EV charging load management: sizing a site without a service upgrade (NEC 625.42, CEC 8-500)

A DC fast charging site is sized by what the dispensers draw from the grid. A Level 2 site is sized by a code floor that has little to do with the equipment: NEC 220.57 counts every space at 7,200 VA or the nameplate rating, whichever is greater, and NEC 625.42 makes that load continuous with no demand factor behind it. Two hundred Level 2 spaces calculate as 1,440 kVA and 1,732.1 A at 480Y/277 V, landing on a 2,500 A main and a 2,000 kVA transformer — for a garage that will never see 200 cars at full power. Load management is the code-recognised way out. An EVEMS holding the same site to 400 kW takes the transformer from 2,000 kVA to 500 kVA, a factor of four. Both cases are worked below under the NEC and the CEC, with the setpoint derived from energy rather than optimism. These are the rules behind the EV charging service capacity calculator. Figures follow the editions cited; local amendments, the engineer of record and the AHJ govern any installation.

What does the NEC actually count as the EV load?

Three clauses set the number, and none of them offers diversity.

NEC 220.57 governs the EVSE load in the feeder and service calculations of Article 220. The load is 7,200 VA or the nameplate rating, whichever is larger. The floor matters more than engineers expect: a 32 A unit on a 208 V commercial supply is rated 32 × 208 = 6,656 VA, below the floor, so it still calculates at 7,200 VA — 8.2 percent of load that exists only in the code.

NEC 625.40 requires an outlet installed to supply EVSE to be served by an individual branch circuit.

NEC 625.42 supplies the classification that drives everything downstream, stating that electric vehicle charging loads “shall be considered to be continuous loads,” and that the overall rating of the installation may be limited through controls only as permitted by 625.42(A) or (B). The device and conductor rules in 210.20(A) and 215.3 then apply the familiar 125 percent multiplier. Unlike lighting or receptacle load, no demand factor in Article 220 reduces an EVSE count.

Four relations carry the rest:

Load per space = the greater of 7,200 VA and the EVSE nameplate rating

S = N × VA_space ÷ 1000

I = S × 1000 ÷ (√3 × V)

OCPD ≥ 1.25 × I

S_transformer ≥ S ÷ 0.80

The last line is a loading convention rather than a clause, and the kVA steps it rounds into are the ANSI C57.12 ladder; both are set out in how to size a transformer. The direct-current case, where AC input rather than DC output sets the load, is worked in DC fast charging site sizing.

What do NEC 625.42 and CEC 8-500 allow a controller to do?

Both codes let a listed control system replace the connected load with a smaller, enforced ceiling. They differ in how far the relief goes.

The two entries that decide a project are NEC 625.42(A), where the EMS setpoint becomes the load, and CEC 8-106 11), where the EVSE load can be removed from the calculation. Everything else is bookkeeping around those two sentences.

Worked example — 200 Level 2 spaces at 480Y/277 V

Given: a 200-space parking structure, one 32 A 208 V Level 2 EVSE per space, a 480Y/277 V service from a utility primary, and a 10-hour overnight charging window.

1. Load per space. Nameplate is 32 × 208 = 6,656 VA. NEC 220.57 takes the greater of that and 7,200 VA, so the calculated load per space is 7,200 VA.
2. Connected EVSE load. 200 × 7,200 = 1,440,000 VA = 1,440 kVA.
3. Service current. I = 1,440,000 ÷ (√3 × 480) = 1,440,000 ÷ 831.38 = 1,732.1 A.
4. Main device. The load is continuous, so 1,732.1 × 1.25 = 2,165.1 A. The next standard rating in NEC 240.6(A) is 2,500 A, on a 2,500 A bus.
5. Transformer. 1,440 ÷ 0.80 = 1,800 kVA, and the next standard three-phase rating is 2,000 kVA.
6. Branch circuits. Each 32 A EVSE is continuous, so 32 × 1.25 = 40 A, giving a 40 A branch device per space under NEC 625.40 and 210.20(A).

A 2,000 kVA transformer and a 2,500 A lineup for a commuter garage is what the code produces when nothing controls the load — and what triggers a utility service upgrade, typically a significant cost and schedule item.

How do you choose the EVEMS setpoint?

The setpoint is an energy question, not a power question. The site does not need to deliver 1,440 kVA; it needs to deliver a quantity of kilowatt-hours inside a window.

