The power capacity of different generator models varies as widely as the appliances they power. If your power goes out, you’re probably less concerned that your electric stove doesn’t have power than you are about the basement flooding because your sump pump doesn’t work. The length of time the power is out and the time of year may also make a difference in choosing which appliances you supply with emergency power from your portable generator. Understanding your generator’s power capacity is the first step in knowing what you can power, and what you will power in the event of an outage.
Understanding Power Output
Power is measured in Watts (W), or in Kilowatts(kW). One kilowatt equals 1000 watts. Watts are calculated by multiplying voltage by amperes. A device that runs on 120 volts and draws 5 amperes uses 600 watts (120V x 5A) of power. On some appliance tags, this is expressed as Volt-Amps or VA; others express their power requirements in watts or kilowatts.
Appliances require a certain amount of power, regardless of the voltage level they are designed to run on. At 240 volts, a 600 watt appliance only requires 2.5 amperes of current, but another 600 watt appliance operating at 120 volts needs twice as many amperes. This is why generators are rated in watts or kilowatts, because regardless of the voltage being used, the power output stays the same.
Generators often have two power ratings―maximum or surge power, and continuous power. Continuous power refers to how much the generator is able to supply on an ongoing basis. Maximum or surge power gives you a temporary boost for starting motors. Motors require more power for one to three seconds as they start.
Typical Appliance Power Requirements
The following list gives typical power requirements for starting and running some common appliances. Actual power requirements may vary by manufacturer, motor size and type of motor used. Some appliances don’t use motors and their power requirements don’t change.
- Sump pump: 800 watts, 2400 starting watts.
- Well pump 1 hp: 2000 watts, 6000 starting watts.
- Refrigerator: 700 watts, 2100 starting watts.
- Freezer: 700 watts, 2100 starting watts.
- Furnace blower motor: up to 875 watts, 2625 starting watts.
- Window Air Conditioner 6000 BTU: 700-900 watts, 2100-2700 starting watts.
- Window Air Conditioner 12,000 BTU: 1200-1700 watts, 3600-5100 starting watts.
- Coffee Maker: 1200 watts.
- Toaster Oven 1550 watts.
- Hot Plate: 1200 watts.
- Electric Frying Pan: 1200 watts.
- 1000 Watt Microwave Oven: 1200 watts.
- Electric Lights: 13 to 150 watts per bulb.
Managing Portable Generator Power
Begin by deciding which critical appliances should receive power during an outage. Give top priority to sump pumps, sewage pumps, refrigerators and freezers. Add the furnace to your list in cold weather to keep the house warm and prevent pipes from freezing. Total the power required for each device, and determine the starting watts required. A rule of thumb for motors allows for three times the starting watts. Heavy duty motors may require six times the running watts to start.
Manage your power by only starting one critical appliance at a time. Start the largest loads first and work your way down to the lighter loads. Try to operate loads in cycles. During heavy rain, you might need your sump pump going full time, but if it’s dry, then maybe you don’t need it.
A manual transfer switch that controls your critical loads will help you manage your portable generator power. You can control power to your critical circuits as necessary. They also allow you to power appliances that don’t have power cords, and prevent your generator from back-feeding the utility lines―a serious danger to utility workers attempting to restore power.