TryBuildCalcLevel 2 EV Charger Wire Size Calculator (240V Home Charging Circuit)
Calculate your Level 2 charger wire size.
🕒 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: 40A breaker, 8 AWG copper
For a 32.0A (7.7 kW) charger at 240V — sized by ampacity, not voltage drop
Ampacity Check
Design current: 40.0 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: 32.0 A
Minimum size by voltage drop: 12 AWG
Allowed drop: 3.0%
Final wire's actual drop: 0.83% (2.00 V)
Circuit Summary
| System | 240 V, single-phase |
| One-way run length | 40.0 ft (12.2 m) |
| Connection / location | Hardwired, indoor |
Panel Impact (Informational)
| Service Size | % of Service Used by This Circuit |
|---|---|
| 100A | 40.0% |
| 125A | 32.0% |
| 150A | 26.7% |
| 200A | 20.0% |
| 225A | 17.8% |
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.
Level 2 charger wire sizing
Level 2 charging (240V) is the standard choice for a dedicated home EV charging setup — this page is pre-set to a common 32A charger, a practical choice for most daily driving.
Edit the charger amperage above to match your actual EVSE — common Level 2 ratings are 16A, 24A, 32A, 40A, and 48A.
- A 32A charger needs a 40A circuit (32 × 1.25), commonly 8 AWG copper on a typical run.
- Higher-amperage chargers need proportionally larger wire and breakers — check your actual charger's rating.
- Run length matters — a longer run may need a larger wire size than ampacity alone would suggest, due to voltage drop.
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 | 32.0A at 240V (7.7 kW) | Sets the base current before the continuous-load factor |
| Run Length | 40.0 ft | Sets the voltage drop check |
| Connection / Location | Hardwired, indoor | Sets the GFCI requirement |
Step 1 — Design Current
| Calculation | 32.0 × 1.25 |
| Design current | 40.0 A |
Steps 2-3 — Wire and Breaker Size
| Check | Result |
|---|---|
| Minimum size by ampacity (40.0A design current) | 8 AWG |
| Minimum size by voltage drop (3.0% max) | 12 AWG |
| Final wire (larger of the two) | 8 AWG |
| Breaker (design current rounded to standard size) | 40 A |
Therefore, for a 32.0A charger at 240V, you need 40A 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.