P = N × E ÷ (η × t)

with E the design energy per vehicle-day, η the charging efficiency from the meter to the battery, and t the usable window. Taking E = 18 kWh, η = 0.90 and t = 10 h for the 200-space garage:

Close the loop: 400 kW × 0.90 × 10 h = 3,600 kWh, divided by 200 vehicles, is 18.0 kWh each — the design input, recovered. Level 2 EVSE draws at essentially unity displacement power factor, so the 400 kW setpoint is carried through the sizing below as 400 kVA; state that assumption on the one-line. Under NEC 625.42(A) that ceiling, enforced by an EMS complying with 750.30, is the load on the service and the feeder.

The service current falls to 400,000 ÷ 831.38 = 481.1 A, and 481.1 × 1.25 = 601.4 A. That is 1.4 A above the 600 A step in NEC 240.6(A), so the main lands on 700 A. Backing the setpoint down closes the gap — and because this is a ceiling, the result must be truncated rather than rounded up:

A 399 kVA cap — a quarter of a percent less energy — keeps the whole lineup one frame size smaller. Check the other end of the range too: with all 200 ports active the per-port share is 400,000 ÷ (200 × 208) = 9.6 A, which must stay above the minimum current the selected EVSE and its control pilot can hold. Where it would not, the EVEMS has to sequence ports rather than throttle all of them, and that behaviour belongs in the specification.

Load management earns its keep at workplace and fleet sites where vehicles dwell for hours, at retrofits where spare capacity is thin, and on phased rollouts. It earns less where every port must deliver rated power on demand.

What does the same garage look like under the CEC?

This is where Canada diverges, and the divergence runs in both directions.

The basis is different. The CEC sets no per-space minimum in volt-amperes. EVSE enters the calculation at its connected rating, taken at a 100 percent demand factor, under the occupancy rule that applies — Rule 8-210 c) for a commercial parking structure rather than the dwelling rules of 8-200 and 8-202. The same 200 units therefore calculate at nameplate:

1,440 kVA against 1,331.2 kVA is 8.2 percent of difference created purely by the NEC floor. Where no EVEMS is installed, Ontario’s Electrical Safety Authority notes in Bulletin 86-1-6 that Table 38 demand factors are permitted for EVSE under Rules 8-202 to 8-210, which can take the Canadian figure lower still — though the Section 8 subcommittee recommended deleting Table 38 for the 2024 edition, so its availability depends on the edition in force.

The continuous rule is inverted. Rule 86-302 makes the EVSE connected load continuous for Rule 8-104, and 8-104 6) expresses the margin as a cap — continuous load not exceeding 80 percent of conductor ampacity where the device is not marked for 100 percent operation — rather than as the NEC’s 125 percent multiplier. At a 600Y/347 V service the current is 1,331,200 ÷ (√3 × 600) = 1,331,200 ÷ 1,039.23 = 1,280.9 A, so the minimum rating is 1,280.9 ÷ 0.80 = 1,601.1 A, overshooting a 1,600 A lineup by 1.1 A. Marked for 100 percent continuous operation under 8-104 5), the same 1,280.9 A fits a 1,600 A frame directly. One sentence of marking, one frame size.

The two effects are often conflated. Voltage alone accounts for the step from 1,601.2 A — what 1,331.2 kVA draws at 480 V — down to 1,280.9 A at 600 V, a 20 percent reduction worked more fully in choosing a facility distribution voltage. The rest of the gap to the American 1,732.1 A is the 220.57 floor.

The relief goes further. Rule 8-106 10) sets the EVSE demand load equal to the maximum the EVEMS allows — the NEC 625.42(A) result. Rule 8-106 11) then permits the EVSE demand load not to be considered in the calculated load at all, provided the EVEMS monitors the consumer’s service and feeders and controls the EVSE in accordance with Rule 8-500. The NEC has no equivalent. ESA Bulletin 86-1-6 distinguishes the two by metering point, with current transformers on the branch for 8-106 10) and on the service conductors for 8-106 11). The relief is not automatic: writing in IAEI Magazine, Ark Tsisserev notes that no CSA system standard yet covers a field-assembled EVEMS, so its use falls to the discretion of the local AHJ.

The marking on the overcurrent device decides the rest. Rule 8-104 5) permits a fixed-rating EVEMS rated 600 A on a 600 V feeder to carry 600 × 600 × √3 ÷ 1000 = 623.5 kVA where the device is marked for 100 percent continuous operation; where it is not, 8-104 6) holds it to 480 A, or 498.8 kVA — 124.7 kVA decided by a label.

Site reference — spaces to service to transformer

Unmanaged NEC figures at the 220.57 floor of 7,200 VA per space, on a 480Y/277 V service. Read the setpoint ladder above against it to size the relief.

