EV Load Management
Biggest EV charger on a 100 amp service
The largest EV charger a 100A service can take by the NEC 220.87 method, worked at an example measured peak, plus what a load-management device unlocks. Your own metered demand is the real input; use the calculator for your number.
The Math (NEC 220.87)
| Service rating | 100A (24,000 VA at 240V) |
| Example measured peak | 60A |
| 125% of the peak (NEC 220.87) | 75A |
| Headroom before the charger | 25A |
| Biggest charger (headroom at 100%, floored) | none |
| Branch (125% continuous) | no branch circuit: NEC 220.87 alone fits no charger here |
With a Load-Management Device
A listed load-management device relaxes the service calculation (NEC 220.70 / 625.42(A) / 750.30), so the 60A peak stops being the binding limit. A shed device (a DCC) on a 50A EV pass-through breaker enables a 40A charger on a #8 Cu / 50A branch. A throttle device (Emporia, Wallbox Power Boost) runs a full 48A EVSE and modulates the delivered current to your headroom. In every case the branch is sized to the full charger output; the device never shrinks the conductor.
Compare side by side: with vs without load management. Device details: DCC, Emporia, Wallbox Power Boost, Splitvolt.
Other Service Sizes
| Service | Example peak | Biggest charger | Branch |
|---|---|---|---|
| 100A service | 60A | none | no branch circuit: NEC 220.87 alone fits no charger here |
| 125A service | 70A | 32A | #8 Cu / 40A |
| 150A service | 80A | 48A | #6 Cu / 60A |
| 200A service | 90A | 48A | #6 Cu / 60A |
Frequently Asked Questions
How many amps can I add to a 100 amp service for an EV charger?
By NEC 220.87 you take 125% of your measured peak demand and subtract it from the 100A service. For an example 60A peak that leaves 25A of headroom, and the charger enters the 220.87 service check at 100% of its NEC 220.57 value, which is 7,200 VA or the nameplate rating, whichever is larger. That headroom is under the 7,200 VA any EVSE is calculated at, so NEC 220.87 adds no charger to this service on its own and a listed load-management device is the route. Your own metered demand governs; enter it in the calculator.
Can I install a 48A EV charger on a 100 amp service?
Not by NEC 220.87 alone at the example 60A peak: this 100A service cannot take any charger at all. A listed load-management device can allow a larger one (a shed device on a 50A EV breaker enables a 40A charger, which the sourced DCC service-compatibility matrix permits on this service), but the branch is still sized to the full charger output.
Does a load-management device avoid a service upgrade on a 100 amp service?
For the right device, yes. NEC 220.70 and 625.42(A) let a listed EMS relax the service load calculation in accordance with 750.30. A shed device (DCC) on a 50A EV breaker enables a 40A charger on this service regardless of the 60A peak, because it disconnects the charger when the panel nears its limit. The branch stays at 125% of the full charger output (#8 Cu / 50A here); the device relaxes the service calculation, never the branch.
Use Your Own Metered Demand
The 60A peak above is an example. Enter your service and your actual measured peak for the real answer.
Related Tools
EV Load Management Hub
The inverse 220.87 solve and all three device types.
Load Calculator (NEC 220)
The forward direction: 220.82 sizing and the 220.87 existing-load check.
EV Charger Calculator
Wire, breaker, and panel capacity for a Level 2 charger per NEC Article 625.
Wire Size Calculator
The correct conductor per NEC 310.16 with the 110.14(C) terminal cap.