EV Load Management
Biggest EV charger on a 125 amp service
The largest EV charger a 125A 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 | 125A (30,000 VA at 240V) |
| Example measured peak | 70A |
| 125% of the peak (NEC 220.87) | 87.5A |
| Headroom before the charger | 37.5A |
| Biggest charger (headroom / 1.25, floored) | 24A |
| Branch (125% continuous) | #10 Cu / 30A / #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 70A peak stops being the binding limit. A shed device (a DCC) on a 40A EV pass-through breaker enables a 32A charger on a #8 Cu / 40A 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 | 16A | #12 Cu / 20A |
| 125A service | 70A | 24A | #10 Cu / 30A |
| 150A service | 80A | 40A | #8 Cu / 50A |
| 200A service | 90A | 48A | #6 Cu / 60A |
Frequently Asked Questions
How many amps can I add to a 125 amp service for an EV charger?
By NEC 220.87 you take 125% of your measured peak demand and subtract it from the 125A service. For an example 70A peak that leaves 37.5A of headroom, and because EV charging is continuous (NEC 625.42) you divide by 1.25, so the biggest charger is 24A on #10 Cu with a 30A breaker. Your own metered demand governs; enter it in the calculator.
Can I install a 48A EV charger on a 125 amp service?
Not by NEC 220.87 alone at the example 70A peak: this 125A service tops out at a 24A charger. A listed load-management device can allow a larger one (a shed device on a 50A EV breaker enables a 40A charger, which the DCC matrix permits on a service of 100A or larger), but the branch is still sized to the full charger output.
Does a load-management device avoid a service upgrade on a 125 amp service?
Often, yes, for the right device. 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 40A EV breaker enables a 32A charger on this service regardless of the 70A peak, because it disconnects the charger when the panel nears its limit. The branch stays at 125% of the full charger output (#8 Cu / 40A here); the device relaxes the service calculation, never the branch.
Use Your Own Metered Demand
The 70A 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.