This is a pretty popular question when it comes to Christmas lights. The answer is simple but simultaneously complicated.
Here are a few guidelines but for all things electrical, consult with a master electrician when making decisions about your project.
How many bulbs or strings you can run in series depends on:
1. Answer based on your light string or bulb/cord specifications
Every light string on our website should have a maximum connectivity rating.
(If the item you are looking at is missing that specification, ask a question on that product and we’ll research and update that information. We carry a lot of products and every once in a while, one or two will slip past us.)
Guidelines for Mini Lights and LED Light Strings
The maximum connectivity for pre-wire light strings – mini lights, craft lights and LED Christmas lights is based on the UL (Underwriter’s Laboratory) maximum connection guideline of 210 watts.
DEFINITION: Maximum connectivity refers to the maximum number of strings you can connect end to end in a single circuit. (Or how many plugs you can stack on top of each other when you are working with craft lights.)
So, maximum connectivity is calculated by dividing 210 watts by the number of total watts required by the light string you are considering. For example if your light string is rated at 20 watts, then you can run a maximum of 10 strings together in series.
Now you can see why LED light strings can be run with so many more in series than traditional incandescent mini lights that require up to 10 more times the power to operate.
UL can change their suggested ratings and we change our specifications to reflect that.
Guidelines 18 and 20 AWG C7/C9 Bulbs and Cords Here are the basic rules about our C7/C9 cords.
1. Connect no more than two 20-AWG 25-foot cords in series in a single run.
2. Our 50 and 100-foot cords do not come with a female plug. They just have a single male plug. If you are using multiple strands, run an extension cord to the center of your project and run a 50 or 100-foot cord from the extension cord splitter. (Think of the cords making the top of a “T” and the extension cord is the vertical line.)
3. If you are using our 1000-foot spools that must be cut to fit, consult with a Master Electrician on your project. Discuss these important guidelines with him or her:
- Our maximum suggested number of traditional incandescent C7 and C9 bulbs is 200 bulbs for each style – especially if your bulbs are spaced 12 inches apart. (The wattage for our bulbs are listed in their specifications.)
- For LED bulbs the maximum number of bulbs you can run in series has less to do with the bulbs specifications and more with the light line length for 18 AWG wire which is 250 feet. This means that even if you are using a .86 watt LED bulb, you can’t run more than 250 feet of cord.
We’ve had customers call in who have received bad information and are under the impression that if they use LED bulbs then they can run 1000 feet of 18 AWG C7 or C9 stringer wire in series. THIS IS AN ELECTRICAL HAZARD. The wire itself will become a fuse and is a fire risk.
That’s the biggest advantage to pre-wired LED strings is that you can run 20-88 strings of lights in series. But that’s on 20-22 AWG wire with 3-wire engineering. Totally different lighting.
(I just can’t tell you how this makes me put my head in my hands and why we’re continuing our commitment not to ship your customer service calls to a random third party call center. You may have to leave a voice message but you won’t receive information like that!)
Again, take time and spend $100-150 for an hour of an electrician’s time to make sure your custom work is electrically correct.
2. Answer based on the electrical service you are plugging them into.
As we mentioned above, keep track of the total number of runs of lights or cords/bulbs as you are splitting them off of your extension cords and splitters and take care not to exceed 85% of the wattage of your breaker. For a common household breaker, use a rule-of-thumb not to exceed 1400 watts per plug.
If you have a larger breaker and have verified that your NuWave Oven or your Microwave isn’t on the same circuit and electrician might tell you that you can work with a different number but we like to be safer than sorry.
By the way, that doesn’t mean per outlet but per breaker. <smile> You may have multiple outlets on a single breaker so be sure to keep track. Again, better to shoot for a lower number than risk maxing out your breaker.
Speaking of outlets….
We suggest that you connect all of your Christmas lights into GFCI rated outlets when using them out of doors.
And a word about surge protection….
We also highly recommend that you use an outdoor rated surge protector – they make these with built in timers – for your outdoor installations. LED lights are made of diodes that are like the components of your computer. In the same way that you would never plug a computer straight into a wall outlet, protect your LED lights from surges on the line and use a surge protector.
A standard surge protector (like the one you use for your computer) is fine for indoor usage.
As a random side note – which I’m rather famous for in my circle of friends – I learned from a retired New York state code inspector that the closer you are to hydroelectric power, then the more surges will appear on your line.
So all you folks who use power generated by Niagara Falls or other hydroelectric facilities would be doubly wise to use surge protectors for your Christmas light display and save yourself the heartbreak of seeing your sets take a hit.
Who knew?
Any stories? Share them in the comments. 🙂
Pin this image for later!
It is still generally safe and dependable to stick to the three-strand recommendation from the original UL recommendations. With LED lights, you may now utilize more than 10, even up to 50 light strands
The 3-string rule, as a rule of thumb, works for most glass light strings. For 25-foot 20 AWG cords, the specification is just 2.
Using 210 watts as the maximum run for glass or LED light sets is the best measure to use if you know the wattage specification of the light strings. Some LED strings are just 2.4 watts per set so can run up to 87 strings in series.
Hope that helps.
Great question. Thanks!
I have purchased two of your 100′ C9 strings. Since you say you can run a maximum of 200 lights in a line, could I modify the end of one string with a female plug and plug the 2nd cord into the 1st?
Yes, you can install a female plug and run them together. Keep an eye on the specifications of the bulbs used to make sure you don’t exceed 10 amps.
Great question, thanks for asking.
How many C9 Christmas lights can I string together?
That all depends on the electrical specifications of the wire and the bulbs or light sets.
