How Many String Lights Can I Connect Together?

How Many string lights can I connect together?

String lights have been part and parcel of any decorative occasion for a long time. This low-imitating light looks like faraway stars sitting on your backyard tree or gazebo. While they are fun and mesmerizing to look at, their installation might be confusing sometimes. You never know how many to string together for one outlet or whether they’re safe to plug into an extension cord. This can quickly become overwhelming if you start to think about it.

But you can make this irritating matter a simple and plain one by applying some easy tactics. If you are wondering what those are, then you need to read the content till the end. All you need is some required data on your string lights, your house’s electricity setup, and some basic math calculations. Read thoroughly to figure out how many strings you can connect together and the factors behind calculating the math. Additionally, you will find answers to what happens if you connect too many lights, along with some important disclaimers.

Factors Behind Connecting String Lights Together

Factors behind connecting string lights together
Factors Behind Connecting String Lights Together

1. Light Types

Not all string lights are made equally. Different light types have different power consumption capacities. The most common and favorite string lights are incandescent and LED ones. While incandescent lights are widely used as string lights, recent rope-like LED lights have seen similar use. Incandescent lights use a manual filament ignition to create light. Whereas LED lights use a pack of LEDs attached to a circuit to imitate lights.

Incandescent lights require a higher amount of electricity to burn their filaments. A strand of such light can consist of 20 to 100 pieces of bulbs and consume 5 to 100 watts (based on the number of bulbs in the strand) of electricity. On the other hand, a strand of 70 LED ring lights will consume an average of 4.8 watts in total.

2. Circuits Capacity

Circuits are everywhere in the electrical world. From your mobile phone to your household main board, they form the backbone of any electrical line. In your house, there are different circuits to run different electrical operations. A strand of string light will rely on these circuits to provide them with crucial electricity. At the same time, a chain of string light is nothing but also a formation of circuits.

The load of the lights determines how many you can have. Most of the household in the USA has 15A or 20A capacity circuits.  A regular 15amp circuit can have up to 1400W of lights connected, or one 1400W light or 14*100W light bulb.

3. Cords Specifications

Just like circuits, the specifications of the cords are also crucial to determining how many string lights you can connect together. The maximum connectivity for pre-wired light strings (mini lights, craft lights, and LED Christmas lights) is based on the UL (Underwriter’s Laboratory) maximum connection guideline of 210 watts. The number of watts that one cord can handle is measured by dividing 210 watts by the total watts required by the light string.

To give you an example, suppose one cord is rated at 20 watts. So you can have 210/20=10.5 or 10 strings. If you have a string full of light that has 20 watts of power consumption, you can add 10 such strings, one end joined by another, until it exceeds 210 watts.

Measuring Number of Light or Amount of Electricity Needed

Measuring number of light or amount of electricity needed
Measuring Number of Light or Amount of Electricity Needed

You have to do some simple math to determine the possible number of lights or the amount of electricity needed. Note that, a string of 100 incandescent lights can consume 0.1kWh per hour or approximately 100 watts. Now you have to consider this number with your house’s electrical circuit capacity. Generally, most USA houses have 15 or 20-amp capacity circuits. Each of these amps is equivalent to 120 volts. You can convert this number in watts by multiplying the number of amps with 120 volts. So the math goes as:

  • For 15amp circuit- 15*120= 1,800 watts
  • For 20amp circuit- 20*120= 2,400 watts

But one important thing to note here is, that all the possible electrical elements attached to one circuit must not consume 80% of electricity against each circuit. This is suggested by professional electricians for the safety of that electric circuit and the electrical elements attached to it. That means we have to reduce our previous finding of watts per circuit to 80%. You can use a simple formula of ‘80%*(Amps) = Watts/Volts’ to calculate the actual useable electricity. This will be:

  • For 15amp circuit- 80% of 15*120= 1,440 watts
  • For 20amp circuit- 80% of 20*120= 1,920 watts

Now, to find a tentative number of lights, we have to divide these final results by the electricity consumption of each string of lights. If one strand of string light uses 100 watts per hour that means,

  • For a 15amp circuit- 1,440 watts/100 14.4 strings or 1440 lights.
  • For a 20amp circuit- 1,920 watts/100= 19.2 strings or 1920 lights.

