Do you need a panel upgrade for your EV charger?
This runs the NEC 220.87 existing-dwelling calculation — maximum demand over the previous 12 months, times 125%, against your service rating. It is the biggest single swing in the cost of the job: $300 for a load-management device, or $1,500–$4,000 for a service upgrade.
Where an energy management system per 750.30 provides load management, the maximum load on the service is the maximum the EMS permits — not the charger’s nameplate. Ask your electrician to price both options before committing.
Equipment over 60 A, or over 150 V to ground, needs a readily accessible, lockable disconnect.
GFCI protection is required for receptacles serving EVSE. Standard GFCI will not work for bidirectional or vehicle-to-home setups.
The four outcomes, and what each one costs
| Outcome | What it means | Added cost |
|---|---|---|
| FITS | No panel upgrade needed. Nothing beyond the circuit itself. | $0 |
| FITS AT REDUCED AMPS | Throttle the charger. No upgrade needed. A setting change, plus a durable label showing the adjusted rating. Offered down to 16 A — below that an EMS is the better buy. | $0 |
| EVEMS VIABLE | A load management device (~$300) avoids a $1,500–$4,000 panel upgrade. A load management device, plus the electrician time to commission it. | $250 – $400 |
| SERVICE UPGRADE LIKELY | Budget $1,500–$4,000 for a service upgrade. A sub-panel at $500–$1,500 sometimes covers it instead. Ask. | $1,500 – $4,000 |
Why a 48 A charger eats 60 A of your panel
EVSE is a continuous load. NEC 625.42 requires the circuit to be sized at 125% of the charger’s continuous rating. That is not a safety margin you can spend — it is the number the panel has to carry.
| Charging amps | Required circuit |
|---|---|
| 32 A | 40 A |
| 40 A | 50 A |
| 48 A | 60 A |
| 50 A | 70 A |
| 64 A | 80 A |
| 80 A | 100 A |
A 48 A charger therefore consumes 60 A of panel capacity, which is why 100 A services so often fail this test. It is also why the adjustable current setting permitted by NEC 625.42(B) is worth more than the price difference between an adjustable unit and a fixed one.
How NEC 220.87 works
For an existing dwelling you do not need a full Article 220 Part III calculation. NEC 220.87 lets you take the maximum demand over the previous 12 months from your utility’s interval data, multiply by 125%, and subtract that from the service rating. What is left is your headroom.
peakDemandAmps = (peakDemandKW × 1000) ÷ 240 requiredExisting = peakDemandAmps × 1.25 headroomAmps = serviceRatingAmps − requiredExisting chargerDemand = chargerAmps × 1.25 fits = headroomAmps ≥ chargerDemand
Most utilities will give you the 12-month peak from your account portal. If yours exports Green Button XML or an interval CSV, this page will read it in your browser and pull the peak out for you. Nothing is uploaded — there is no server to upload it to.
If you cannot get the data at all, the estimate mode applies NEC 220.12 general lighting at 3 VA per square foot, the 220.52 small-appliance and laundry allowance, and nameplate figures for the large loads you tick, then applies a coincidence factor. It is labelled an estimate everywhere it appears, because that is what it is.