Template · 9 min read · Updated June 2026

EV Charging Station Single-Line Diagram (Load Calc + Template)

Every EV charging project — a pair of Level 2 stations in a condo garage, a workplace lot, or a highway DC fast-charging site — runs into the same question at plan review: does the electrical service have room for the load, and can you prove it? A single-line diagram (SLD) is the drawing the utility and the authority having jurisdiction (AHJ) use to answer that. This guide walks the power chain from the service down to each charger, shows how to size the circuits under NEC Article 625, and gives you a template you can open and edit for free.

The code references here are based on recent editions of the National Electrical Code (NFPA 70). Code adoption varies by state and city, and later editions renumber sections — always verify the specific article numbers and values against the code edition your AHJ has adopted.

Draw an EV charging single-line on smartsld.com — free

Why an EV project needs a one-line

Two reasons, and both show up early:

Permitting. Most AHJs require a single-line diagram plus a load calculation as part of the electrical permit for fixed EV supply equipment (EVSE). The SLD is what shows the reviewer the service rating, the overcurrent protective devices (OCPD), conductor sizes, the disconnecting means, and exactly how the chargers tie into the existing distribution.
Service-capacity check. EV charging is a large continuous load. The one-line, paired with an Article 220 load calculation, is how you demonstrate that the existing service and panel can carry the added demand — or justify a service upgrade or a load-management device instead. Skipping this step is the most common reason EV permits get kicked back.

The SLD also carries the coordination information a reviewer looks for: interrupting ratings (AIC) on the OCPDs, the grounding and bonding path, and the voltage/phase at each stage.

The power chain: service to EVSE

Every EV charging site is the same backbone with chargers hung off the end. Draw it top to bottom:

Utility service — the incoming supply. Label voltage, phase, and frequency (e.g. 120/240 V 1Ø for a house, 208Y/120 V or 480Y/277 V 3Ø for a commercial site).
Revenue meter — utility metering. Some sites add a separate meter or sub-meter for the EV load so charging energy can be billed or tracked.
Service disconnect / main breaker — the main OCPD. Its ampere rating sets the ceiling for everything downstream.
Panel or switchboard — the distribution bus. Level 2 chargers typically land on a normal 208/240 V panel; a bank of DC fast chargers may need its own switchboard, a step-down or step-up transformer, or even a dedicated service.
EVSE branch circuits — one dedicated circuit per charger, each with its own OCPD, disconnect where required, and the EVSE itself at the end.

Here is that chain drawn out for a small commercial site with three Level 2 chargers and one DC fast charger:

Small commercial EV site: 480 V service and switchboard feed one DC fast charger directly and a step-down transformer feeds a 208 V panel with three Level 2 branch circuits. Ratings shown are illustrative — size everything to your actual equipment and code.

Sizing the circuit: NEC 625 and the 125% rule

The single most important fact for EV work: EV charging is a continuous load. NEC Article 100 defines a continuous load as one whose maximum current is expected to continue for three hours or more, and a car typically charges for hours at a steady current. That triggers the 125% rule.

NEC 625.41 requires the branch-circuit overcurrent device and the conductors to be sized for continuous duty at no less than 125% of the EVSE's maximum load. So you never size a charger circuit to the nameplate current alone — you multiply by 1.25 first.

Worked example for a common 48 A Level 2 unit (e.g. a hardwired 48 A wall connector):

EVSE maximum load: 48 A
Minimum OCPD / circuit rating: 48 × 1.25 = 60 A breaker
Conductor: sized for the 60 A circuit per the NEC 310 ampacity tables and any adjustment/temperature-correction factors — verify with the AHJ

For the service and feeder load calculation, use Article 220. Recent code editions add a dedicated EVSE demand rule — NEC 2023's 220.57 calculates the EV load at 7200 VA or the equipment nameplate rating, whichever is larger — so confirm which method your adopted edition uses. The output of the load calc is the number the reviewer cares about: total calculated demand versus the service rating.

Level 2 vs DC fast charging

These are electrically different animals, and the SLD makes the difference obvious.

