How to size a generator

When choosing the right generator, you must first decide how many circuits or rooms in your home or small business you should protect. The more circuits that require protection, the larger the generator you need.

The automatic transfer switch in pre-packaged, air-cooled systems allows you to match the system's load center circuits to the amperage in your home's main distribution panel (see Figure A). Simply determine which circuits to protect during an outage and choose a generator. There is no need to add up wattages, since you'll never use all appliances on every circuit at the same time.

(Figure B) is an example of the circuits that can be protected with a 16kW (16 circuits) air-cooled generator.

For whole-house protection or commercial applications, GUARDIAN'S liquid-cooled models range from 20 - 45kW in single phase and GUARDIAN Elite commercial models range from 60-150kW in single and three phase voltages.

To get accurate sizing requirements for a liquid-cooled generator, a licensed electrician will need to apply an amp meter to the circuits and appliances that are intended to operate on backup power.

Note: Rooms and appliances are shown as examples only. You may choose other items that better fit your needs. Due to the cycling nature of some appliances all items may not be able to run simultaneously. (*) 240V 2-pole circuit breaker is equal to 2 circuits. (A) For smaller central air conditioning units only. Check A/C starting requirements.

Starting requirements for older and/or less efficient equipment may exceed recommended generator capability. Consult an electrician for starting requirements.