How Many Christmas Lights Can You Plug Into One Outlet?

Short answer: a normal 15-amp circuit can safely run about 1,440 watts of lights for a whole evening. A 20-amp circuit can run about 1,920 watts. That limit is for the whole circuit, not one outlet. And each light string has its own limit on how many can be linked end to end. That number is on the tag or the box.

If your breaker trips every time the lights come on, the circuit is telling you it's full. At Cain Electric in Gray Summit, our residential electricians can check what else is on that circuit and add a safe outdoor outlet if you need one.

Here is how to figure out your own setup before you hang a single string.

How many watts can one circuit handle?

A 15-amp circuit can handle 1,800 watts, but lights that stay on for hours should only use 80% of that, or 1,440 watts. A 20-amp circuit can handle 2,400 watts, so 80% is 1,920 watts.

Why 80%? The National Electrical Code calls any load that runs 3 hours or more a "continuous load." It sizes breakers so continuous loads only use about 80% of the circuit (NFPA 70). Holiday lights that run from dusk to bedtime count.

You can find the breaker size printed on the handle of the breaker in your panel.

How do you figure out how many strings you can use?

Add up the watts of everything on the circuit and keep the total under the safe number in the table. Here are the steps:

1. Find the watts on each light string. Look at the tag near the plug or on the box.
2. Add up all the strings and decorations you plan to plug in on that circuit.
3. Add anything else on that circuit, like a garage freezer or a shop light.
4. Compare the total to 1,440 watts (15 amp) or 1,920 watts (20 amp).

Example: say each string you bought is rated 40 watts. 1,440 divided by 40 is 36 strings on an empty 15-amp circuit. But that is the most the circuit can carry. It does not mean you can link 36 strings together end to end. Your own number will depend on the watts printed on your lights.

How many light strings can you connect end to end?

Use the number printed on the light string's tag or box, not a guess. The U.S. Fire Administration says to read the maker's instructions for how many strands to connect (USFA).

That limit is there because the thin wire inside each string can only carry so much. Old-style bulbs pull much more power than LED bulbs, so they usually allow far fewer strings in a row. If the box is gone and you can't find the tag, don't link more than a few old-style strings together.

Why is "one outlet" the wrong way to think about it?

Your outlets share circuits. One breaker often feeds several outlets, and sometimes a whole side of the house.

So the outdoor outlet by your front door might share a circuit with your garage, a bathroom or a porch light. If the garage freezer kicks on while 1,200 watts of lights are running, the breaker can trip. A plug strip with 6 spots does not give you more power. It just splits the same circuit 6 ways.

Here is an easy way to see what is on a circuit:

1. Turn on the lights and plug a lamp into the outlet you want to use.
2. Flip that breaker off.
3. Walk around and see what else went dark.

Do outdoor Christmas lights need a GFCI outlet?

Yes. The National Electrical Code requires GFCI protection on outdoor outlets at homes (NFPA 70). A GFCI cuts the power fast if current leaks to the ground, like through a wet cord or a person.

If your outdoor GFCI keeps tripping after rain, the problem is often water in a plug or a cord connection, not the outlet. We cover that in why GFCI outlets keep tripping and why outdoor outlets stop working after heavy rain.

Also make sure your lights and cords are rated for outdoor use. NFPA notes that some lights are made only for indoor use or only for outdoor use (NFPA tip sheet).

Are Christmas lights a fire risk?

Yes, when the wiring is worn, overloaded or too close to heat. NFPA says nearly half of home Christmas tree fires are caused by electrical problems (NFPA tip sheet).

A few simple habits lower the risk:

• Check every string before it goes up. Throw out any with frayed or pinched wires (USFA).
• Use lights listed by a testing lab, like UL or ETL.
• Turn the tree lights off before bed or when you leave the house.
• Don't run cords under rugs or pinch them in doors or windows. Read more in are extension cords a fire hazard.
• Bring outdoor lights in after the holidays so they last longer.

When should you call an electrician?

Call an electrician if the breaker trips again and again, a plug or outlet feels hot, or you smell burning. Those are signs the circuit is overloaded or a connection is going bad.

It also makes sense to call if you want a big display every year. A licensed electrician can add a new outdoor GFCI outlet or a dedicated circuit near the spot where you hang lights. That way your lights don't fight with your garage or bathroom for power.

FAQ

Can I plug Christmas lights into a power strip? Yes, if it is rated for the use and for outdoors when it's outside. But a power strip does not add power. Every plug on it still shares the same circuit.

Do LED lights really use less power? Yes. LED bulbs use much less power than old-style bulbs, so you can usually run more of them on one circuit. Check the watts on the tag to be sure.

Why do my lights trip the breaker only some nights? Something else on the same circuit is likely turning on at the same time, like a freezer, space heater or hair dryer. Find out what shares that circuit and move one of them.

Is it OK to leave Christmas lights on all night? NFPA says to turn tree lights off before going to bed or leaving home. A timer makes this easy for outdoor lights too.

Need a safe place to plug in?

If your breaker keeps tripping or you need an outdoor outlet where there isn't one, Cain Electric can help. We serve homes in Gray Summit, Pacific, Washington, Eureka and across the St. Louis area. Learn more about our residential electrical services or call (314) 607-8687 for a free estimate.