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Christmas Light Timers and Outdoor Extension Cords: What to Buy

Updated November 1, 2026 · General information, not electrical or safety advice

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The short answer: For Christmas lights, use a cord rated for outdoor use (a W in its letters). The University of Texas at Austin table says a 16 gauge cord covers lights up to 13 amps at 25 or 50 feet and up to 10 amps at 100 feet. At 150 feet it calls for 14 gauge for up to 7 amps. Use one timer for each outlet or zone, and do not plug cords into each other.

Safety first. Use only lights and cords rated for outdoor use, plug them into a GFCI-protected outlet, keep ladders and light strands at least 10 feet from overhead power lines, and have a helper. Hire a licensed electrician for any wiring or new outlet. See our safety guide. This reminder is ours; the sourced details are on that page.

Pick the cord

Add up the amps of everything on the cord first. The 1000Bulbs lighting retailer says amps equal watts divided by 110. The University of Texas at Austin (UT) factsheet is adapted from OSHA and lists "Christmas or work lights" in its table.

Cord length	Device rating	Minimum gauge (UT table)
25 ft	1 to 13 amps	16 gauge
50 ft	1 to 13 amps	16 gauge
100 ft	1 to 10 amps	16 gauge
150 ft	1 to 7 amps (Christmas lights)	14 gauge

Source: University of Texas at Austin EHS extension cord factsheet. A lower gauge number means thicker wire. 1000Bulbs gives a different chart (16/2 or 16/3: 13 A to 50 ft and 10 A for 50 to 100 ft; 14/3: 15 A to 50 ft and 13 A for 50 to 100 ft), and says for Christmas lights use 16 gauge for runs of 25 feet or less and 14 gauge for longer. When sources differ, use the thicker cord and read the cord's own label.

Read the letters on the cord

Letter	Meaning (UT factsheet)
W	Rated for outdoor use
S	Flexible cord for general use
J	Standard 300 volt insulation
T	Vinyl thermoplastic jacket
E	Thermoplastic elastomer (TPE) rubber jacket
O	Oil resistant

1000Bulbs adds that an E jacket is the best pick for extended outdoor use, and that a T jacket can become brittle in cold. UT says do not use an indoor cord outside.

Cord rules

Do not plug cords into one another. South Carolina's fire safety program says so, and says not to overload outlets and to use surge protectors when needed.
Do not use damaged cords. UT says electrical tape is not a solution. Idaho Power says to replace damaged or frayed cords.
Use a 3-wire cord. UT says extension cords must be 3-wire so they can be grounded.
Keep connectors dry and off the ground. South Carolina says above ground and out of snow or water; UT says to limit exposure to moisture with watertight or sealable connectors.
Buy only the length you need. 1000Bulbs says longer runs lose voltage.
Keep heaters off extension cords. 1000Bulbs says heat-producing devices may draw 15 amps or more.

Timers

Illinois Extension and South Carolina's fire safety program both say to turn lights off before you sleep or leave, or use a timer.
The Christmas Light Emporium, a retailer, suggests one outdoor timer for each zone. Our calculator counts one per outlet.
Pick a timer rated for outdoor use. Check the amps and watts on the timer's label against the lights you plug in. We did not find an independent source on timer specs, so this is our advice.

Circuit limits are on the safety guide.

Need an outdoor timer or cord?

Look for a timer and cord rated for outdoor use, and check the amps and watts against what you plug in.

Browse outdoor timers and cords Plan your power

Common questions

What gauge extension cord do I need for Christmas lights?

A University of Texas at Austin table adapted from OSHA lists 16 gauge for Christmas lights up to 13 amps at 25 or 50 feet and up to 10 amps at 100 feet, and 14 gauge up to 7 amps at 150 feet. Check your cord's label.

What does the W on an extension cord mean?

The UT factsheet says W means the cord is rated for outdoor use.

Can I plug extension cords into each other?

South Carolina's fire safety program says not to plug extension cords into one another.

How many timers do I need?

A retailer suggests one outdoor timer per zone. Illinois Extension says to turn lights off before sleeping or leaving, or use a timer.

Related guides

Sources