UL listed lights state a maximum of 210 watts can be connected when using 22 gauge wire (the thinnest wire in use, typical of mini-lights). In this case, most traditional incandescent Christmas mini lights only allow you to connect 4 or 5 sets end to end but with many LED mini light strings you can connect 40 to 50+ together depending on the light count.
Consider your circuits:
- Most household circuits are 15 or 20 amps
- 15 amp circuits support 1,800 watts at 80% capacity (maximum recommendation)
- 20 amp circuits support 2,400 watts at 80% capacity (maximum recommendation)
Calculate your total number of bulbs times their wattage to plan maximum string connections and outlet capacity. Visit this great site to learn more about holiday lighting details like comparing the cost to run older incandescent lights to new LED lights.