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Electrical Service Panel: How to Calculate Electrical Load Capacity

No matter how enticing it is to purchase the new upgrades of appliances, calculating first the limit of your electrical load capacity will surely place your household in the margin of safety.

Basic knowledge on how to calculate your home’s power capacity is essential. This knowledge is necessary when you are planning to install new appliances or considering to update your home’s electrical service. It is also a good indicator of whether adding a new channel is a need, or if moving some appliances to another circuit is necessary. 

But how do you know if your electrical power service is appropriate, or when to know if you need an electrical service to extend capacity? Determining this requires a little math to evaluate the total load capacity of your home. Here’s a guide on how to do it. 

Understanding Electrical Load Capacity

Before anything else, get to know first what electrical load capacity is and understand how it is used in the overall calculation.

Electrical load capacity is the total amount of power provided by the main service for your home’s electricity usage. A total electrical capacity of the electrical service panel is calculated in amperage (amps). 

Moreover, calculating how much energy your home requires is a matter of measuring the amperage load of all the different appliances and fixtures in order to keep your home safe. It is commonly recommended that the load never exceeds 80 per cent of the capacity of an electrical service panel.

To calculate load capacity, you need first to understand the simple relationship between watts, volts, and amps. A relationship principle known as Ohm’s Law states that:

Amperage (A) x Volts (V) = Watts (W)

By restating this calculation, it can also measure volts (V= W/A ) and amperage (A= W/V).

Steps in Calculating Electrical Load Capacity

Step 1. You have to isolate the power point or circuit that you want to measure. Take the breaker’s size and multiply it by the rated voltage. For example, if you have a 20 amp breaker operating at 120 volts, it will have a maximum load of 2400 watts (20 amps x 120 volts). The National Electric Code recommends that the overall capacity of the load does not exceed 80 per cent, so 2400 watts is not yet the final load capacity. 

Step 2. After getting the maximum load, calculate the recommended maximum, which is you multiply the breaker’s maximum capacity by 80 per cent. The result is equal to 1920 watts (2400 watts times 80 per cent). It means that the 20-amp circuit has a realistic capacity of 1920 watts, so be careful on what appliances you plug in, circuit breaker might trip if it overload.

Step 3. To get the total load capacity of the 20 amp breaker, you must identify all the devices and appliances that are connected to the circuit that you chose. Check every device to see how many watts it uses. Then, you write down every device’s wattage. If the wattage is not given, multiply the device’s voltage by how much current it uses to get the power in watts.

Step 4. To have the total load on the circuit, add the wattage of all those devices together. Take the total load, and divide by the overall recommended load to get the percentage. For example, if the total load is up to 800 watts and this is a 20 amp circuit, then the load usage is 800 watts divided by 1920 watts equal to 0.416 or 42%. 

This means that the 20 amp circuit breaker is running at 42% of its suggested maximum load – the 2400 watts, so there’s no need to worry for an upcoming danger. You can now order new appliances; you already know it wouldn’t exceed the electricity limit of your home.


Renewing and adding appliances and fixtures at home adds beauty, but with too much load capacity, it is hazardous. Calculating your home’s electrical load capacity is necessary when you have future plans of buying new appliances or extending your electrical load. This is very helpful for you to avoid appliances damage and possible danger in the future. 

But if you’re unsure of your calculation on your load capacity or having a difficult time calculating, contact a reliable and trusted level 2 electrician from Sydney North Shore Electrician now to ensure your home’s safety. 

With our highest quality of electrical services, expertise and mastery in all electrical works, you may leave all electrical matters in our hands and turn your attention to other things that would benefit you, your family and business.

Furthermore, wherever you are in Sydney, working with your local electricians means faster response time.

Call us at (02) 8378 2828 for an appointment or book online now.

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