Breaker Size Calculator

Breaker size calculator is a online calculator tool (electrical calculator) that may be used to determine the proper size of a circuit breaker for a certain electrical circuit.

It takes into consideration a wide range of requirements such as voltage, power consumed by appliances/devices connected to the circuit, wire type, and safety regulations.

Several standards, including BS 7671 and the National Electrical Code (NEC), specify “Ampacity” for different types of materials.

When a circuit overload or fault occurs, a circuit breaker used to protects the electrical appliances.

When the breaker trips, devices linked to the same circuit are cut off from the more current, causing them to lose power.

How do I calculate breaker size?

In general, a breaker should be sized to withstand 125% of the load (or 25% more capacity) and no less.

Oversized breakers might cause wires to overheat without interrupting the current flow. Undersized breakers, on the other end, may trip continuously under normal operation.

A circuit breaker has a rating in amperes (A), which tells us how much electricity may safely pass through the breaker before it trips. A 10 A breaker, for example, enables for up to 10 A of total load to be interconnected at the same time.

The desired breaker for electrical system equipment is chosen by a calculation known as breaker sizing.

Formula to determine Breaker Size

If we understand the wattage of every appliance in the circuit, we may use different formulae based on the kind of current to calculate their relative loads.

Load in DC Supply

I = W/V

Where,

I – Current in Amps (A)

W – Load Connected in Watts (W)

V – Voltage in Volts (V)

Load in AC Single Phase Supply

I = W/(V x P.F)

Where,

I – Current in Amps (A)

W – Load Connected in Watts (W)

V – Voltage in Volts (V)

P.F – Power Factor

Load in AC Three Phase Supply

I = W/(V x P.F x √3)

Where,

I – Current in Amps (A)

W – Load Connected in Watts (W)

V – Voltage in Volts (V)

P.F – Power Factor

What is Safety Factor (S.F)?

A specific overload condition can be operated for a specific period of time on some equipment. When sizing breakers, overload conditions are taken into consideration for increased protection. A safety factor is the 25% increase in current over the rated current, such as in the case of a motor that has a 100 A rating but can operate at 125 A for an hour.

The safety factor of common loads are listed below (Choose based on the connected load):

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