Why does the EV circuit need to be 125% of the charger's current?

An EV charger runs at full current for three hours or more, which the NEC defines as a continuous load. NEC 625.17 and 210.20(A) require the branch circuit and overcurrent device to be sized at 125% of that continuous current so the breaker and wire never run at their absolute limit.

What size breaker do I need for a 48 A charger?

A 48 A continuous charger needs 48 multiplied by 1.25, which equals 60 A. The next standard breaker at or above 60 A is a 60 A breaker, paired with a 6 AWG copper conductor. Always confirm against the charger's installation manual.

Can I use the charger's kW rating instead of amps?

Yes. Switch to kW mode and the tool converts power to current using amps equals watts divided by volts. An 11.5 kW charger at 240 V draws about 48 A, which is then sized up by 125% just like a nameplate-amp entry.

Does this size the wire for voltage drop and temperature?

The conductor recommendation uses the copper 75°C ampacity column of NEC Table 310.16 for up to three current-carrying conductors at normal ambient. For long runs add a voltage-drop check, and apply temperature and conduit-fill derating before finalizing.

Is the grounding conductor included?

Yes. The equipment grounding conductor is selected from NEC Table 250.122 based on the breaker rating, since the EGC is sized by the overcurrent device protecting the circuit, not by the phase conductor.

EV Charger Load & Wiring Calculator

EV chargers are a continuous load, so the National Electrical Code requires their circuits to be sized larger than the charger’s running current. This calculator applies the NEC 625.17 / 210.20(A) 125% rule and returns the breaker, copper conductor, and grounding conductor for a code-compliant Level 1, Level 2, or commercial EV charging installation.

How it works

The charger nameplate current is treated as a continuous load and multiplied by the 125% continuous-load factor:

design current = nameplate amps × 1.25
breaker (OCPD) = next standard breaker ≥ design current
conductor      = smallest 75°C copper wire with ampacity ≥ design current
EGC            = NEC Table 250.122 size for the chosen breaker

If you enter the charger by power instead of current, the tool first converts using amps = watts / volts (single-phase), then applies the same 125% rule. Standard breaker ratings come from NEC 240.6(A) and conductor ampacities from the copper 75°C column of Table 310.16.

Example and tips

A common 48 A Level 2 home charger on a 240 V circuit needs 48 × 1.25 = 60 A, which calls for a 60 A breaker and 6 AWG copper conductor with a 10 AWG ground. A 40 A charger drops to a 50 A breaker on 8 AWG copper. Keep these points in mind: the 125% rule applies to the breaker and the wire; many hardwired chargers let you set a lower current limit in software, which can reduce the circuit you need; and for long runs from the panel, always add a voltage-drop check on top of the ampacity result.