Circuit Breaker Size Calculator

A Circuit Breaker Size Calculator is a tool used to determine the correct size of a circuit breaker needed for a specific electrical circuit. The right size of circuit breaker is crucial for safety, as it helps prevent overloads or short circuits that could lead to electrical fires or equipment damage. By calculating the required breaker size, the tool ensures that the circuit is protected from excessive current while maintaining efficient power distribution.

The calculator works by using formulas based on the type of circuit (DC, single-phase AC, or three-phase AC), the power of the load, and the voltage of the system. It is widely used in both residential and commercial electrical installations, ensuring that each circuit operates safely and within capacity.

Formula of Circuit Breaker Size Calculator

The formula for calculating the size of a circuit breaker depends on the type of circuit. Below are the formulas for each type:

1. DC Circuit (Direct Current)

For a DC Circuit, the formula to calculate the current rating (I) of the circuit breaker is:

I(C.B) = P / V

Where:

• I(C.B) = Current rating of the circuit breaker (in Amps)
• P = Power of the load (in Watts)
• V = Voltage of the circuit (in Volts)

2. Single-Phase AC Circuit

For a Single-Phase AC Circuit, the formula is:

I(C.B) = P / (V * PF)

Where:

• I(C.B) = Current rating of the circuit breaker (in Amps)
• P = Power of the load (in Watts)
• V = Voltage of the circuit (in Volts)
• PF = Power factor of the load (unitless)

3. Three-Phase AC Circuit

For a Three-Phase AC Circuit, the formula is:

I(C.B) = P / (√3 * V * PF)

Where:

• I(C.B) = Current rating of the circuit breaker (in Amps)
• P = Power of the load (in Watts)
• V = Voltage of the circuit (in Volts)
• PF = Power factor of the load (unitless)
• √3 = Square root of 3 (approximately 1.732)

Additional Considerations:

• Safety Factor: It’s recommended to add a safety factor to the calculated current to account for fluctuations or potential future increases in load. A common safety factor is 25%. This means the current rating should be increased by 25% above the calculated value.
• Continuous vs. Non-Continuous Loads: If a circuit has both continuous and non-continuous loads, the total load current should be calculated as follows:Total Load Current = 1.25 * Continuous Load Current + Non-Continuous Load Current
• Circuit Breaker Ratings: The circuit breaker chosen should have a rating slightly higher than the calculated current. For example, if the calculated current is 12.4 Amps, a 15 Amp breaker would typically be chosen for safety and reliability.

Table for General Terms

The table below provides general terms and conversions commonly searched for in circuit breaker sizing. It can be helpful to reference these terms for quick conversions or calculations:

Term	Description
Power (P)	Measured in Watts; the total power consumption of the load.
Voltage (V)	Measured in Volts; the electrical potential difference.
Current (I)	Measured in Amps; the flow of electric charge.
Power Factor (PF)	A unitless number between 0 and 1 that accounts for the phase difference in AC circuits.
Safety Factor (SF)	A recommended multiplier (typically 1.25) to ensure the circuit breaker is appropriately rated.
Continuous Load	A load that runs for 3 or more hours consecutively.
Non-Continuous Load	A load that operates intermittently or less than 3 hours.

Example of Circuit Breaker Size Calculator

Let’s say you need to calculate the circuit breaker size for a single-phase AC circuit. The load has the following parameters:

• Power (P) = 3000 Watts
• Voltage (V) = 240 Volts
• Power Factor (PF) = 0.9

Using the formula for a single-phase AC circuit:

I(C.B) = 3000 / (240 * 0.9)

I(C.B) = 3000 / 216 = 13.89 Amps

Thus, the required current rating for the circuit breaker is approximately 13.89 Amps. Applying a safety factor of 1.25:

13.89 * 1.25 = 17.36 Amps

In this case, you would select a 20 Amp circuit breaker to ensure safety and proper protection.

Most Common FAQs