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The factors
How many Christmas lights you can plug into a single circuit depends on:
- The type of Christmas lights you’re using (both size and whether they’re LEDs)
- If anything else is also running off the circuit (such as lights and appliances in your home)
- The amperage of the circuit you have (more on this later)
But “it depends” isn’t really an answer. So, here’s how you can calculate how many Christmas lights you can put on a single circuit breaker. (Warning: math ahead.)
Calculating the maximum wattage
To determine the number of lights you can put on a circuit, you have to calculate how many “watts” of bulbs your circuit can handle. The equation for that looks like this: watts = amps x volts.
Now, we know 2 of these variables.
- Volts: Household outlets are 120 volts.
- Amps: Most Florida homes have either 15-amp or 20-amp circuits.
For example, a 15-amp circuit can handle 1800 watts (15 amps x 120 volts).
However, this is the absolute maximum. We recommend loading your circuits to no more than 80% capacity. This prevents the possibility of wires overheating and becoming a fire danger.
That said, a 15-amp circuit can safely handle 1440 watts (80% of 1800 is 1440).
If you have any other lights or appliances on this circuit, subtract the wattage of those devices from the total.
For example, if the circuit you’re using for Christmas lights also handles 3, 60-watt bulbs on your porch and in front of your garage, you need to subtract the 180 watts from the 1440 total.
This is where the type of Christmas lights you use really matters. Different sizes and types have different wattage affecting the number of lights you can put on a single circuit.
For example, say a string of small LED lights only uses 12 watts. So, you could, put 105 strings of those lights on a single circuit (1440÷12=105).
However, a single circuit could only take 11 strings of large, incandescent bulbs that use 125 watts (1440÷125=11.5).
This brings up a couple of other questions...
Read more on LED vs incandescent energy usage in our blog, "This Common Holiday Decoration Sucks Up 80% More Energy".
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How many lights can I string together, end-to-end?
Just follow the instructions on the package of the lights you are buying.
The number of lights you can string together is determined by the UL (Underwriter’s Laboratory), an independent safety science company. They’ve done the math for you!
How many Christmas lights can I plug into an outlet or power strip?
Math to the rescue, again! The lowest amperage rating sets the limit for the number of Christmas lights you can plug into a single outlet.
For example, let’s say you have a 15-amp, 2-outlet electrical box on a 15-amp circuit. You connect a heavy-duty 12-gauge extension cord into one of the outlets and a 15-amp power strip at the end of it. The 12-gauge extension cord is rated to 20 amps.
However, since your power strip is only 15 amps (along with your circuit and outlet), that’s the maximum amperage for your power strip. Now, that does not mean every outlet in the strip can handle 15 amps. That’s the total it can handle.
For example, if you have 5 strings of 40.8-watt mini lights connected end-to-end and plugged into the power strip. How many more of these can you add?
Use the same formula as above, rearranged a little bit to figure it out. First, we need to determine the amps that the 5 strings are pulling.
Amps=watts÷volts
Since each string is 40.8 watts, we know that each string needs 0.34 amps (40.8÷120). Five of those together is 1.7 amps.
The power strip has 6 plugs on it. 1.7 x 6 = 10.2 amps. So, the 15-amp power strip, filled with 6 of these 5-string lengths would be safe.
Now, remember, we still have to take into account the limit of the circuit that we talked about in the first section. This is where many people go wrong. Each outlet cannot have 15 amps worth of Christmas lights. Your circuit sets the maximum limit.
In our example, 10.2 amps is being used in that outlet, so you can only use 1.8 amps more on the entire circuit. (80% of 15 amps is 12 amps.) So even though there are 3 other outlets on the same circuit, you can only really put 5 more strands on the entire circuit.
The best solution: separate electrical circuits
If you plan on putting up a lot of Christmas lights, we recommend running separate electrical circuits dedicated to the lights. This gives you peace of mind knowing there is nothing else plugged into the circuit.
And, bonus, you can also put outlets where they’re more convenient, so you don’t have to run as many extension cords (fewer cords is always a safer option).
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