It’s a common goal when hanging Christmas lights: you want to string together as many lights as you can and power them using the least number of AC outlets as possible. But you don’t want to overload your electrical system in your home.
So how do you determine how many strands to plug into one outlet? By using this formula:
Number of total bulbs = Volts from your outlet X amps on your circuit X 80%/Wattage from a single lamp
It’s not as hard as it looks. First, most AC outlets have 120 volts, and most home electrical circuits are either 15 or 20 amps. The packaging on your Christmas lights will tell you how many watts each bulb puts out.
So for example, if you’re working with a standard AC outlet on a 15-amp circuit with traditional 5-watt C7 bulbs,
Number of total bulbs = 120 volts X 15 amps X 80%/5 watts
= 288 bulbs
Generally, traditional bulbs run between 5 and 10 watts each, while LED bulbs can be just one watt or less.