Key takeaways
- An energy storage plan set is scoped by NEC 2023 Article 706, which applies to any permanently installed energy storage system over 3.6 MJ (1 kWh) — essentially every residential battery.
- NEC 2023 706.15 drives two separate devices: an ESS disconnecting means, and, at one- and two-family dwellings, an emergency shutdown initiator outside the building marked off or on.
- UL 9540 is the listing standard for the system. UL 9540A is a thermal runaway test method, not a listing, and a plan checker wants that report only to justify relief from a spacing or capacity limit.
- Siting comes from the residential and fire codes, not the NEC: units capped at 20 kWh, 3 ft apart, aggregate caps set by the room.
- Backup panel load calculations and service panel de-rating are not part of Avila Solar Drafting’s standard PV + Energy Storage Plan Set. They are ordered separately.
An energy storage plan set is a PV plan set plus everything the battery adds: an ESS listed to UL 9540, a disconnecting means and emergency shutdown per NEC 2023 706.15, a siting plan that satisfies capacity and separation limits, and a single line diagram redrawn around the transfer point and the protected loads panel. Here is what each of those looks like on paper.
What does an energy storage plan set show that a PV-only set doesn’t?
A storage package carries five things a PV-only set never has to: an ESS listing and nameplate capacity, an ESS disconnecting means and emergency shutdown device, a siting plan proving capacity and separation compliance, a transfer point with a protected loads panel on the single line diagram, and a resolved answer to how the service busbar accommodates a second source. Everything else — cover sheet, site plan, roof plan, structural details, placards — carries over.
The sheet count barely changes. What changes is the density of each sheet and the cross-references a plan checker has to reconcile. On a PV-only job the reviewer verifies one source against one busbar. On a storage job there are two sources, an island-mode condition, and a physical installation the fire code has an opinion about. Closing that gap is what our PV and storage plan sets are built for.
One consequence is worth stating up front: on a storage submittal, the fire code drives where the equipment physically lands, and that has to be settled before the electrical design is finished.
For the sheet-by-sheet anatomy of the underlying package, see our breakdown of the six-sheet PV permit package. This piece assumes that baseline and covers only what storage adds. For which NEC article governs what across Articles 690, 705, 706 and 710, start there instead.
Which NEC article covers energy storage systems?
NEC Article 706 covers energy storage systems. Under NEC 2023 706.1, the article applies to permanently installed energy storage systems having a capacity greater than 3.6 MJ (1 kWh), whether stand-alone or interactive with other power production sources. That is worth naming on the cover sheet, because NEC 2017 706.1 used a voltage test instead — over 50 volts AC or 60 volts DC.
Scope is now decided by energy, not voltage. A 48-volt residential battery a 2017-cycle reviewer might have argued into Article 480 as a stationary battery installation sits squarely inside Article 706 under the 2023 cycle. Naming the adopted cycle on the drawings ends that argument before it starts.
Article 706 is not the only one in play. NEC 2023 Article 690 governs the PV side, Article 705 the point of interconnection, and Article 710 island-mode operation. A storage plan set citing only 706 is incomplete.
- NEC 2023 706.1 — scope by capacity, greater than 3.6 MJ (1 kWh).
- NEC 2023 706.15 — disconnecting means, plus emergency shutdown at dwellings.
- NEC 2023 706.7 — commissioning on installation for other than one- and two-family dwellings, a note that belongs on commercial solar PV designs, not on a house.
The 2017-to-2023 gap on Article 706 is wide enough that a template built for the wrong cycle reads as an error rather than a difference. Confirming the cycle first is the same discipline that governs other jurisdiction-specific permitting requirements.
What does NEC 706.15 require for ESS disconnects?
NEC 2023 706.15(A) requires a means to disconnect the ESS from all wiring systems, including other power systems, utilization equipment and its associated premises wiring. NEC 2023 706.15(B) requires that means to be readily accessible, and adds an emergency shutdown function at one- and two-family dwellings with an initiation device outside the building that plainly indicates off or on. Both are physical devices on the site plan and symbols on the single line diagram.
The “all wiring systems” language is stronger than it looks. Opening the AC output breaker is not enough: the means has to isolate the ESS from every source and load it touches. On a DC-coupled system with a shared hybrid inverter, the drawings must show how the PV input, the battery DC circuit and the AC output are each addressed.
NEC 2023 706.15(E) adds a disconnecting means for the battery circuit itself, with its marking, where batteries sit separately from the ESS electronics. On a modular rack that is a real device on a real wall, and it needs a location, not a note.
The exterior emergency shutdown device under 706.15(B) is the item most often missing from a first submittal. It is distinct from the ESS disconnect and the PV rapid shutdown initiator, even though all three may land on the same wall. Reviewers check that placard content and device labeling agree — the same detail that governs PV disconnect placement.
