[RE-wrenches] ESS and Calculated Load in Texas

Sat Aug 2 11:17:39 PDT 2025

We are still on NEC 2020, but I had this issue with a jurisdiction here
recently, and I am just going to cut and paste my winning argument here for
your benefit. Take from it whatever you think might help. My permit was
issued less than an hour after sending this.

--------

Dear [Insert Misinformed Plan Reviewer Name Here],

I think you are still misinterpreting the scope of Article 702. This is a
common issue that was cleared up in the 2023 language, where they removed
the phrase you are referring to after it caused mass confusion in the 2020
version. Here is why Article 702 does not apply (and others do):

*(all bold, italic, and underlined emphasis below is added by me)*

The system we are installing is connected in parallel with the utility
source, which is covered by Article 705, *Interconnected *Electric Power
Production Sources. Section 705.2 defines a Microgrid-Interconnect Device,
which in this case is the Enphase System Controller. If you look at the
last paragraph of Section 705.40, Loss of Primary Source, an interconnected
source is permitted to operate in *island mode* when the primary source is
lost. Head over to Section 710.1 where the scope for Stand-alone Systems is
defined. This is the Article where island mode is discussed. That is why
the governing section for this installation with respect to loads is 710.15(A),
which allows for an *islanded* system to have less capacity than the
calculated load.

Article 702 does not apply here as that covers standby systems, and this is
not a standby system. This is an islandable interconnected power source. A
standby system is one that does not function in an interactive manner with
the utility grid. The reason storage batteries were added to this section
is that you *can* have storage batteries that are *not* capable of
interacting with the utility grid, but *do* supply standby power, as is the
case of an Uninterruptible Power Supply (UPS). This would also be the case
if you have batteries with a multimode inverter with an integrated transfer
switch that disconnects from the grid during an outage to supply selected
loads, but does not "sell" power to the grid. That type of backup system
*would* need to comply with Article 702 because it is not an interconnected
power source. It is simply a load with respect to the primary power source
(utility).

By the way, side note... Enphase also offers a Sunlight Backup Only system,
which uses microinverters with the same System Controller, but no battery
whatsoever. It only provides power during the day to the extent that there
is enough solar irradiance available to loads. This is a perfect example of
why Article 710 rules in the case of an islanded interconnected system. It
is not a standby system. The solar power supply is variable, necessitating
the system to function at a capacity that is less than the connected load.
A microgrid is a very different system than a standby system. A microgrid
can be comprised of various sources of power, which can include utility,
batteries, solar, generators, and others. The major distinction between
Articles 705 and 702 is the Microgrid Interconnect Device. Article 702
relies upon a transfer mechanism with no interactive component.

I hope that clears it up. We code nerds in the industry saw this coming,
but it is pretty clear once you make the distinction between an islanded
interactive system versus a standby system.

Article 710 is small, but mighty!

--------------

Jason Szumlanski
Principal Solar Designer | Florida Solar Design Group
NABCEP Certified Solar Professional (PVIP)
Florida State Certified Solar Contractor CVC56956
Florida Certified Electrical Contractor EC13013208

On Sat, Aug 2, 2025 at 1:56 PM Chris Sparadeo via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Hi all,
>
> I’m finding out that some jurisdictions in Texas are requiring ESS output
> to be equal to or greater than the calculated load of a dwelling. For
> example, if backing up the whole home, and the service load is calculated
> at 150A, the ESS would require to continuously output 150A OR EMS is
> required to bring the calculated load to or below that of the ESS. AHJ’s in
> a few areas of Texas are dying on this hill and to actually meet the
> calculated load, systems would need to be significantly larger than needed.
>
> I know that previous versions of 706 (specifically NEC 2017) could lead
> one to argue this point, but Texas had adopted NEC 2023, and it’s only
> article 710 that indicates a system operating in isolation of the grid
> should has sufficient output to supply load to the largest backed up load.
>
> Has anyone run into this issue? And if so, what have people been doing to
> either meet these outdated requirements or successfully push back?
>
> Thanks!
>
>
> Chris Sparadeo
>
> VT Master Electrician # EM 08220
> C_802-369-4458
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