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.