Show all three — ESS disconnect, battery disconnect where applicable, emergency shutdown initiation — as separately tagged, dimensioned devices. Undimensioned equipment is one of the most common plan set mistakes.
Is UL 9540 the same thing as UL 9540A?
No, and conflating them collects a correction notice. UL 9540 is the Standard for Energy Storage Systems and Equipment — the listing an ESS carries. UL 9540A is a test method for evaluating thermal runaway fire propagation, and it produces a report, not a listing. Your plan set needs the first as a matter of course, the second only when you are asking for relief from a code limit.
UL Solutions describes UL 9540 as covering “electrical, electrochemical, mechanical and other types of energy storage technologies for systems intended to supply electrical energy” — the integrated system, not the battery alone. The listing belongs to the system as configured, which is why swapping a component after the plans are drawn can invalidate the listing you cited.
UL 9540A is separate. UL Solutions calls the 9540A method “the American and Canadian national standard for assessing fire propagation related to thermal runaway events in battery energy storage systems,” and the only consensus standard explicitly cited in NFPA 855 for large-scale fire testing.
| Document | What it is | When the plan set needs it |
|---|---|---|
| UL 9540 listing | System listing for the ESS as configured | Always — cite the listing and attach the cut sheet |
| UL 9540A test report | Large-scale fire test data for that product | Only when spacing or capacity exceeds the prescriptive limit |
Cite the UL 9540 listing on the cover sheet and in the equipment schedule. Attach a UL 9540A report only when the layout depends on it, and say on the sheet which limit it buys relief from.
Where can the battery go, and how much can you install?
Location and quantity are governed by the residential and fire codes, not the NEC. Under the 2021 IRC Section R328 and NFPA 855, individual residential ESS units are limited to 20 kWh, units must be separated from each other by at least 3 ft, and aggregate capacity is capped by location — 40 kWh in utility closets, basements and storage spaces, and 80 kWh in garages and detached structures. Those figures come from UL’s bulletin for code authorities on 2021 residential ESS requirements, which also notes that smaller separations and larger ratings are permitted where documented by a UL 9540A test report.
Location restrictions matter as much as quantity. ESS units are generally not permitted in sleeping rooms, in closets or spaces opening into sleeping rooms, or in habitable spaces. Outdoor units carry their own separation from doors, windows and gas meters, hence the elevation sheet.
Working space is an NEC requirement, not a fire code one. NEC 2023 110.26(A) sets the clearance in front of equipment likely to be examined while energized: 3 ft deep, 30 in wide, 6 ft 6 in of headroom. In an attached garage with a vehicle in it, that envelope is frequently what forces the battery to a different wall.
AHJ handouts make this concrete. The City of Palo Alto’s residential energy storage handout requires the site plan to identify the proposed ESS alongside existing PV, ESS or EV charging equipment, and elevations when it sits outside. The Seattle Fire Marshal’s Office ESS checklist asks for a room layout diagram with battery spacing clearly denoted. Draw those dimensions; do not note them.
How does the single line diagram change when a battery is added?
The single line diagram gains a second source, a transfer point and usually a second panel. It has to show the ESS nameplate power and energy rating, the ESS disconnecting means, the microgrid interconnect device or transfer equipment that separates the premises from the utility during an outage, the protected loads panel and its schedule, and the busbar arithmetic proving the interconnection is legal. Five new elements on the densest sheet in the set.
The transfer point is the conceptual change. On a PV-only single line the utility is always present. On a storage single line there is an island-mode condition where the system separates from the grid and supplies a defined subset of the premises. The drawing must show which loads sit inside that island.
Interconnection is where storage jobs stall. NEC 2023 705.12(B)(3)(2), the 120 percent allowance, still applies, but two sources now share the busbar. Three pathways exist when the arithmetic fails:
- De-rate the main breaker so the main plus the source breakers fits the 120 percent allowance. This requires proving the calculated service load sits below the new main rating.
- Connect on the supply side of the service disconnect per NEC 2023 705.11, which takes the busbar out of the equation entirely.
- Use a listed power control system under NEC 2023 705.13, which limits current dynamically so the connection complies without a panel change.
Each is a different drawing and a different set of supporting documents. Choosing late turns a two-day drafting job into a three-week permitting job — which is why interconnection is one of the design decisions before you draw.
When do load calculations and service de-rating become mandatory?
A load calculation becomes mandatory in three situations: when you de-rate the main breaker to make the busbar arithmetic work, when the AHJ requires one on any ESS submittal as policy, and when the system backs up the whole premises rather than a defined subset. The Palo Alto handout cited above lists one as a submittal item outright.