This calculation shows you can attach a maximum of 14 string ends against a 15-amp circuit and 19 strings against a 20-amp circuit. Now comes the UL (Underwriter’s Laboratory) tag, which shows a maximum of 210 watts can be mounted in a single series. This means if you are using a string of 100 bulbs worth 100 watts, then you can string a maximum of 2.1 strings or 210 lights end to end. So you have to divide the series in pairs while attaching it to the circuit.

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What If You Connect More String Lights Then Capacity?

What if you connect more string lights then capacity?
What If You Connect More String Lights Then Capacity?

After seeing all of these calculations, you may be wondering what happens if I connect more string lights than the circuit or cord capacity. No worries! You are living in the modern era, and almost all the house’s electric mainboards are equipped with modern circuit breakers. They are configured to react by shutting down automatically if power consumption crosses that circuit’s safe passing limits. meaning that if you connect more string lights than the circuit’s capacity, i.e., 2000 watts against a 15-amp circuit, it will instantly shut itself down.

You may have faced a similar sudden partial electricity shutdown in your house. This is due to the exact reason elaborated above. To restore the electricity, you had to unplug some of the electrical elements from the board and switch that circuit back online again.

Odds Of Accidents: Some exceptional cases can also lead to unwanted scenarios, such as when your circuit can perish permanently and needs to be replaced with a modern one. With sudden ups and downs in electricity voltage, some lights can burst out, and lastly, electrical cords holding the lights can burn out. However, due to the safety measures considered for making these components, the chances of these accidents happening are slim. These happen mostly because those components or cords were faulty or unsuitable for use and caused a bottleneck in the system.

Disclaimer for Connecting String Lights

As with anything, I would like to put out some disclaimers regarding connecting string lights together:

  • Disclaimer 1: The circuit used for plugging string lights should be dedicated to housing string lights only. Any other electrical element attached to that circuit will reduce the available electricity for the string lights. For that, you can use other electrical elements, for sure, but make sure you have the correct calculation on the total wattage you are using in that circuit.
  • Disclaimer 2: Another important thing to consider here is that these figures are based on basic calculations and don’t guarantee that they will be the exact number for your house. There can be slight deviations in terms of your house’s electricity load, grid electricity supply voltage, etc. that are constantly variable. So, attach string lights with caution and as per a professional’s suggestion.
  • Disclaimer 3: The number of lights you can connect together is variable depending on the electric consumption each light causes. If the lights are more energy efficient, you will be able to connect comparably more string lights together.


1. Why does the fuse keep blowing on string lights?

The reason your electrical fuse keeps blowing on string lights is likely because of overloading or short circuits. Check if the wattage you use on string lights exceeds the circuit’s capacity first. You need to check the wiring thoroughly to see if there are any defects or exposed wires that are causing short circuits.

2. Can you connect LEDs and string lights together?

The most likely answer is no; you can’t connect LEDs and string lights together. Because LED and string lights are built differently, String lights use a higher amount of electricity than LEDs. If you do attach them together, the high draw of electricity to the string lights will likely blow the LED lights fuse first and similarly damage the string lights afterward.

3. How do you tell if a fuse in a string of lights is bad?

To tell if a fuse in a string of lights is bad, you need to physically inspect the fuse. For that, remove the fuses carefully and place them against a brighter background. If the fuse is good, you will be able to see an intake string attached between the two metal ends of the wire. A broken or shattered string will be considered a bad fuse.

Final Thoughts

To conclude here, a lot of people get confused when it comes to how many string lights can be connected together. To sort out your confusion and query, you have to consider three factors: the type of light you are using, your house’s electrical circuit capacity, and the cord’s capacity for carrying electricity. Most users like to use small incandescent string lights. They come in wide ranges and consume more energy than LED lights. Next, your house and the light cords are configured to maintain a particular amount of electricity portability. All you need is to read the lights user manual, grab a calculator, and do some basic math to figure out how many string lights you can connect together.

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I am Donald M. Beyer and I am backyard enthusiasts. I am a homeowner who has been doing DIY projects in and out of my house for many years. From simple backyard lunches to making an old-school pizza oven in my own backyard, I have a lot of experience in turning my backyard into my and my family’s personal playground.

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