Battery Energy Storage (BESS) Single-Line Diagram: Template & Requirements

A battery energy storage system (BESS) single-line diagram is the document your electrical inspector, your utility, and your fire marshal will all read first. It has to prove three things at a glance: how energy flows between the battery and the grid, where every disconnect and overcurrent device sits, and exactly where your equipment ends and the utility's begins. Whether you're drawing a 13.5 kWh residential wall unit or a multi-megawatt container farm, the same skeleton applies.

This page walks through what a BESS one-line must show, the difference between AC- and DC-coupled topologies, the core power chain component by component, and the protection and interconnection requirements that reviewers look for. Code citations below reference the U.S. NEC and IEEE 1547; the concepts map onto IEC / national wiring rules too. Always verify specific articles against the code edition your authority having jurisdiction (AHJ) has adopted.

What a BESS one-line must show

Regardless of size or topology, a permit-ready storage one-line should identify:

• The energy source — battery bank with chemistry, nominal DC voltage, and usable energy in kWh.
• The power conversion equipment — the PCS (power conversion / control system) or bidirectional inverter, with its continuous AC power rating in kW/kVA.
• Every disconnecting means — DC disconnect(s) between battery and PCS, and the AC disconnect between the PCS and the rest of the system.
• Overcurrent protection (OCPD) — DC-side fusing/breakers and the AC breaker feeding the point of connection, each with ampere and interrupting ratings.
• Metering — revenue and/or production metering as the utility requires.
• The point of interconnection (POI) — the clearly labeled boundary where the customer system ties to the utility (or to a service/main panel).
• Grounding and bonding — equipment grounding conductors and the grounding electrode connection.
• Conductor and conduit callouts — sizes, types, and ratings for each run.

The one-line is a schematic, not a wiring diagram: it shows one line per circuit even where three phases and a neutral exist. Nameplate data, listings, and ratings belong in labels beside each block.

AC-coupled vs DC-coupled: which topology are you drawing?

The single biggest branch in BESS design — and the thing your one-line makes obvious — is whether the battery is AC-coupled or DC-coupled. This matters most when storage is paired with solar PV.

On the one-line the distinction is unmistakable: an AC-coupled system shows two inverters landing on a shared AC point, while a DC-coupled system shows the battery and array meeting on a DC bus upstream of a single inverter. The template further down is AC-coupled because it's the more common configuration and the more general drawing to learn from.

The core power chain, component by component

Read a storage one-line from the battery outward to the grid. The canonical AC-coupled chain is:

battery → DC disconnect → PCS / bidirectional inverter → AC breaker → metering → point of interconnection

• Battery bank. Draw the battery symbol and label the chemistry (e.g. LFP), nominal DC voltage, and usable kWh. For modular racks, note the number of modules and the string arrangement.
• DC disconnect. A load-break-rated DC disconnecting means between battery and PCS lets a technician isolate the stored energy. Many battery products integrate this plus DC OCPD internally — show it either way so the isolation point is explicit.
• PCS / bidirectional inverter. The heart of the system. It converts DC to AC when discharging and AC to DC when charging, and it enforces the grid-support and anti-islanding behavior. Label its continuous AC rating (kW/kVA) and its listing.
• AC breaker / disconnect. An overcurrent device plus a disconnecting means on the AC output. Size it to the inverter's rated output current per the code's continuous-load rules and verify the interrupting rating (AIC) against the available fault current.
• Metering. Depending on the utility and the compensation scheme, you may need a bidirectional revenue meter, a separate production meter, or both. Show the metering location on the one-line even when the utility owns the meter.
• Point of interconnection. The tie to the service. On the load side of the service disconnect this is governed by the interconnection rules of NEC Article 705 (including the busbar/feeder sizing checks such as the 705.12 "120 %" allowance); a supply-side (line-side) tap is the other common option. Label the POI clearly and confirm which method the utility accepts.

Protection, disconnects, and grounding

Storage systems store energy that cannot simply be "switched off" at the source, so the one-line has to make isolation and de-energization obvious on both sides of the converter.

• DC-side protection. A DC-rated disconnect and DC OCPD (fuse or breaker) between the battery and the PCS. Ratings must be DC-appropriate — an AC-only device is not acceptable for DC interruption. Many listed battery units bundle this, but the diagram should still show the isolation point.
• AC-side protection. An overcurrent device on the inverter output sized to the continuous output current, plus an AC disconnecting means. Confirm the device's interrupting rating (AIC) covers the available fault current at that point.
• Rapid shutdown. Where storage shares conductors with a PV array on or in a building, the rapid-shutdown provisions written for PV (NEC 690.12) may apply to those conductors; standalone storage has its own disconnect requirements under Article 706. Treat this as AHJ- and layout-specific and verify before you commit ratings.
• Grounding and bonding. Show equipment grounding conductors bonding all metallic enclosures and the connection to the grounding electrode system. The inverter/PCS usually establishes the grounding reference for its AC output; DC-side grounding (solidly grounded, functionally grounded, or ungrounded) follows the equipment listing and manufacturer instructions — note the scheme rather than assuming one.

The governing article for storage in the NEC is Article 706 (Energy Storage Systems), which covers disconnecting means, overcurrent protection, and installation for ESS; interconnection back to the premises or grid is handled under Article 705. Cite the specific sections only after checking the adopted edition.

Utility interconnection requirements

Anything that can push power back onto the grid triggers an interconnection review, and the one-line is the centerpiece of that application. Expect these themes:

• IEEE 1547. Grid-interactive inverters/PCS must meet IEEE 1547-2018 for interconnection and interoperability of distributed energy resources — including anti-islanding, voltage/frequency ride-through, and the grid-support functions the utility enables. Note the standard and the certified settings on the drawing.
• Equipment listing. Utilities and AHJs generally expect the battery system to be listed to UL 9540 (energy storage systems and equipment), with large-scale fire performance evaluated by the UL 9540A thermal-runaway test method. Reference the listing beside the battery block.
• Utility (external) disconnect. Many utilities require a lockable, accessible, and often visible-blade AC disconnect that utility crews can open to isolate your system. Requirements vary by utility — confirm whether one is mandated and where it must be located, then show it explicitly at the POI.
• Metering and labeling. Bidirectional or separate production metering, plus the placards and directory labels the code requires for parallel power-production sources.

Sizing: power (kW) vs energy (kWh)

A recurring source of confusion on storage drawings is conflating the two ratings that actually size the system:

• Power (kW / kVA) is set by the PCS / inverter. It's how fast you can charge or discharge — the instantaneous rate — and it drives your AC conductor and breaker sizing.
• Energy (kWh) is set by the battery. It's how much you can store — how long you can sustain a given power — and it drives the DC-side design and the physical bank.

Their ratio is the C-rate: a 100 kWh battery paired with a 50 kW PCS is a 0.5C system (about two hours to discharge); the same battery on a 100 kW PCS is 1C (about one hour). Label both numbers on the one-line and make sure the AC-side protection matches the power rating while the battery block carries the energy rating. Reviewers check that these are consistent with the conductors and OCPD you've drawn.

Related

• Solar Interconnection Diagram Examples
• Single-Line Diagram Symbols (IEC + ANSI Cheat Sheet)
• 200 A Residential Service SLD Template

Code references here are general and edition-dependent. Always confirm the specific NEC/IEC articles, IEEE/UL versions, and utility requirements with your AHJ and interconnecting utility before submitting. Questions? Email [email protected].