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Instead of using this precise method of calculating loads you can use values "off of face plates" on equipment or the values shown on the Wattage Guide.

If you have no name plate data or the device is not listed on the Wattage Guide the follow the instructions here to determine the full load or device load.

For calculating full loads follow the procedures shown below. If you have an amp meter and you knsow how to use it, you can run the load and use a meter to determine the Running Load Requirements.

Picking the right size generator to meet your needs is not that complicated. There are several electrical parameters you need to be concerned with to make a proper selection. 

Voltage Requirements
In the United States most applicances operate on 120 volts alternating current commonly called VAC. The most common electrical service is 120/240 VAC. If you need to power 120 volt and 240 volt equipment make sure the generator you select is capable of both voltages. If you only need 120 VAC you can use a generator that only has 120 VAC. Portable generators often have half the generators power on one set of outlets and half on the other set of outlets.  You cannot connect both sides together to increase the capacity.

Running Load Requirements
Running load is the total amperage of all equipment running at one time. The name plate on the equipment will generally have this amperage displayed. If no name plate is available use an amp meter to meaure the amperage. All builidngs have a utility meter and those meters show kilowatt-hours used. Modern meters show kW or the 1000's of watts that you are using. You can read the kW being used and then turn on the equipment and read the meter again. Subtract the second reading from the first reading and you will then know the watts used by the equipment you turned on.  You can also use a stop watch and count rotations of the horizontal disk when the lis operating operating. See tbelow. You can estimate the total running load by adding up the running wattages of all items to be powered. If the name plate show only amps and voltage the wattage can estimated by multiplying volts times amps to calculate watts. Amps times Volts equals Watts.  The watts total divided by 1000 is kW.

Starting Load Requirements
Generators must have enough power to "start" the equipment that you want to power. In general motors require additional amperage to start. To determine the starting amps use a digital amp meter with a peak hold feature that will capture the highest amperage when you start the equipment. If you have a manual on the equipment look for LRA or "locked rotor amps" or "maximum amps" which is the amperage it takes to start the motor. You can also call the manufacturer or supplier of the motor and ask them what the LRA is for the model of equpment you have.  A rule of thumb is a generators will start a motor up to 1/5th the horsepower of the engine. A 5000 watt generator driven by a 10 horsepower engine will start a 2 hoursepower motor.

Typical Running Loads
The link shown here shows goes to a page that allows you to caluclate total amperage and typical wattages for various applicances. This is a general guideline and whenever possible use the actual name plate data of the equipment.  Wattage Guide

Additional references:
 These formulas convert data from one value to another. See our Tables and Formulas page.

For other educational information see our Index.

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