How to Calculate Load

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Electrical power is a necessity of life in today's world. It seems just about everything requires electricity to operate. Those that plan for backup power in case of catastrophe need to know how much power they need to continue life unhindered. Generators are usually the best choice for a backup source but without knowing the electrical load of your home, it becomes mere guesswork as to how big of a generator you need to acquire. Measuring the electrical load of your home includes measuring the appliances, lighting and other electrical devices that you need to run. The best way to measure the load of your home is to measure the electricity draw reported by the power meter on your electrical feed from the power company. By checking your meter at different intervals throughout a few days you will have the best estimate of your entire home electrical load.

Things You'll Need

  • Calculator
  • Stopwatch
  • Locate the electrical meter for your home. This is located at the point where the electric company provides power to you. The meters resemble a glass bubble with a face plate that indicates power usage on dials and a rotating disk.

  • Schedule various times during the next few days to go out and take meter readings. These should include times when your electric usage is at a minimum, at a maximum and at a time when usage is average.

  • Record the wheel multiplier for use in the calculations. Every revolution of the wheel is equal to a particular number of watts of energy. The value of each revolution is printed on the face of the meter. It is designated by the symbol Kh printed on the right side of the face plate.

  • Take your reading by watching the spinning wheel in the meter. Count how many times the wheel goes around during the amount of time measured by the stopwatch. To get a good estimate of the usage, especially during peak times when the wheel is moving fast, choose a time period that includes as many revolutions of the wheel that you want to count, between 6 and 10 is a safe number. Begin the stopwatch as the black mark on the wheel passes the middle point of the visible region of the wheel. Count the revolutions until you reach between 6 and 10 revolutions and then stop the stopwatch when the wheel returns to the middle part of the visible region again.

  • Calculate the energy usage for each time when you measured the wheel over the past few days. Use the equation, watts = (Kh Rev 3600) / T, where T = time in seconds, Rev = number of revolutions of the wheel, Kh is read from the meter and 3600 is number of seconds in 1 hour. For example, assume that the meter took 13 seconds to go around 6 times on a meter that had a multiplier value of 3.6. Insert the values that were collected into the equation and calculate the answer.

    Watts = (3.6 6 3600) / 13 = 5,981.5 watts. If this data was for the period of most usage, then a 6 kW generator would work, but not if anything else was added to the home.

Tips & Warnings

  • While this calculation will tell you how many watts you use at any given point in the day, you must account for the extra usage every time an appliance or device starts. There is an added amount of energy needed to start a device.
  • You should select a generator that provides your energy needs with an extra 15 percent available for unexpected changes in your power usage.
  • If you purchase a generator, make sure you select one that has both 240V and 120V outlets.

References

  • Photo Credit Hemera Technologies/AbleStock.com/Getty Images
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