How to Calculate Electrical Load

Electrical loads on circuits should be calculated to avoid causing damage.
••• electronic circuit image by angelo.gi from Fotolia.com

Electrical circuits have many applications, including household, automotive and electronics. The electrical principles apply regardless of the application. You have a number of components distributed on the circuit that constitute the circuit load. You have a power source. You want to know the characteristics of the load components. You have Kirchoff’s Law, which essentially states that the sum of the load voltage equals the sum of the source voltage. You don’t want to damage any of the components on the circuit, so you calculate the load.

Calculating an Electrical Load in a Simple Circuit

    Calculate the electric load for a simple linear circuit having a source voltage of 9 volts and two resistors in series, each of 330 ohms. The second resistor has a lead that goes to ground. Calculate according to the following equations. Let Power = Voltage * Current (P=VI). Let Current = Voltage/Resistance (I=V/R).

    Apply Kirchoff’s Second Law, that the sum of the voltages around a circuit is zero. Conclude that the load voltage around the simple circuit must be 9 volts. Calculate that the load voltage is evenly distributed across each of the resistors, since they have equal resistance, and that the voltage over each must be 4.5 volts (or -4.5 for purposes of Kirchoff’s Law).

    Calculate I=V/R (current calculation), so that I=4.5/330=13.6mA (milliamps). Calculate P=VI=9*.0136=.1224 Watts. Note that all the load characteristics (Voltage, Resistance, Current, and Power) are now known. Be safe and choose resistors rated at .5 Watts.

    Use a linear circuit simulator online to simulate simple circuits and calculate the load characteristics. Utilize the linear circuit simulator described below called “Linear Technology Spice.” Create a sample circuit and experiment with different load components. Calculate the load characteristics using the voltage, current, resistance (or inductance) and power equations.

Calculate Household Electrical Load

    Calculate the load for a typical single family house using an online electrical load calculator. Utilize an online “Single Family Dwelling Electrical Load Calculator.”

    Enter the square footage of your house. Enter the number of “small appliance circuits” and “laundry circuits,” and refer to an electrical diagram if necessary. Use the default values if the information is unavailable. Enter values for “Fastened Appliances,” “Cooking Appliances,” “Heating or Cooling” and “Largest Motor.” Press “Calculate Load.”

    Note the “Total Computed Load,” the “Computed Amperage,” the “General Neutral Load,” the “Total Neutral Load,” and the “Total Neutral Amperage.”

    Tips

    • Kirchoff’s Second Law: The sum of the source voltage and the load voltages is zero. For the two resistor circuit above, the source of 9 volts and the load voltages of -4.5 volts and -4.5 volts (across the two resistors) add to zero.

Related Articles

How to Calculate 30 KW to Amps
How to Calculate Transformer Load
How to Calculate a Voltage Drop Across Resistors
How to Change Electrical Amps to Watts
How to Calculate Voltage Regulation
An Electrical Engineer's Vocabulary Words
Explain Electrical Ladder Diagrams
How to Convert 12 Volt to 6 Volt
How to Find Wattage With Voltage & Frequency
How to Use a Multimeter for the Beginner
Fun Facts About Simple Circuits
How to Calculate the Field Current in a DC Motor
Types of Electrical Loads
How to Convert mW to mA
How to Measure the Ohm Value for an Inductor
How to Read Transistors
How to Use a Zener Diode to Reduce DC Voltage
DIY Very Simple 60-Hertz Oscillator With a Quartz Circuit
How to Reduce 12 Volt to 6 Volt