Breaker Size Calculator & Breaker Size Chart

Breaker size calculator

This calculator is the hybrid version of 3 phase breaker size calculator & single phase breaker calculator. later in this post, we will give you the breaker size chart too. Stay tuned.

Electricity is one of the most important things in our daily lives. One of the vital components in electricity is the MCB (Miniature Circuit Breaker).

Get to know the MCB

MCB stands for Miniature Circuit Breaker. It is an automatic electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. MCB 1 phase has 1 toggle switch, MCB 3 phase have 3 toggle switches. These toggle switch only have 2 positions, on and off.

Some of engpocket friends must be asking yourself, “why don’t we use fuse?”. MCB is different with fuse, which operates once and must be replaced, MCB can be reset. We just have to flip the toggle switch from the OFF position back to ON position after the MCB trips.

MCB single phase vs MCB 3 phase. Spot the difference

Breaker size formula

Do you want to know how the breaker size formula worked?
Pay attention to below formula, based on the breaker size calculator:

Case 1: Input is in Volt-Amperes (VA)

This is apparent power, so we don’t use the Cos φ.

• Single-phase (220V):

$$I=\frac{P_{\text{VA}}}{220}$$I=220PVA​​

• Three-phase (380V line-to-line):

$$I=\frac{P_{\text{VA}}}{\sqrt{3}\times 380}\approx \frac{P_{\text{VA}}}{658}$$I=3​×380PVA​​≈658PVA​​

Case 2: Input is in Watts (W)

This requires power factor (Cos φ) to convert to apparent power first:

• Single-phase:

$$I=\frac{P_{\text{W}}}{220\times \text{PF}}$$I=220×PFPW​​

• Three-phase:

$$I=\frac{P_{\text{W}}}{\sqrt{3}\times 380\times \text{PF}}\approx \frac{P_{\text{W}}}{658\times \text{PF}}$$I=3​×380×PFPW​​≈658×PFPW​​

Case examples

1 phase case

An engpocket electrician is upgrading a kitchen. A new induction cooker hood (3.5 kW) and oven (2.5 kW) are being installed on the same circuit.

• Total load = 3500 W + 2500 W = 6000 W
• 1-phase, 220V in standard residential
• Estimated power factor ≈ 0.95 (modern appliances)

$$I=\frac{6000}{220\times 0.95}\approx 28.7\text{ A}$$

Standard breakers come in steps (25A, 32A…), so he can’t use a 25A, it would trip. So, he should install a 32A MCB 1 Phase

3 phase case

Rocky manages a small auto repair shop. A new 3 phase air compressor (7.5 kW motor) is delivered into his place. The nameplate says: 380V, 3 phase, 15 A full-load current.
Even though the motor says it is 15 A, he could not install a 16A breaker. Why?

• Motors have inrush current (5–7× running current at startup).
• Standards (like IEC 60947) require MCB with higher tolerance (often Type C or D magnetic trip).

So, he must select:

A 25A 3-pole MCB (Type C)

Breaker size chart

As a compliment of the breaker size calculator, here we provide you the breaker size chart too

If engpocket friends wanted to use BTU to PK calculator to calculate the and decided air conditioner capacity, you can visit this post link.