Can You String Too Many Christmas Lights Together?

by | Nov 1, 2019

Short Answer: Yes! The number of light strings that can be run in series is limited by the types of bulbs on the string, how much power they use, the length of the string, and the type/gauge of the wire used in the manufacture of the lights.

Longer Answer: For pre-wired Christmas tree lights and light strings sold with an Underwriters Laboratory (UL) the maximum power added together of a series of lights plugged end to end is 210 watts.

For example, if a string of lights is rated at 50 watts then only 4 sets of lights can be run in series.

So, an LED light string with a rating of 2.4 watts can be run over 80 sets in series.

Exception to this Rule: This rule does not apply to traditional C7/C9 bulbs and cords (the style you might remember from your childhood). These cool retro style Christmas lights can only be run a maximum distance of 250 feet if they are constructed with 18 AWG/10 Amp wire.

Shorter 25-foot 20 AWG cords are generally spec’d to be run only two cords in series.

Conclusion: Yes, you can only run so many light strings in series. Be sure to check the manufacturer’s specifications of any lights you are shopping for and make a note of that number on your Christmas lights inventory spreadsheet after the purchase.

Have other technical questions? Post them in the comments below!

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2 Comments

  1. Connie Doyle

    We have a very large family room and buy a giant live tree. I love lots of lights and I like to put 2400 lights on my large Christmas tree, using 8 strings of 300 miniature lights. Does that mean I’d have to use 2 extension cords, one for each set of four strings?

    Reply
    • Shellie

      Thanks for your question.

      How you electrically organize your light sets during installation all depends on what types of lights you are using. If you are working with LED sets then you will have more flexibility since they can be run longer in a single series than incandescent lights. (So, the short answer here might be, not necessarily!)

      So, first, check to see what types of lights you are using to answer that question.

      As a note, it’s uncommon to see incandescent strings come in 300 lights to the set so more than likely, you are working with LED. That being said, we’ve seen everything. So take a close look at either your packaging or the tags that should be next to the male plugs on the light sets. The packaging and/or tags should tell you how many sets you can safely run in series.

      If your light strings turn out to be incandescent, then you would have to use a splitter or plug different circuits into the end plug of one or two extension cords, making sure there are not more than 210 watts in a single connected series of light sets. (That’s a long sentence!) Also, verify that the total wattage of the sets plugged into your extension cord and into a single house circuit doesn’t exceed the rating of the extension cord(s) or your breaker.

      Moving forward, you might also consider, using light strings that don’t have so many lights per strand. I have found that installing shorter light sets makes it easier to wrap the branches and easier to replace if a set should go out. Wrapping those long strings in a ball like knitting yarn will help your job go more smoothly on tree lighting day.

      One quick extra tip: Be sure to use a surge protector when you plug in your lights, especially if they are LED.

      Hope this helps! Let us know if you have other questions.

      Shellie

      Reply

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