How much power are you going to need and can you ever have too much?

How much power are you going to need and can you ever have too much?

You’ve got thousands of Christmas lights yet you have no idea how many can be plugged into a typical wall socket. We’re here to help.

Let’s use a simple electrical formula. Power (in watts) = Voltage (in volts) times Current (in amperes) or P=VI which is what engineers like to say (why “I” is an abbreviation for current is a closely guarded secret by electrical engineering purists.)

In the United States, a typical wall outlet is 120 volts and all Christmas light strings are wired to handle it. Your wall outlet is usually wired in parallel to several others and connected to some sort of circuit breaker or fuse, usually 15 or 20 amps. Your goal is to not overload the circuit breaker/fuse. It’s good practice to never put more than 80% load on your breakers/fuses… strictly as a safety measure.

You will have to figure out if the outlet where you want to plug in your Christmas lights is on a 15 or 20 amp circuit breaker or fuse. The easiest way to find out is plug a radio in and turn it up pretty loud. Go to you electrical panel and start turning off circuit breakers or unscrewing fuses. When the radio stops making noise, you’re on the right circuit. The breaker/fuse will tell you how much current that circuit can handle.

If you have a 15 amp circuit with 120 volts and factor in an 80% load, using the P=VI equation (P=V*I*0.8) you can have a total load of (120*15*0.8=) 1440 watts.

If you have a 20 amp circuit with 120 volts and factor in an 80% load, using the P=VI equation (P=V*I*0.8) you can have a total load of (120*20*0.8=) 1920 watts.

Use the chart below to get a pretty good idea how much power different types of Christmas lights consume. There are plenty of exceptions to the chart since there are so many different types of lights. To see if you’re close, check the tag at the plug-end of a new string of lights and it will tell you how much current it consumes… in most cases, it will match up with the yellow column in the table and you can feel comfortable with the numbers

LED’s typically use 80-90% less current than incandescents. There might be a temptation to connect thousands of lights to one string until you can put the maximum load on a circuit. Avoid that temptation. Most copper wire used for Christmas lights is thinner than lamp cord wire and will melt under heavy load. Best practice is to limit any continuous string of lights to just a few amps. Extension cords are cheap compared to rebuilding your home after an electrical fire.

Incandescent
Light String Description
Lights /
String
Total
String
Watts
Total
String
Amps
Total Strings
for 15 amp
Circuit
(80% usage)
Total Strings
for 20 amp
Circuit
(80% usage)
mini-lights (incandescent) 20 16 0.13 90 120
mini-lights (incandescent) 50 20 0.17 70 94
mini-lights (incandescent) 100 40 0.33 36 48
mini-lights (incandescent) 150 60 0.51 24 32
mini-lights (incandescent) 200 80 0.66 18 24
C7 incandescent bulbs
(5 watts each)
25 125 1.04 11 15
C9 incandescent bulbs
(7 watts each)
25 175 1.50 8 10
60 watt light bulb 1 60 0.50 24 32
Compact Fluorescent Light (equal to a 60 watt incandescent bulb) 1 14 0.12 102 137
100 watt light bulb 1 100 0.75 14 19
150 watt floodlight 1 150 1.25 9 12
rope light (incandescent) at 5.5 watts per foot and rope is 18 feet long 216 99 0.82 14 19
LED
Light String Description
Lights /
String
Total
String
Watts
Total
String
Amps
Total Strings
for 15 amp
Circuit
(80% usage)
Total Strings
for 20 amp
Circuit
(80% usage)
C6-C7-C9 LED-light strings
(C6-C7-C9 look-a-likes)
25 2.4 0.02 600 800
5MM, G12, G25, etc. light strings (1 LED per bulb) 50-70 2.6 0.03 554 738
LED
C7-C9 Retrofit Bulbs
Amps
per
Bulb
Total Bulbs
for 15 amp
Circuit
(80% usage)
Total Bulbs
for 20 amp
Circuit
(80% usage)
C7 retrofit (1 watt each) 0.008 1440 1920
C9 retrofit (1.1 watt each) 0.009 1309 1745
Inflatable Description Total
Watts
Total
Amps
Maximum inflatables
for 15 amp
Circuit
(80% usage)
Maximum inflatables
for 20 amp
Circuit
(80% usage)
inflatable (typical 4′) 52 0.43 27 36
inflatable (typical 6′) 58 0.48 24 32
inflatable (typical 8′) 80 0.66 18 24
inflatable (typical 12′) 86 0.71 16 22

 

Rule of Threes for Incandescents: On just about every string of Christmas lights you buy before 2008 (especially incandescent lights,) it will have a sticker saying to never plug more than three of them together in series. Don’t try and bend the rules by sneaking in an extra string or two. The wires powering those little lights are small and not designed to handle a lot of electrical current. Violating the rule of three’s will get you blown fuses, melted wire or a fire.

Plugging Plugs into Plugs and the Rule of Threes: You can always plug the plugs into the top of other plugs. Theoretically there is no limit other than the total amount of current being supplied… but it’s good practice to stick to the rule of threes… no more than three plugs plugged on top of each other and never connect more than three incandescent strings in series.

Always be on your toes when working with electricity. Why? The stuff really can kill you.

If you have any questions or concerns at all about electricity, please consult a licensed electrician

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