TryBuildCalcEV Charger Panel Capacity Calculator (Circuit Impact on Your Service)
Check your EV charger's panel impact.
🕒 Last updated: August 29, 2026
Inputs
ℹ️Select your EVSE's charging level and amperage, or choose Custom to enter it directly.
ℹ️The EVSE's own nameplate rated continuous current — not the vehicle's onboard charger rating.
ℹ️Distance from the panel/breaker to the EVSE, one way — not round trip.
ℹ️The wire's own insulation rating (check the product's markings, e.g. THHN, THWN-2).
ℹ️Per NEC 110.14(C) — the breaker/panel/EVSE's own temperature rating. The calculator uses the lower of this and the insulation rating above.
Connection & Location
ℹ️Affects GFCI protection requirements per NEC 625.54.
Advanced (NEC Derating)
Cost
Recommended Circuit: 50A breaker, 8 AWG copper
For a 40.0A (9.6 kW) charger at 240V — sized by ampacity, not voltage drop
Ampacity Check
Design current: 50.0 A (125% continuous factor, NEC 625.41)
Minimum size by ampacity: 8 AWG
Derating factor applied: 1.00×
Final wire's derated ampacity: 50.0 A
Voltage Drop Check
Charger rated current: 40.0 A
Minimum size by voltage drop: 10 AWG
Allowed drop: 3.0%
Final wire's actual drop: 1.30% (3.13 V)
Circuit Summary
| System | 240 V, single-phase |
| One-way run length | 50.0 ft (15.2 m) |
| Connection / location | Hardwired, indoor |
Panel Impact (Informational)
| Service Size | % of Service Used by This Circuit |
|---|---|
| 100A | 50.0% |
| 125A | 40.0% |
| 150A | 33.3% |
| 200A | 25.0% |
| 225A | 22.2% |
This is a single circuit's share of a service, not a full load calculation — use the Panel Size Calculator to check your service has capacity for this plus everything else.
Assumptions Used
NEC 625.41 (125% continuous-load factor), NEC Table 310.16 ampacity, NEC 110.14(C) governing rating, NEC 240.4(D) small-conductor cap. Assumes a dedicated branch circuit (NEC 625.42) — not a shared/EMS-managed circuit. This is a reference estimate — confirm with a licensed electrician before installation.
Checking your panel has enough total capacity for this plus everything else? Panel Size Calculator →
Need to size the conduit for this and other conductors? Conduit Fill Calculator →
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete EV Charger Load Calculator.
EV charger panel capacity impact
Before installing an EV charger, it's worth checking roughly how much of your panel's capacity the new circuit will use — this page is pre-set to a common 40A charger scenario.
The Panel Impact table shows this circuit's percentage across common service sizes; for a full picture including your existing loads, use the Electrical Load / Panel Size Calculator.
- A 40A charger needs a 50A breaker — roughly 25% of a 200A service, or 50% of a 100A service, just for this one circuit.
- This is informational only — it doesn't account for your home's other existing loads.
- If your panel is tight on capacity, a load management system can be an alternative to a full panel upgrade.
EV Charger Circuit Formula: How Is It Calculated?
NEC 625.41's continuous-load treatment drives both the wire and breaker sizing.
Step 1 — Design Current
Design Current = Charger Rated Current × 1.25
Per NEC 625.41, EV charging equipment is always treated as a continuous load — this 125% factor applies regardless of how the charger is actually used.
Step 2 — Wire Size
Smallest AWG where: Derated Ampacity ≥ Design Current, AND
Voltage Drop at Charger Current ≤ Max Allowed %
The wire must satisfy both the design-current ampacity requirement and the voltage drop limit over the actual run length — whichever requires the larger wire governs.
Step 3 — Breaker Size
Recommended Breaker = smallest standard size ≥ Design Current
(capped by the wire's small-conductor OCPD limit, if lower)
Rounded up to a real NEC 240.6(A) standard breaker size, never a custom in-between value.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Charger | 40.0A at 240V (9.6 kW) | Sets the base current before the continuous-load factor |
| Run Length | 50.0 ft | Sets the voltage drop check |
| Connection / Location | Hardwired, indoor | Sets the GFCI requirement |
Step 1 — Design Current
| Calculation | 40.0 × 1.25 |
| Design current | 50.0 A |
Steps 2-3 — Wire and Breaker Size
| Check | Result |
|---|---|
| Minimum size by ampacity (50.0A design current) | 8 AWG |
| Minimum size by voltage drop (3.0% max) | 10 AWG |
| Final wire (larger of the two) | 8 AWG |
| Breaker (design current rounded to standard size) | 50 A |
Therefore, for a 40.0A charger at 240V, you need 50A breaker, 8 AWG copper.
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Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.