Safety Rules for Using a Portable Generator

a yellow and black portable generator

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Portable generators can really save you in a power outage, but they can also kill you if they aren’t used properly. Generators typically burn gasoline or another fossil fuel, and they create two potentially deadly elements: carbon monoxide and electricity. There are three cardinal rules to follow for safe use of an electrical generator:

  • Run portable generators only where they can be fully ventilated.
  • Use the electrical power produced by a generator as directed.
  • Use safe practices when refueling a generator.

How Portable Generators Work

A portable generator works by converting mechanical energy to electrical energy, in much the same way that a utility power plant does it—except on a smaller scale. All generators create an electrical field by spinning a shaft that rotates wire coils (armature) between the north and south poles of magnets. In the case of a portable generator, the spinning motion of the coils is created by a combustion engine that turns the armature shaft, much like a gas lawnmower spins a blade.

The motion of the wire coils inside a bank of magnets energizes the electrons in the wires and creates electricity that can be harnessed to feed plug-in outlets on the generator. A portable generator includes an alternator that creates 120-volt alternating (AC) current that can be used by standard appliances and tools.

Safe Practices for Using a Generator

A portable generator is quite safe to use if you follow certain practices.

Run Generators Outdoors

All portable generators burn fossil fuels and create carbon monoxide (CO), a deadly colorless and odorless gas. For this reason, portable generators must be fully ventilated at all times when they are running. It is not safe to run a generator indoors or even in a garage unless the garage can be completely open for ventilation, which generally means opening multiple doors to provide cross-ventilation. Think of it this way: If a space isn’t safe for running a gas lawnmower or a car, it also is unsafe for a portable generator.

If a generator is outdoors near a door or window, make sure the door or window remains closed so that no exhaust from the generator gets indoors.

Use the Right Extension Cords

Since you’re running your generator outdoors for safety, you’ll most likely need extension cords to bring power into the house. But it’s important to note that not all extension cords are equal. Just like the wiring in your home’s walls, cords have a limited capacity for carrying electricity. Heavy-duty cords with thick wires can handle more electricity than thinner cords with lighter-gauge wire. Length is another factor, due to the resistance factor that occurs as distances increase. A 25-foot cord offers a slightly higher capacity than a 100-foot cord with the same wire size. Using an undersized cord can overheat the cord, melt the cord insulation or plugs, and create a potential fire or shock hazard.

The rule here is to use cords that can safely handle the electrical demand, or load, of the appliance of the device that is plugged into the cord. Electrical load is measured in watts. To run a 3,000-watt space heater, the cord must be rated for more than 3,000 watts.

However, extension cords are typically rated in amps (amperage) rather than watts. Fortunately, amps, watts, and volts exist in a mathematical relationship that makes it is easy to determine the wattage rating. The formula is: Wattage = Volts x Amps.

To convert the amperage rating of an extension cord to a wattage rating, multiply the amp rating by 120 (the line voltage of the circuit). For example, if the cord is rated for 12 amps, the total load capacity of the cord is 1,440 watts (12 x 120 = 1,440). However, it is best to reduce the total capacity by 20 percent, which produces a “safe capacity.” To make this calculation, simply multiply the wattage by 0.80. Therefore, the safe capacity for a 12-amp cord is: 1,440 x 0.80 = 1,152 watts. In this example, you can use safely use this extension cord with any appliance with a wattage rating of 1,152 watts or less.

In addition to using the right size cord for the electrical load, always use grounded, or 3-prong, extension cords with a portable generator. Grounded cords provide a safe path for electricity to follow in the event of a short circuit or other electrical hazards.

NEVER Back-feed a Household Circuit

Back-feeding a household circuit is the extremely dangerous practice of connecting a generator to an electrical outlet with a modified extension cord that has two male (pronged) plug ends. This energizes the entire circuit via the outlet, creating a serious fire hazard as well as a deadly shock hazard for utility workers working on power lines in the area. In the event of a power outage, utility workers generally assume that all affected households have no power. But if a single homeowner is back-feeding a generator into his home's wiring, it introduces an unauthorized power source into the system, putting the workers at risk of electric shock.

The only safe way to provide power to household outlets and hard-wired appliances is to use a manual transfer switch installed by an electrician. These switches cost around $1,200 to $1,500, including installation, and they allow you to safely power a few select household circuits with a portable generator.

Otherwise, the only safe way to use a generator to power appliances is to run properly rated extension cords directly from the appliances to the generator plug-ins.

Turn off a Generator Before Refueling

Never add gas to a generator while it is running or when it is hot. Gasoline spilled onto a hot engine can ignite, creating an instantaneous fire and possibly an explosion. Before refueling a generator, turn off the motor and let it cool down completely, which may take 15 minutes or so. Going without power for 15 minutes won’t kill anyone, but a gas fire or explosion certainly can.