Circuit Breaker Calculator

Determine the proper circuit breaker size for electrical circuits using this calculator. Proper breaker sizing ensures safety and prevents electrical hazards.

How to Use This Calculator

To calculate the proper circuit breaker size:

Enter the total load current in amperes (A)
Select the voltage level (120V or 240V)
Choose the conductor type (copper or aluminum)
Click "Calculate" to determine the recommended breaker size

The calculator will display the recommended breaker size based on the National Electrical Code (NEC) standards. Always consult a licensed electrician for critical installations.

Formula Used

The recommended circuit breaker size is determined by the following factors:

Breaker Size = (Load Current × 125%) + (Voltage Drop Factor) + (Conductor Type Adjustment)

The 125% factor accounts for future load growth. The voltage drop factor ensures proper voltage at the far end of the circuit. The conductor type adjustment accounts for different resistance characteristics between copper and aluminum.

Worked Example

Let's calculate the proper breaker size for a 20A load at 120V using copper conductors:

Load current = 20A
Voltage = 120V
Conductor type = Copper

Using the formula:

Breaker Size = (20 × 1.25) + (1.5) + (0) = 25 + 1.5 + 0 = 26.5A

The recommended breaker size is 25A (standard breaker sizes are typically in 5A increments).

Frequently Asked Questions

Why is the breaker size larger than the load current?

The breaker size is larger than the load current to account for future load growth and ensure proper voltage at the far end of the circuit.

What happens if I use a breaker that's too small?

A breaker that's too small will trip frequently, potentially causing inconvenience and safety hazards. It may also indicate a wiring or equipment problem.

Can I use this calculator for commercial installations?

This calculator provides general guidance. Always consult a licensed electrician for commercial installations as they have specific requirements.