EV Load Management
EV charger with vs without load management
The same service, both ways: the biggest EV charger by NEC 220.87 alone, and what a listed load-management device unlocks. The device relaxes the service calculation without a panel upgrade; the branch is always sized to the full charger output.
The Same Service, Both Ways
| Service (example peak) | No device (220.87) | Shed (DCC) | Throttle (48A EVSE) | Circuit-share (30A branch) |
|---|---|---|---|---|
| 100A (60A peak) | none | 40A | 0A delivered | 24A |
| 125A (70A peak) | 32A | 48A | 37.5A delivered | 24A |
| 150A (80A peak) | 48A | 48A | 48A delivered | 24A |
| 200A (90A peak) | 48A | 48A | 48A delivered | 24A |
The shed column is a DCC on the largest EV breaker the sourced service-compatibility matrix permits at each service size, independent of the peak. The throttle column is a full 48A EVSE whose delivered current is the service headroom. The circuit-share column is a Splitvolt on a 30A dryer branch (24A, one appliance at a time). Branches at the 100A service: shed 40A charger on #8 / 50A, throttle 48A hardware on #6 / 60A, circuit-share 24A on the existing #10 / 30A. For the circuit-share case, the existing shared branch (the 30A dryer circuit) must already be code-compliant for its own breaker (a 30A branch on #10 Cu) before a Splitvolt reuses it; confirm the host circuit with your electrician and the AHJ.
What the Device Changes, and What It Never Changes
A listed EVEMS changes ONE thing: the SERVICE load calculation. NEC 220.70 lets an EMS-controlled maximum be used as a single value in the feeder or service calc, 625.42(A) relaxes the service and feeder for a listed EMS in accordance with 750.30, and 750.30 requires the EMS to keep the load within conductor ampacity. What it never changes is the BRANCH circuit: the conductor and breaker are always sized to 125% of the full EVSE hardware output (NEC 210.20(A) / 625.41). The EVSE's own restricted-access adjusted setting under NEC 625.42(B) is a different question, never an external device, and this calculator will not apply one. The one route the NEC gives for a smaller branch is the EVSE's own restricted-access adjusted setting under NEC 625.42(B), and it is a route a calculator cannot take for you: the conditions it attaches, under 750.30(C) and the manufacturer's instructions, are facts about installed equipment. The 4 this tool can name are not a full compliance checklist. Size from the full rating unless a qualified person has verified them, and 625.42(B) itself, on site.
Frequently Asked Questions
Does a load-management device let me avoid a service upgrade?
Often, yes. NEC 220.70 and 625.42(A) permit a listed energy management system to relax the SERVICE load calculation in accordance with 750.30, so a charger that would not fit by 220.87 alone can be installed without enlarging the service. On an example 100A service at a 60A peak, the biggest charger by 220.87 alone is none at all; a shed device (a DCC on a 50A EV breaker) raises that to 40A. The device relaxes the service calculation, never the branch circuit.
Why does the branch stay the same size with a device?
Because an external device does not change the charger's rating. NEC 625.42(A) reaches the service and feeder load calculation; the branch conductor and breaker are always sized to 125% of the full EVSE hardware output (NEC 210.20(A) / 625.41). If the device fails or is bypassed the EVSE can pull its full current, so the conductor must always carry it. The one route the NEC gives for a smaller branch is the EVSE's own restricted-access adjusted setting under NEC 625.42(B), and it is a route a calculator cannot take for you: the conditions it attaches, under 750.30(C) and the manufacturer's instructions, are facts about installed equipment. The 4 this tool can name are not a full compliance checklist. Size from the full rating unless a qualified person has verified them, and 625.42(B) itself, on site.
Which device type raises the charger the most?
A shed device (DCC) gives the largest fixed charger because it disconnects the EVSE and bounds it only by 80% of its own breaker, independent of the service headroom. A throttle device (Emporia, Wallbox Power Boost) keeps a full-size EVSE but caps the delivered current to the headroom, so on a tight service it delivers less. A circuit-share switch (Splitvolt) reuses one existing branch for a 24A charger, one appliance at a time. An interlock guarantees the car and the appliance never draw at once, so the two are a noncoincident load under NEC 220.60, which permits counting only the largest of them. This tool does not ask which appliance is on the shared branch, so it does not know which is larger and does not compute that netting: the charger stays in the service calculation at its full NEC 220.57 value, which is the conservative end.
Compute Your Own
Enter your service and measured demand for the base NEC 220.87 answer; the device pages show what each device type unlocks on top of it.
Go Deeper
EV Load Management Hub
The interactive inverse solve and all three device types.
Max Charger Chart
Every service size across measured-demand levels, one table.
DCC (Shed Device)
The charger a DCC allows, by breaker size, and the minimum-main matrix.
Load Calculator (NEC 220)
The forward direction: 220.82 sizing and the 220.87 existing-load check.