How To Calculate Max Christmas Light Runs | 1000Bulbs

Not sure how many Christmas C7 & C9 bulbs you can use on a single circuit? Watch this video to learn how to calculate calculate the maximum runs of light you can use based on your wattage.

*Chapters:*
00:00 - Intro
01:00 - Why Knowing the Max Run is Important
01:00 - First Equation: Determining Usable Watts
02:06 - Second Equation: Determining Number of Bulbs
03:13 - Wiring Warning

*Transcript:*
With the holiday season quickly approaching, now is the time to start getting your holiday lighting ready. One of the most important steps to planning any holiday light setup is knowing how many lights can be used on a single circuit. The answer will largely depend on the amperage of your circuit and the wattage of the bulbs you choose. We've put together this video to help show you how to calculate the maximum runs of light you can use, based on your wattage.

C7 and C9 bulbs are the most common and well-known Christmas lights available. They're used for roof lines, windows, driveways, and everything in between. And when they are paired with commercial stringers and spools, you can build large, beautiful runs of light. However, when too many sets are connected together, you run the risk of blowing built-in fuses, overheating the wire, and even tripping your circuits.

To help prevent these catastrophes and properly determine how many C7 or C9 bulbs your circuit can handle, you will need two equations. This first equation will help you determine how many usable watts you have. That equation is:

*Voltage x Amperage = Total Watts x 0.8 = Usable Watts*

The average voltage in American homes is 120 volts. To find your amperage, you will have to check your circuit breaker box. Most US homes use 15 or 20-amp circuits. Multiply these two values together for the total watts, or the the amount of power you have available. For example, if you have a 15-amp circuit, your equation would be: *120 Volts x 15 Amps = 1,800 Total Watts*.

Since Christmas lights draw a continuous load of power, you should only use 80% of the available power to ensure safe usage. Therefore you take the total wattage and multiply that by 0.8 to find the number of usable watts. In this case: *1,800 Watts x 0.8 x 1,440 Usable Watts*.

Now that you have the usable watts, you can determine how many bulbs you can use with this second equation:

Usable Watts / Single Lamp Wattage = Total Number of Lamps.

Take 1,440 and divide it by the bulb wattage. The bulb wattage will vary depending on what you choose. The bulbs we offer at 1000Bulbs are: incandescent C7s which use a approximately 5 watts, incandescent C9s at approximately 7 watts, LED VividCore C7s and C9s, which use approximately 0.5 watts, and LED VividCore Premium C7s and C9s which use approximately 0.74 watts.

Let's say you want to use incandescent C9s. Due to their wattage, you would only be able to use 205 bulbs. However, if you chose LED VividCore Premium C9 bulbs instead, you could safely use 1,945 bulbs. LED bulbs are definitely the better choice for having more bulbs per circuit due to their lower wattage.

Before you start, please note that these equations only work for copper wired circuits. If your home or business was wired before 1970, they most likely use aluminum wiring which is unable to support the same number of bulbs. If you have any questions or need help troubleshooting issues, give us a call at 855-948-5079. Our US-based lightning experts are ready to help.


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[richardsaenz]

I'm glad to see that the video advised on continuous LOAD DUTY & to run your LOAD calculation @ 80% value.

[KevinBrumfield-rw]

This video and the solutions recommended are absolutely legit. We kept blowing breakers because of overload, using the calculations in the video we were able to get things up and running stably. Thank you all for the assist.

[AdamMarois]

Does this change at all if we attach a run mid line with a vampire plug?