How to Determine the Ampere Size of the MCB Installed at Home

Miniature Circuit Breaker (MCB) is an important device in electrical installations that functions to protect circuits from damage due to overcurrent or short circuit. Selection of the right MCB size is very important to ensure the safety and efficiency of the electrical system.

Find out how to determine the amperage of an MCB with easy-to-understand steps in this article.

Why does MCB Size Matter?

Choosing the right MCB size for your electrical system is critical to ensure optimal protection of electrical circuits. Damage to electronic equipment due to electrical interference and the risk of fire can be reduced by determining the appropriate MCB size.

MCBs have a current capacity that indicates the maximum amount of current they can handle without accidentally breaking the circuit. The selection of the MCB current capacity should be based on the current requirements of the equipment connected to the circuit. If the current passing through the MCB exceeds the specified capacity, then the MCB will automatically disconnect the circuit.

Therefore, it is important to select an MCB with a current rating higher than the current required by the equipment to be protected.

Steps to Determine the Ampere Amount of MCB

You can follow these few steps in determining the amperage of the MCB.

1. Calculating the total load power

The first step is to calculate the total power (watts) to be protected by the MCB. The trick is to add up the power of all electrical devices connected to the circuit. For example, if the circuit has a 100-watt lamp, a 75-watt fan, and a 200-watt TV, then the total power is:

Total Power = 100 watts + 75 watts + 200 watts = 375 watts

2. Convert power to current

After getting the total power, the next step is to convert the power into current (amperes). This can be done using the formula:

I = P/V

I is current in amperes, P is power in watts, and V is voltage. In Indonesia, the typical household voltage is 220 volts. Continuing the previous example:

I = 375 watts: 220 volts = 1.70 amperes

3. Adding a safety margin

To ensure that the MCB does not trip due to momentary power surges (such as when powering appliances with electric motors), add a safety margin of 25-30%. Therefore, the current calculated earlier is multiplied by 125% or 1.25 as the safety factor (safety margin).

I x safety factor = 1.70 Amperes x 1.25 = 2.13 Amperes

4. Selecting an available MCB size

After calculating the safe current, select the size of MCB available in the market that is closest but not smaller than the calculated current. MCBs are generally available in sizes 2A, 4A, 6A, 10A, 16A, 20A, and so on. In this example, the most suitable MCB size is 4A.

Additional Factors to Consider

In addition to some of the above, some of these factors can be your consideration in determining the amperage of the MCB.

Load type

Appliances with electric motors such as air conditioners or refrigerators require MCBs with special characteristics, such as type C or D that are able to handle high initial current surges.

Cable length

The length of the cable also affects the size of the MCB. The longer the cable, the greater the resistance and voltage drop that must be considered in the calculation.

Environment

The temperature of the environment in which the MCB is installed also affects its performance. At high temperatures, MCBs may require derating (reduction in nominal current).

Thus, determining the amount of MCB amperage should not be done carelessly. The steps described above can help you choose the right MCB size to protect electrical circuits.

Choosing the right MCB can prevent damage to electrical equipment, reduce the risk of fire, and ensure that the electrical system works efficiently and safely. Do not hesitate to consult an electrician if you are unsure about the amperage of the MCB you need.