De-rating is the most common trigger. Drop a 200 A main breaker to 150 A to fit a second source on the busbar and you have made a claim about the building: its calculated load does not exceed 150 A. NEC 2023 Article 220 is where that gets proven, by the standard method or NEC 2023 220.82’s optional method for dwelling units. A de-rated main with no calculation behind it draws a correction.
Whole-home backup is the second trigger. NEC 2023 Article 710 governs stand-alone and island-mode operation, and backing up an entire premises means the ESS carries the calculated load while islanded — not the main breaker nameplate, and not a guess. That is a second calculation, distinct from the interconnection one. Decide up front, and order it with the plan set.
The scoping fact worth knowing before you order: Avila Solar Drafting’s standard PV + Energy Storage Plan Set does not include backup panel load calculations or service panel de-rating. Those are ordered separately from the Professional Engineering menu, where Electrical PE (Load Calcs) is a discrete line item that can be bundled with PV + Storage. The same split applies to standby work, where our residential generator plan sets carry NEC 2023 220.82 optional load calculations as their own package option.
Worked example: adding storage to a maxed-out 200 A service
An existing 7.6 kW PV system on a 200 A service with a 200 A main breaker. The customer now wants two 13.5 kWh battery units in the attached garage with a partial backup panel.
Start with the busbar. The 120 percent allowance on a 200 A busbar is 240 A. The PV inverter delivers 31.7 A continuous, sized at 125 percent to a 40 A breaker. The ESS power conversion equipment is also 7.6 kW, so it takes its own 40 A breaker. That is 280 A against a 240 A allowance. It does not fit.
De-rate to 150 A and it works: 230 A, inside the allowance. But that 150 A main is a load calculation waiting to be proven under NEC 2023 Article 220. If the calculated load comes back at 165 A, the de-rate is off the table and you are back to NEC 2023 705.11 or 705.13.
Now the physical install. Two 13.5 kWh units is 27 kWh aggregate — inside the 80 kWh garage cap, each unit inside the 20 kWh cap. But they must sit at least 3 ft apart unless a UL 9540A report documents less, and NEC 2023 110.26(A) still wants 3 ft of depth and 30 in of width in front of each disconnecting means. On a two-car garage wall with a vehicle in it, that often pushes one unit outdoors — adding separation from doors and windows, plus an elevation sheet.
Order of operations matters. Resolve siting and separation first: it sets conductor routing. Then the interconnection method: it decides whether a load calculation is required. Then draw. Teams that draw first and site second redraw the single line twice, and the pre-submittal checklist catches it too late.
FAQ
Which NEC article covers energy storage systems?
NEC Article 706 covers energy storage systems. Under NEC 2023 706.1 it applies to permanently installed systems over 3.6 MJ (1 kWh). NEC 2017 706.1 used a voltage test instead, so confirm the adopted cycle before drafting.
Where can the NEC requirements for stationary battery installations be found?
In NEC Article 706 for energy storage systems, and NEC Article 480 for stationary standby batteries outside that scope. Under the 2023 cycle the dividing line is capacity: over 3.6 MJ (1 kWh) lands in 706.
What are the NEC requirements for battery storage disconnects?
NEC 2023 706.15(A) requires a means to disconnect the ESS from all wiring systems, including other power systems, utilization equipment and associated premises wiring. NEC 2023 706.15(B) requires it to be readily accessible and adds an emergency shutdown at one- and two-family dwellings, initiated outside the building.
Is UL 9540A a listing?
No. UL 9540A is a test method for evaluating thermal runaway fire propagation; it produces a report. UL 9540 is the listing standard for the system itself. Attach a 9540A report only when the layout needs relief from a prescriptive limit.
Does an energy storage plan set include a load calculation?
Not in Avila Solar Drafting’s standard PV + Energy Storage Plan Set. Backup panel load calculations and service panel de-rating are ordered separately from the Professional Engineering menu. Order one with the plan set when the design de-rates a main breaker or backs up the premises.
What changed for energy storage between the 2017 and 2023 NEC?
Scope. NEC 2017 706.1 applied Article 706 by voltage, over 50 volts AC or 60 volts DC. NEC 2023 706.1 applies it by energy capacity instead, greater than 3.6 MJ (1 kWh).
Order a PV and storage plan set
Storage jobs rarely stall on drafting. They stall on siting decided after the electrical design, or a de-rated main with no load calculation behind it.
Avila Solar Drafting builds permit-ready PV and storage plan sets in 2–3 business days, backed by our guarantee of accurate solar plan sets and six months of free revisions from the order date. Every ESS package is drawn against the code cycle your AHJ has actually adopted, with disconnecting means, emergency shutdown and separation dimensions on the sheet rather than in a note.
Need the load calculation or the de-rating analysis with it? Add Electrical PE (Load Calcs) from the Professional Engineering menu when you place the order. For commercial ESS or an unusual siting condition, call 971-410-0655 and we will scope it directly.