The same ladder drives the service capacity calculator, and the transformer column uses the standard ANSI kVA steps carried by the transformer sizing calculator.

What to specify

• The enforced setpoint in kW and in amperes, written on the one-line so a plan reviewer can trace it, cited to NEC 625.42(A) and 750.30 or to CEC 8-500 with 8-106 10) or 11). The number comes from the energy calculation above — 400 kW for the worked garage — not from a vendor default.
• Which relief path applies in Canada, since 8-106 10) keeps the EVEMS maximum in the calculated load and 8-106 11) removes it, and the two need different metering points per ESA Bulletin 86-1-6 — the branch in one case, the service conductors in the other.
• Who holds access to the ampere-adjusting means, where the hardware-limited path of NEC 625.42(B) is used instead of a controller. 750.30(C) requires restricted access, and the adjusted value has to appear on the rating label.
• Behaviour on controller or communications failure. NEC 750.30 requires current to stop on a malfunction. Specify the tested fallback current and who witnesses the test, not the phrase “fails safe”.
• The existing-service baseline, from NEC 220.87 at 125 percent of the maximum demand over a year, or over 30 days of recorded data, or from CEC 8-106 8) using the utility’s 12-month maximum demand.
• Minimum per-port current at full simultaneity, computed as the setpoint divided by the port count and the voltage — 9.6 A on the worked site — and checked against the EVSE submittal so the controller is never asked to command below what the equipment can hold.
• Metering and sub-billing, which may call for a CT-metering distribution cabinet or a dedicated section in the distribution switchboard, sized at the managed value rather than the connected value.

Common mistakes

• Using nameplate below the NEC floor. Two hundred 6,656 VA units look like 1,331.2 kVA. NEC 220.57 makes the calculated figure 1,440 kVA — 108.8 kVA of paper load. It does not move this transformer, since both bases round to 2,000 kVA, but it moves the feeder and the paperwork, and the plan reviewer catches it at the load schedule.
• Applying a demand factor to EVSE under the NEC. There is no Article 220 demand factor for EV charging, so 200 spaces at 60 percent diversity give 864 kVA and a 1,500 kVA transformer where the code requires 2,000 kVA. Diversity is only available through 625.42(A) or (B), enforced by hardware.
• Sizing the main to the setpoint instead of 125 percent of it. A 400 kVA cap is 481.1 A, and the device must carry 601.4 A, not 481.1 A. Rounding the wrong number puts a 500 A main on a load that NEC 210.20(A) requires 700 A to carry.
• Rounding a ceiling upward. The largest setpoint that fits a 600 A device is 399.06 kVA. Rounded up to 399.1 kVA it produces 600.05 A and forces the 700 A frame; truncated to 399 kVA it does not. Limits round down.
• Reading NEC 220.87 off a utility bill. The clause requires maximum demand, over a year or over 30 days of recorded data, and is unavailable where the service has peak-load shaving. Kilowatt-hours are energy, not demand.
• Assuming the Canadian and American answers match. The same garage is 1,440 kVA in the NEC and 1,331.2 kVA in the CEC, and under CEC 8-106 11) the EVSE contribution to the calculated load can be nil — a result NEC 625.42 never produces.

Where Entogo fits

Entogo manufactures the commercial AC chargers, the low-voltage switchboards and panelboards, the distribution transformers and the battery energy storage that sit behind a managed charging site. The equipment is specified against the applicable NEC and CEC installation rules and designed and built to the applicable UL and CSA standards; UL (cULus)/CSA certifiable on request. Because the Level 2 chargers, the dual-socket units and the rest of the EV charging line are produced in the same vertically integrated factory, the managed setpoint, the switchboard rating and the transformer kVA are specified against one another rather than across separate supply chains.

Scalable in-house capacity and engineering support sit behind that, and every product carries a minimum 36-month warranty with a one-business-day service response. Teams can run their own numbers in the EV charging service capacity calculator, price the upstream unit through transformer quote, and see the wider package under EV charging infrastructure. Where the peak cannot be managed down far enough, pairing the site with commercial and industrial storage shaves the grid draw the service has to support.

Load management converts an EV buildout from a service-capacity problem into a controls problem, and on the worked site the conversion is worth a factor of four on the transformer. The saving is only real when the setpoint is derived from the energy the site must deliver, enforced by equipment specified against the applicable product standard, and written into the drawings with the clause beside it — because the number on the one-line is what the utility, the plan reviewer and the inspector will each size their own decision against.