How to calculate connected electrical loads

Written by michael logan
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How to calculate connected electrical loads
Electrical loads are expressed as amperes. (Ancien Ampèremêtre image by slinge from

Calculating connected electrical loads is important to prevent blowing fuses or tripping circuit breakers, since this usually happens when the circuit is overloaded. An electrical load is how much current a device draws when it is operating. Current is expressed in amperes and power is expressed in watts or kilowatts. Power (P) is calculated from voltage (V) and current (I) where P= I x V. You can calculate current from power by a similar formulas where I = P / V.

Skill level:


  1. 1

    Find the current draw of each device on a circuit. Some devices like a vacuum cleaner will have the current requirements stamped on them. Other devices like a hair dryer may show how much power they use in watts or volt-amps, such a blow dryer for hair or an electric light bulb. Record the power or current requirements of each device on paper.

  2. 2

    Convert the power or current requirements recorded for all devices to amperes. Divide watts or volt-amps by volts to get amperes. Most receptacles in a house provide 120 volts while electric ranges and electric dryers usually 240 volts. If a device gives the current requirements as Milli-amps or Ma, simply divide by 1000 to get amperes. 500 Milli-amps = 0.5 amperes.

  3. 3

    Add up the current requirements in amps for all the devices connected to a circuit. The resulting number is the total connected load for the circuit, expressed in amperes.

Tips and warnings

  • If you have a clamp style ammeter, you can measure the load of a device that does not list its current requirements for power usage.

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