Choosing extension cords for a generator

If you are not using a transfer switch, extension cords carry power from the generator to your appliances. The wrong cord can overheat, waste power, and create shock and fire hazards.

Use outdoor-rated, heavy-duty cords

OSHA and the CPSC advise using heavy-duty, outdoor-rated extension cords that are in good condition and rated for the load. Look for a jacket rating for outdoor use and a three-prong grounded plug. Never use cords with cuts, crushed insulation, or missing ground pins.

Gauge matters

Wire size is given as AWG gauge; smaller numbers mean thicker wire that can carry more current. Cord packaging lists the maximum amps or watts. As a general guide for 120-volt cords:

• 16 AWG: light loads, such as lamps and chargers, on short runs.
• 14 AWG: moderate loads, such as a refrigerator, on shorter runs.
• 12 AWG: heavier loads (up to about 15 to 20 amps, depending on the cord’s rating) and longer runs.
• 10 AWG: heavy loads or long runs.

Always follow the rating printed on the cord. Longer cords lose more voltage, which makes motors run hotter, so step up a gauge for long runs.

Length: long enough to be safe

The generator has to be well away from the house, more than 20 feet from windows, doors, and vents per CDC guidance, so cords need to be long enough to reach without tempting anyone to move the generator closer. Run cords where they will not be crushed by doors or driven over, and do not run them through windows that then must be left open.

Do not daisy-chain or overload

Plugging cords into cords, or loading many appliances onto one light cord, invites overheating. Use one properly rated cord per heavy appliance, or a generator power cord designed to split to several outlets.

Never backfeed

Never plug a generator into a house outlet or use a “double-male” cord. It is illegal in many places and can electrocute utility workers. NFPA is explicit on this point.

When cords are the wrong answer

Hard-wired loads such as furnaces, well pumps, and ceiling lights cannot be safely powered with cords. That is the job of a manual transfer switch or interlock kit installed by an electrician. See transfer switch vs interlock.

Watts, amps and volts: a quick conversion

Cord labels list amps, and appliance labels often list watts. For 120-volt equipment, amps = watts ÷ 120. Some examples:

Load	Approx. running watts	Approx. amps at 120 V
LED lamp plus phone chargers	60	0.5
Refrigerator (running)	700	5.8
Window air conditioner (10,000 Btu)	1,000	8.3
Microwave (1,000 W cooking)	1,500	12.5
Space heater (high)	1,500	12.5

Starting surges for motors, such as a refrigerator compressor, can briefly be two to three times the running draw. A cord that's rated right at the running amps has no margin, so pick one rated comfortably above the load. Use your appliance's own label rather than these typical figures, and see starting vs. running watts.

Voltage drop on long runs

Every foot of wire has a little resistance. On a long, thin cord, that resistance turns some of your power into heat and lowers the voltage at the far end. Motors are the most sensitive: a compressor that sees low voltage draws more current, runs hotter, and may struggle to start. As a rule of thumb, if the cord is longer than 50 feet, or the load is a motor near the cord's limit, choose the next heavier gauge (a smaller AWG number). A cord that's warm to the touch along its length is telling you it's undersized or overloaded.

Generator-side connections

Many portable generators have both standard 120-volt household-style outlets (NEMA 5-20R duplexes) and a larger locking outlet, often a 30-amp L14-30 four-prong twist-lock that provides 120/240 volts. The locking outlet is intended for a generator power cord that feeds a transfer switch or interlock inlet, not for a homemade adapter. Some "spider box" style splitter cords break a single 30-amp outlet into several protected 120-volt outlets. These can be useful for running several cords, but only buy listed products with built-in circuit protection.

Protecting cords outside

• Keep connections dry. Ready.gov warns that touching a wet generator or devices connected to one can cause electrical shock. Keep plug-and-socket connections off the ground and under cover, or use a listed weatherproof connector box.
• Avoid pinch points. Don't run cords under doors or through windows that then can't close, because that can also let exhaust into the home.
• Avoid trip and vehicle hazards. Run cords along walls, and use cord covers across walkways.
• Uncoil fully. A tightly coiled cord carrying a heavy load can overheat.

Inspecting your cords before an outage

Do this once a season, not during the storm:

1. Unroll each cord and look along the whole length for cuts, flattened sections, or exposed conductors.
2. Check that the ground pin is present and straight.
3. Check that the plug and receptacle ends aren't cracked, loose, or discolored from heat.
4. Confirm the label: gauge, amp rating, and outdoor rating.
5. Label each cord with its gauge and length so you can grab the right one in the dark.

Store cords coiled loosely in a dry bin along with the generator's fuel, oil, and manual, so everything you need is in one place.

How many cords do you need?

Count the appliances you'll actually run, and plan one cord per heavy appliance: refrigerator, freezer, window AC, or space heater. Lighter loads, such as lamps, chargers, a TV, or an internet router, can share a cord with a power strip, if the total stays within the cord's rating. Most households end up with two or three heavy-duty cords and one medium cord. If you find yourself needing more than four, that's usually the point where a transfer switch or interlock with a single generator inlet becomes the cleaner and safer solution.