April 11, 2023

Power Control Systems and the National Electrical Code

Learn why Power Control Systems are increasingly important for solar photovoltaics (PV), energy storage, and electric vehicle infrastructure.
SEAC Assembly Member and Enphase Energy Director of Codes & Standards Mark Baldassari

At the March 2023 SEAC general meeting, SEAC Assembly Member and Enphase Energy Director of Codes & Standards Mark Baldassari presented on the technical capabilities of power control systems (PCS) and applications permitted in the National Electrical Code (NEC) and the UL 1741 Standard for inverters, controllers and other equipment used with grid-interactive distributed energy systems.

This article summarizes several key points from Baldassari, who originally proposed adding PCS to the NEC at the Photovoltaic (PV) Industry Forum in 2016 and led the inclusion of PCS in the 2020 edition of the code.

We will highlight how PCS can eliminate the need for main electric service panel upgrades when adding energy storage to existing PV systems. We will also note that PV systems with PCS can add far more generating capacity than would otherwise be permitted by code.

PCS can also limit power exports to the grid and imports from the grid, adjusting to changes in net energy metering that affect the return on investment of PV and energy storage systems. Thousands of systems in Hawaii are making use of PCS to comply with successor tariffs for distributed energy resources after Hawaii ended the use of net energy metering.

Baldassari says it won’t be long before many U.S. homes will be using PCS to control power flows, adding energy storage and enabling various electric vehicle (EV) applications to support power flow between the vehicle, the home, and the grid.

What Are Power Control Systems?

NEC 2020 Section 705.13 is so important to Baldassari that, after formal adoption, he considered getting the number 705.13 tattooed on his forehead. It’s a good thing he didn’t. The NEC 2023 update incorporated new code sections, as we’ll soon discuss.

But first, let’s start with some definitions.

Power control systems control the output of one or more power production sources, including PV systems, batteries, and EVs.

Within the system, they limit current and loading on busbars and conductors. They also limit current to the ampacity of the conductors or busbar ratings.

Instead of relying on the main breaker to trip, PCS can limit power flow from one or more circuits so current does not exceed rating limit in the first place.

This has meaningful implications for system sizing. In many cases, adding storage to an existing residential PV system would overload circuit breaker rating requirements. You need to upsize the PV system breaker. The busbar doesn’t accept more ampacity. Seemingly, this forces a panel upgrade.

Technically, PV systems have long had a way of curtailing inverter output or adjusting when batteries are charging or discharging. But there was nothing in the code that allowed it.

That’s where the idea of adding PCS to the NEC came from.

System designers commonly oversubscribe the busbar because not all power sources and loads are operating at capacity at the same time.

With PCS, you can limit how much power is going to the busbar at all times, making it possible to significantly increase capacity of distributed energy resources connected to the panel.

Instead of oversubscribing by 20 percent, you can go up to the busbar rating. That means up to 200 amps (A) on a 200 A breaker.

Changes in 2023 NEC

If you look up Section 705.13 in the 2023 NEC, you will notice the term Power Control Systems has been replaced with a new term, Energy Management Systems, and it takes you elsewhere in the Code to Section 750.30. Baldassari says this term “kind of takes you further away from what it really does.”

The 2023 code updated Section 750.30, called load management. This section sets conditions on the monitoring and control of electrical loads and sources. Baldassari says load management is a “misleading term” and the initial part of this section “gets lost in the weeds” before PCS re-enters the fold.

The public comment period for updates in the 2026 NEC is open, now through early September. In the months ahead, SEAC’s National Electrical Code working group will lead the development of code change proposals.

UL 1741 Updates

Meanwhile, technical experts have been developing a series of changes to UL 1741 that will also affect PCS deployment.

In 2019, UL published a Certification Requirements Decision (CRD) covering terms and requirements for evaluations and listing of PCS products. A technical committee, an advisory group previously known as a standards technical panel, has reviewed and commented on the CRD.

Revisions based on technical committee comments are due to be published later this year. The revisions will then be integrated into UL 1741 as part of the published standard.

One use case for PCS is to have a single controller limiting ampacity on the main busbar. Another use case envisioned by the next iteration of UL 1741 integrates multiple controllers that communicate with each other while carrying out different functions.

On a branch circuit, PCS make it possible to oversubscribe power production sources the same way PCS allows you to oversubscribe sources on the main busbar. PCS can also limit current to allow for more generation or load connected to the busbar on a subpanel and a feeder going back to the main panel.

In addition to allowing multiple PCS functions and control points within a PCS, UL 1741 changes provide for the use of circuit controllers to allow the use of uncontrolled sources and loads within a PCS.

Maybe you want to heat water or run a pool pump while you have excess generation. Or maybe you want to interrupt power to an air conditioner at times when it’s more important to conserve a battery for other uses.

UL 1741 changes also create a new scheduling function for power export limiting and pave the way for power import limiting. You can adjust settings according to time of day or month of the year. There’s a lot of flexibility built into the revised standard.

Improving the Code

There are many ways to improve the code, starting with informing industry peers about what’s permitted under the 2020 NEC and the 2023 NEC.

While discussing Baldassari’s presentation at the March general meeting, Pete Jackson, SEAC Steering Committee Member and Chief Electrical Inspector in Bakersfield, California, said his department processes about 200 residential PV and energy storage permit applications per week, some of which incorporate service panel upgrades.

“In terms of now having two supplies, [from PV and energy storage], that panelboard PCS eliminates 100 percent of the needs of all the systems I’m seeing for panel upgrade,” Jackson says. “That’s what I keep telling the integrators around here. You could avoid panel upgrades completely if you can make use of PCS.”

To learn more about Article 705 updates in the NEC and much more, register for the IAEI Southwestern Section Meeting & Tradeshow, Aug. 27-31, in Bakersfield, and attend the Aug. 29 panel discussion “ESS vs. Generators,” featuring Schneider Electric’s Chad Kennedy, who serves on NEC Code-Making Panel 13, along with several SEAC members and other industry experts.

You can also view and participate in the development of UL standards. Visit UL Solutions’s Collaborative Standards Development System site. There you can view details about proposals, technical committees, information on how to participate in the standards development process, and more. Fill in the contact form at the bottom of the SEAC homepage with any questions.

Lastly, join SEAC’s next general meeting on April 27 at 3:30pm Eastern for updates on the 2026 code change proposals under consideration by SEAC’s National Electrical Code working group. See details in the event calendar at our Get Involved page.