How to String Christmas Lights

White Christmas lights against a blue background.

When the holiday season is approaching, it’s time to start thinking about decorations and that includes Christmas lights. With colorful bulbs and twinkling lights dancing around the room or adorning the outside of your home, the rainbow of colors creates a festive environment for everyone to enjoy. Connecting strings of Christmas lights in a continuous series is one of the necessary steps in creating the look you want to achieve while keeping your home, inside and out, safe from overheating bulbs. Here's how to do it with safety in mind.

Connecting the Lights

Whichever type of lighting you choose (incandescent or LED), there are things to keep in mind starting with the rating of the lights. When connecting the lights in a series, be aware of how many watts the string is rated for so you can create a series of connected lights while staying within safety limits. Keep in mind that lights such as pre-wired LED strings and mini lights have a maximum connectivity rating determined by its UL (Underwriters Laboratory) guideline of 210 watts. The maximum connectivity is the maximum number of strings of lights that can be connected in a series (end to end) one circuit.

Calculating Maximum Connectivity

A soft-focus Christmas tree with lights.

A simple calculation is required to arrive at the number of lights you can connect in a series. For this, you will need to know how many watts your string of lights is rated for. For example, if one string of lights has a 20-watt rating, you would divide the UL of 210 watts by the wattage for one string. In this example, it’s 20 watts per string, which equals 10.5 strings. (210 watts /20 watts=10.5 strings in a connected series).


If you plan to run many strings of lights, whether indoors or outdoors or both, it's very important that you don't overload the breaker. A basic rule to follow is to not use 100 percent of the wattage of the breaker; instead, keep it at around 85 percent wattage usage.

Surge Protector

A strand of colored Christmas lights against a white background.

If you’re planning to decorate outdoors with LED lights, it's best to plug the connected strings into a surge protector rated for outdoor use. (A standard surge protector can be used indoors.) Both surge protectors provide protection to the lighting in the event there is a surge of power on the electrical line.

Safety Tips

Like anything electrical, safety comes first and this includes Christmas trees. With this in mind, there are several things to add to your safety checklist.

Incandescent bulbs draw more electricity than LED bulbs, which means they get hotter. If the lighting is too close to other decorations, it can ignite a fire.

Use LED bulbs, which do not generate as much heat as incandescent bulbs.

Do not allow pets to play in, under, or around the Christmas tree as they may cause it to tip over or readjust ornaments, putting them in danger of the bulb’s heat.

Keep the light’s wiring contained and out of reach of dogs, puppies, or even cats that may have a tendency to chew the wires.

Never leave the Christmas tree on all night or while you are not home and it’s unattended.

As an added safety measure, wrap a piece of electrical tape around each section where you’ve joined one string of lights to another string.

With the proper connecting of a series of Christmas lights, you will have a safer and merrier holiday.