Sorry that we can’t give out specific electrical advice. Check the specifications of the products you are working with.
Just a heads up…a good electrician costs more than $50/hr. Our rates start at $125, like most other reputable firms—in CA at least.
I only bring this up because I would be suspect of the qualifications of any electrician charging $50/hr.
Good catch. I dropped a “1”. I’ve updated that figure to a realistic range.
Does the way you connect your lights matter (e.g., end-to-end vs. all the plugs into each other, say, at the bottom of your tree/bush)? Thanks!
We call plugging the plugs into each other “stacked” or “stacking”.
And yes, you’ve asked a great question, that does matter. The maximum number of plugs/sets that you can connect via stacking is the same as if you were plugging them end to end.
So, you can’t stack more than the same number of strings that are the maximum for end-to-end installation.
For example, if you can connect 5 strings of 100-bulb mini lights in series, you can only stack 5 plugs. For nets or strings, check the tag next to the plug or the product specifications to see what that number is for each set as it can change based on several variables.
Hope that helps!
I have a tree that needs 10 strings of mini light strings rated at 40 watts. The product says a max of 5 sets. If I use a 3 way splitter on a outdoor electrical cord, would I be okay with the 10 strings on one run?
No, you cannot run them all together in one run of 10 strings.
You have to follow the product specifications and connect only 5 sets end to end. You could power 10 sets in 2 separate lines/circuits connected to a medium-duty extension cord and splitter. In other words, 5 strings in one direction from the splitter, and another 5 strings powered by another female “outlet” on the splitter in a different direction.
If you have any specific questions or concerns, please have an electrician take a quick look at your installation.
If I plugged in more than 10 sets and they all went out, I removed the extra but they are still out. Is there any way of fixing this?
More than likely, you blew a fuse in one or more of them.
Make a visual inspection of the sets to see if any of the bulbs are “smoked”. If you do not see evidence of physical damage, start checking the fuses that are located in the male plugs. One or more of them are more than likely blown.
Slide back the little door, and see if the filament in the fuse is burned up. (Like a light bulb filament when a bulb goes out.) Replacing any blown fuses should fix the problem. If not, there may have been some damage to the wiring harness(es).
Work through the sets one by one before plugging them in again in series.
Hope this helps! Good luck getting those lights up and running again.
Shellie
I have a double power plug under the front Eve’s of my house. My icicle lights are rated at 72 watts a set so I can only connect three sets together. Can I connect three sets to both plugs?
Yes, you can plug three sets into the outlet, and then the remaining other three sets into the same outlet as long as the total wattage of all devices plugged into the circuit breaker associated with that outlet isn’t more than 1000 watts (for a standard household breaker).
If in doubt, ask a master electrician to take a look at your project.
Hope that helps!
Merry Christmas, I have two strings of rice lights and 2 strings of the regular little pointy bulbs. Can I run all four together safely on my indoor Christmas tree?
Thank you, Peggy
Hi Peggy,
I would not run the rice lights and the regular lights in series as they more than likely have significantly different electrical specifications. Keep the different styles of lights plugged in separate circuits (not into each other).
I would be most concerned that the rice lights are LED and a higher current draw created by running the sets in series could instantly damage them.
Great article. thank you. very insightful./
Am I misreading my tag, or do my lights have 61.2 volts? Is that even possible?
Hey Julia, that is a weird spec!! Is that volts or possibly watts? Do they have a standard male plug?
You’ve given me soemthing to think about!!
Shellie
How many strings of electrical lights powered by fuses can you have without effecting the lights and stop them from lighting up.??
That depends on the style of the light string – how many bulbs, how many watts they are rated at.
Check the tags near the bases of the light strings and use the UL specification there to determine the max number of strings you can run in series. The current UL spec is 210 watts max.
Hope that helps!
I have 6 strands of single bulb LED icicle lights hooked together. I have 1st, 3rd and 6th stand working, 2nd, 3rd and 4th are out. Where do you suggest I start to look first? Thanks
Pull the non-working strings and plug them into a separate outlet one by one as a place to start to see if the issue is in the plug of the light string before it. Then check the fuses and replace them if necessary. That’s about as much as you can do with most sets of LED icicle lights. Be sure to plug your LED lights into surge protectors.
I have regular “old style” mini lights on the same string as my new LED C9’s. About 5 strings altogether, 2 LED C-9’s and 3 100ct Mini’s. They work for about 5 minutes and then they all go out. I remove the string of mini’s closest to the power source and they work for 5 minutes again and they kapow again. Rather than go thru this litany for all the strings and I to conclude that I cannot connect LED C-9’s on the same string-to-string as old style mini’s?
Sorry for my slow response but that is exactly right — you cannot mix LED and traditional lights in the same series circuit since glass, incandescent light strings pull MUCH more current than your LED sets. Split them into separate circuits after you replace any fuses if necessary. We suggest that you even keep LED lights from different manufacturers or styles on separate circuits since they don’t necessarily have the same specifications even though they are low amperage.
I have a question. So the article states that I shouldn’t go further than 250 feet of stringer with LED bulbs, but does that stand true if there are several splices in the wire in order to catch peaks? If not how many splices are allowed in a run?
Yes, you’ll need to keep a close eye on that max length for 18 AWG wire. The best thing to do is to have a master electrical check out and work with you on your installation.
(I think I understand your question correctly – let us know if you have other questions.)
That would include splices, the total combined length cannot be more than 250′. Example: Your main line is 50′ and five branches of 10′ each, the total length of the string is 100′
How many 15ft icicle strings can you put together
Sorry for my slow response. For a set of traditional incandescent icicle lights our sets can be run 3 sets in series. Thanks for your question.