset... Oct 5, 2022 at 22:08
  • @ThreePhaseEel -- Yeah, I like the 15K model, I can tie my strings directly in to the inverters, they can handle the whole casa for load and 2 can handle 30K of power to help drop my electric bill. I have great infrastructure here in the sticks, so in a year I've only had the gen on for excersize. I have many energy users here, I'll probably add another 15K in a year or so depending on actual impact. Oct 6, 2022 at 23:46

1 Answer 1

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They are not saying "(Meter) - (Panel with all of your house's circuit breakers) - (Emergency Cutoff) - (Sol-Ark 15K inverter) - (somehow back to the panel with all your house's circuit breakers)". That would be absurd.

They are saying "(Meter) - (Main Disconnect+breaker where neutral is bonded to ground) - (Emergency Cutoff) - (Sol-Ark 15K inverter) - (subpanel with all your house's circuit breakers)".

The old way

This is so due to NEC rules. NEC defines the "Service Disconnect" as the place, where the Ground Rods meet the Ground Conductor and the neutral-ground equipotential bond happens. They don't care if you put some branch circuit breakers there too. And I just described your average, run-of-the-mill service panel pre-NEC-2020, which lacks a standby generator.

The new way

However in NEC 2020 they changed the rule to require the Service Disconnect outdoors. The practical implementation of that is to have a "Meter-Main", which is a combo meter pan + main breaker. The main breaker provides the NEC-mandatory disconnect. The ground bonding happens there, and from there you have a 4-wire feeder to the "Master Supanel" where all your breakers are. You don't want a literal knife switch disconnect right after the meter and then a traditional main+breakers load center, because a problem in that knife switch could see 10,000 amps of totally unfused service current.

How that works with backup inverters

Consider the new paradigm vs. the inverter you want to install. Suddenly, BOOM! It's easy. The inverter simply installs between the "Meter-Main" and the "subpanel with all your branch circuit breakers".

The trick is -- when you add solar to that, the power is now bidirectional on the line between inverter and meter-main. That is, at night you draw power from utility, and by day you feed power back to the utility. Hold that thought.

The power company's requirements are obsolete

Consider the traditional solar system Before Sandy (the hurricane). A solar system simply fed power from solar to grid - one-way flow. It tied in anywhere past the meter, and so it was easy to stick a disconnect switch there, and that disconnect didn't affect anything but the solar.

This is the paradigm your power company is stuck on. Their requirement is designed on the presumption that all generated power will come down "the line from the solar panels" which will be 30A, 50A or 70A at the absolute outside. Thus, it's "not a big ask" to require that come through a regular old knife switch that they can pull, and lock, to assure that your generation is offline.

After all, that will only take your solar offline, it's not like they're shutting down your whole house! LOL! Perfectly reasonable. Makes sense.

However...

Hurricane Sandy knocked out power to a million of the most powerful people in the world, who figured with the fortune they had just spent on a solar system, surely that must power their house during outages! Well. This rude awakening created enormous market pressure for exactly the kind of hybrid system you are installing.

The 1-connection problem with the knife switch

But your system wants to take one (1) connection from the grid and then be bidirectional on it. This makes the inverters cheaper but the transfer switch much more complicated.

And as you are discovering, this style of inverter does not play well with your utility's knife switch rule. They can't reconcile the fact that it is both a backup power generator (which never matters to them because it's walled off by an interlock) and a grid-tied solar supply.

I don't know what to tell you about this. The root problem is that their "knife switch" rule is stupid, since the concept of it being easy is wrong now. However, the system that you got is not compatible with the knife switch rule, so it was a bad choice for this utility. And that's the fault of the company who specced this system. This is their mess, and you should push back on them to have them sort it out. Maybe they can spec other gear.

I mean as things stand, to move forward with this gear, you'll need a 200A knife switch on your entire service. But pulling that will disconnect your entire house from the grid, which is not what the rule ever intended. Blame the rule, blame bidirectional feed. Either way.

It isn't helping matters that you appear to be holding onto the "security blanket" of that ratty old generator, so that too must be integrated into the system, or according to that diagram you posted, worked around. It's setup so that when the solar/battery gives out, the ATS automatically switches to 1978 (the year) and the battery system is locked out. There is no provision for the generator to recharge the batteries.

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    @JohnCindy987 The power company rules only consider old simple solar, that generated to the grid only and simply shut down when the grid is down. They are "behind the times" and have not considered the PowerWall and other modern solar+battery+grid-down power+dump-to-grid systems. Basically to shut them up, I would just give them their knife switch right after the meter-main. I still say "meter-main" so the knife switch is protected by a breaker. (there is no breaker on the utility side of your meter. Really. The wires are sized so their resistance limits current to 10,000 amps. That's it.) Oct 5, 2022 at 19:56
  • Your edit "To clarify, the inverter will charge batteries if the battery low voltage is exceeded. "4-Stage Charging The MPPT has a 4-stage battery charging algorithm for rapid, efficient, and safe battery charging." So "ratty" will do its job for emergency time too." appeared to be a reply to the answer. Under StackExchange's system, that should be a comment. Keep in mind StackExchange is not a forum, it works differently to try to solve the poor signal/noise ratio typical of discussion forums. But if you prefer the forum format, try diychatroom.com. Oct 5, 2022 at 23:23
  • As to the meat of your comment, the generator will not charge the batteries, since per your drawing it will not be connected to the battery at all. They are on opposite legs of the transfer switch. It would be possible to have a separate battery charger attached to the generator side of the transfer switch and attached directly to the batteries, thus DC-coupling around the transfer switch. However the big generator is wildly oversized for the battery charging task, so would not be efficient. Oct 5, 2022 at 23:34
  • True I do not have the gen connection to the batteries on my diagram. I'm in enough trouble already, but yes they will tie in eventually to charge the batteries. Sorry. Oct 6, 2022 at 1:48
  • My apologize, for not understanding the workings of this system. Oct 6, 2022 at 1:52

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