Selecting the Best Backup Generator System
Power-Load Chart Estimator (see separate web page link) is a tool to help select the electrical loads the owner wishes to power. It will also help select the appropriate generator size. It will help the owner weigh function (electrical loads to carry) against cost (size of generator needed). The Basic Loads and Variable Loads are entered on the chart.
- Basic Loads will always be connected to the generator circuit. These electrical loads will always have power and can be operated whenever someone uses them.
- Variable Loads are the electrical loads that are manually controlled and therefore can be applied in a sequence that will not overload the generator.
This Load Chart will help indicate which available Variable Loads can be applied confidently knowing that the Basic Loads are always available.
On the Load Chart, enter selected Basic Loads by entering “B” for yes in the “Basic Loads” column. Enter “V” for Variable Loads in the “Variable Loads” column. Enter an “X” in the “Not Used” column for loads never intended to be powered by the generator set when utility power is out. Enter different wattages (see manufacturers nameplate for wattage [watts = volts x amps]) for any load by simply changing the existing value in the “Typ. Wattage” column. The total of Basic Loads plus necessary Variable Loads determines the minimum wattage rating generator set required. When the generator is operating, Variable Loads plus Basic Loads should not total more than the rated wattage of the generator selected. We suggest trying different combinations of electrical loads to get the desired combination of Basic & Variable Loads.
Using the attached Manual Load Chart, the wattages are simply entered in the appropriate columns and totaled to determine the minimum wattage rated generator set required.
For best operating practice, the average electrical load on the generator set should not exceed 80% of the generator’s maximum power rating. Average load requirements should not be a problem since many of the basic loads come on line intermittently (e.g., sumps pump, well pump, furnace fan and refrigerator) and, therefore, will not all start or be running at the same time. Motor starting factors are built into this application guide for the loads listed. Some motors need additional wattage to start and then fall back to their rating shown on the manufacturers nameplate. Use the “starting amps” value on the motor nameplate to calculate the motor starting wattage required from the generator, (watts = volts x amps). The maximum motor starting wattage for the RS 12000 generator set is 1.6 times the nameplate rating on the generator set.
Alternately, connecting the generator to the entire house distribution panel allows all loads to be selectively powered, but this requires the homeowner to be more careful to limit electrical loads applied to the generator set. (See the RST Transfer Selection Guidelines for more information on selecting the appropriate interconnection method.) If certain electrical loads are identified and isolated for use by the generator when using an electrical sub-panel, the Basic & Variable Loads will not overload the system.