NEC Compliant

Breaker Rating Selector

Calculate the correct circuit breaker size for solar PV systems, EV chargers, and continuous loads using the NEC 125% rule.

⚡ Load Parameters

125%

NEC requires 125% for loads running 3+ hours continuously.

Recommended Breaker

-- A

Standard size, NEC 240.6

Calculated Current -- A
Design Current (125%) -- A
Wire Gauge (Cu) --
Wire Gauge (Al) --
Pole Count --

⚠️ This tool provides general guidance per NEC. Always consult a licensed electrician and verify local codes, derating factors, ambient temperature, and conduit fill requirements before installation.

How Breaker Sizing Works

A quick reference for solar PV and EV charger installations.

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Step 1: Calculate Current

I = P ÷ (V × PF) for single-phase, or I = P ÷ (V × √3 × PF) for three-phase systems.

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Step 2: Apply 125% Rule

NEC 210.20(A) & 215.3 require 125% sizing for continuous loads running 3+ hours (solar, EV).

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Step 3: Round Up

Select the next standard breaker size per NEC 240.6(A). Match wire ampacity per NEC 310.16.

Frequently Asked Questions

What size circuit breaker do I need for a 10kW solar system?

For a 10kW solar system at 240V single-phase, the output current is approximately 41.67A. Applying the NEC 125% continuous load factor gives 52.08A, so you need a 60A double-pole breaker. For 208V systems, use an 80A breaker. Always verify wire gauge and local code requirements with a licensed electrician.

How to calculate breaker size for EV charger?

EV chargers are continuous loads under NEC, so breaker size equals charger current multiplied by 1.25. A 48A Level 2 EV charger requires a 60A breaker (48 × 1.25 = 60A). A 32A charger needs a 40A breaker. Use #6 AWG copper wire for 60A circuits at typical residential distances under 50 feet.

Why do solar and EV loads need 125% breaker sizing?

NEC Article 210.20 and 215.3 require overcurrent devices for continuous loads (running 3+ hours) to be sized at 125% of the load current. Solar inverters and EV chargers often run continuously, so the 125% rule prevents nuisance tripping, reduces heat buildup, and ensures long-term safety of the installation.