Attribute	Level 2 (AC)	DC fast charging (DCFC)
Supply	208 or 240 V, single-phase (or line-to-line off a 3Ø panel)	Commonly 480 V 3-phase; smaller units at 208 V 3Ø
Typical current	~16 to 80 A per unit	Tens to hundreds of amps; often a dedicated feeder
Power	~3.3 to 19.2 kW	~24 kW to 350+ kW
Where conversion happens	AC delivered to the car; the vehicle's onboard charger rectifies to DC	The station rectifies AC→DC internally and delivers DC straight to the battery
On the SLD	Ordinary branch circuit off a panel	Large feeder, frequently its own switchboard/transformer or service

Because a DC fast charger does the AC-to-DC conversion inside the cabinet, it is a large, power-electronics load. On bigger sites the DCFC units often justify a separate 480 V switchboard — or a distinct utility service — rather than sharing a panel with lighting and receptacles. Connector standards (CCS, NACS/SAE J3400, CHAdeMO) affect the plug and the car, not the one-line, but note them on the drawing for the site designer.

Load management: adding chargers without a service upgrade

The math often lands badly: sum the EVSE loads at 125%, add them to the existing Article 220 demand, and the total blows past the service rating. The traditional answer is an expensive service upgrade. The modern answer is load management.

NEC 625.42 permits an energy management system (EMS) or automatic load management system (ALMS) to set the maximum EV load on a service or feeder. When such a system is used, the maximum equipment load counted on the service or feeder is the value the load-management system is set to enforce — not the raw sum of every charger at full output. The broader EMS rules live in Article 750.

In practice, an ALMS monitors the total current and throttles or staggers the chargers so the aggregate never exceeds the setpoint. That lets you install more charging capacity than the service could carry if every unit ran flat out at once — which they rarely do. On the SLD, show the load-management controller, the current-sensing point, and the setpoint it enforces, because the reviewer will size the service against that setpoint. Confirm the listing and settability of the specific device with your AHJ.

Disconnecting means, GFCI, and CCID protection

Two protection topics show up on nearly every EV plan check:

Disconnecting means. NEC 625.43 requires a disconnecting means for EVSE rated above 60 A or more than 150 V to ground, installed in a readily accessible location and capable of being locked in the open position. Smaller units may not need a separate disconnect, but many designers add one anyway for serviceability — check the threshold in your edition.
Personnel protection (GFCI / CCID). Listed EVSE includes an integral charge-circuit interrupting device (a CCID, commonly CCID20 tripping around 20 mA of ground fault) per the product listing standard. Separately, receptacle-fed (cord-and-plug) EVSE and general receptacles may require GFCI protection under NEC 625.54 and 210.8. Hardwired listed EVSE relies on its built-in CCID rather than a panel GFCI breaker — but verify the requirement for your configuration with the AHJ, since it depends on how the unit connects.

Don't forget grounding and bonding: show the equipment grounding conductor with each branch circuit and the connection back to the grounding electrode system at the service.

Multiple chargers on a shared feeder

Fleet depots and multi-space lots put many chargers behind one feeder. Two rules shape how you draw it:

Each EVSE gets its own branch circuit. NEC 625.40 requires each outlet or piece of EVSE to be supplied by an individual branch circuit that serves no other load. So on the one-line, every charger has its own OCPD — you don't daisy-chain two chargers on one breaker.
Group the branch circuits on a feeder or sub-panel. The individual charger circuits land on a dedicated EV panel or switchboard, and that assembly is fed by one feeder. Absent load management, size the feeder for the sum of the connected EVSE at 125%. With an ALMS (625.42), size it to the enforced setpoint instead — this is where load management pays off on multi-charger sites, because real fleets almost never charge every stall at full power simultaneously.

Draw the EV sub-panel branching off the main bus as a single feeder with its own OCPD, then show each charger circuit as a separate drop inside that group — exactly like the three Level 2 circuits in the template above.

Open the free editor and draw your EV charging one-line in minutes

Code values and section numbers change between NEC editions and local amendments — treat everything here as a starting point and confirm with the current code and your AHJ. Spotted an error? Email [email protected].