EV Load Management
Biggest EV charger on a 150 amp service
The largest EV charger a 150A 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 | 150A (36,000 VA at 240V) |
| Example measured peak | 80A |
| 125% of the peak (NEC 220.87) | 100A |
| Headroom before the charger | 50A |
| Biggest charger (headroom at 100%, floored) | 48A |
| Branch (125% continuous) | #6 Cu / 60A / #10 ground |
With a Load-Management Device
A listed load-management device relaxes the service calculation (NEC 220.70 / 625.42(A) / 750.30), so the 80A peak stops being the binding limit. A shed device (a DCC) on a 60A EV pass-through breaker enables a 48A charger on a #6 Cu / 60A 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 150 amp service for an EV charger?
By NEC 220.87 you take 125% of your measured peak demand and subtract it from the 150A service. For an example 80A peak that leaves 50A 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. So the biggest charger the headroom allows is 48A (floored to a standard size) on #6 Cu / 60A, the branch sized at 125% of the charger (NEC 625.41). Your own metered demand governs; enter it in the calculator.
Can I install a 48A EV charger on a 150 amp service?
Yes, at the example 80A peak this 150A service takes up to a 48A charger, so a 48A unit fits on #6 Cu with a 60A breaker (NEC 625.41). Confirm against your own measured demand.
Does a load-management device avoid a service upgrade on a 150 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 60A EV breaker enables a 48A charger on this service regardless of the 80A peak, because it disconnects the charger when the panel nears its limit. The branch stays at 125% of the full charger output (#6 Cu / 60A here); the device relaxes the service calculation, never the branch.
Use Your Own Metered Demand
The 80A 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.