No, you can’t lengthen or shorten standard series-wired incandescent and LED Christmas tree light strings that are made with 2 or 3-wire harnesses. Even if they work at first, they won’t last long. If, however, you are installing C7/C9 18 AWG Christmas light cords with sockets and screw in bulbs that are wired in parallel, yes, you can shorten them.
For a full explanation of series and parallel wiring, look at the post: Are Christmas lights wired in series or parallel?
Mini Christmas Tree lights and Pre-wired LED light strings
These light strings have smaller bases, are made with smaller gauge wire and are wired in series.
Incandescent mini light strings are like these.
LED strings are like these.
We know you’ve seen those videos on the web showing how you can lengthen or shorten these light strings but the fact is that either more or less current will flow through a different number of bulbs than the lights were specified for and this means you’ll run into one of the two following scenarios:
- light strings will either burn too bright and burn out in a short perior of time
- light strings will be dim, won’t match other lights in the installation and will be generally disappointing
For ultra-low current LED sets, the investment, especially, isn’t worth the risk.
What am I supposed to do?
Unfortunately, there isn’t too much that can be done at the end of a run if there are a few leftover inches/feet of Christmas light strings. Wind them up, secure the coil with electrical tape and tuck the rest of the light string out of the way. Wire ties can be handy at times like this.
Jumping between windows?
Visually disguise the bulbs that are messing with your perfect rectangular window vibe but hiding them with a couple of quick turns of electrical tape.
18-AWG Cords and Bulbs
Cords and bulbs wired in parallel have the advantage that their constant voltage, varying current configuration allows them to be trimmed to fit.
These are light cords and bulbs like those shown in these categories.
Work with a Master Electrician and clip your string to fit using proper termination.
Proper termination can include:
- installing a female Gilbert plug on the end of the wire
- dipping the end in a product type referred to in the field as “liquid electrical tape”
- wrapping the end of the cord with electrical tape
The best help you can find with this is counting on the professional assistance of an electrician.
You say you cant cut mini lights that are in series, but what about cutting them at the point where they go down to 2 wires and are parallel at that point? When one light bulb goes out in a standard set of mini lights you usually loose half the string. But the other half doesn’t brighter when this happens right? Would the spot in between the two series sections be an acceptable place to cut?
In mini light strings where one half or a third goes down, they are wired in 2 or 3 independent circuits so you don’t see a change in their appearance when the other half is down.
If half the set is out and it is not an issue with an unseated or broken bulb, it would be safer and more electrically sound not to cut the string in half but to retire the set. You might be able to use the bulbs as replacement bulbs in other identical sets that are still fully functional.
I have a set of lights 10meters long with a bulb every 1meter. They are all in series – two wires from the male end three the rest of the way until the end where it goes back to two for the female plug.
I want to split the set, add new male and female respectively and put an extension piece in middle and then reintroduce the 2nd half of the set (6meters lights, 2 meter blanking cable, 4meters lights). Is this possible and as I’m still using the 10 bulbs in the sequence (albeit with an extension in between) will they be OK re: resistance?
The transformer is capable of taking 700m of these lights in sequence- not sure if that makes a difference.
Thanks for your help
We would strongly suggest you not splice in that line of cord and alter the resistance of the set. We have seen this permanently disable a set of LED lights. Your best option would be to add a second set of lights and visually hide them in the gap.
If I used a c9 or c7 led string set and let’s say the last 5 bulbs ends at my corner gutter and the want to go straight up 9 ft to my 2nd floor gutter and I cut the wires and splice in new wire to elongate the space in between to custom fit my lights to the house but keep the number of lights per string the same to not change the wattage and such of the light string and then continue to connect strings together….can I pretty much do that to a string of lights and pretty much Add wire to extend extend wires in between lights to achieve custom lengths to my house
First, you would need to use a traditional C7 or C9 bulb and cord configuration like the items in this category: C7 or C9 Bulbs and Cords instead of pre-wired strings. Yes, using proper electrical practices, you can splice into this kind of cord with a piece of bulk wire. Be sure to take a look at this category of gilbert plugs to make your life easier.
We also suggest that you have an electrician swing by and check out your work or have one take care of it for you.
Hope that helps.
I purchased a string of solar powered Edison style LED patio lights that are dimmable, can change color and can be turned on and off by remote control. There is also female plug at the end to add a second string if needed. Two wire, one white, one black. The string was longer for my purpose so cut the cord 4 bulbs short to fir our pergola. All fine but last bulb would not light. To test if my actions caused this problem, I rewired the end cord. They would not light either. So it appears perhaps my cutting had nothing to do with last 5 bulbs not lighting? An no, I did not test lights prior to installing them.
That’s a tricky issue. You are experiencing first hand how modifying low-current light strings can sometimes be problematic. (But since we don’t know if they came on before, It is uncertain.) There could be an issue with transformers or filters in any kind of controller that have been bypassed.
Are the bulbs removable? You might consider switching out that last bulb just in case it is the bulb itself and not the wiring.
Cutting off those last 5 bulbs could have unfortunately affected the entire string. Try switching out that last bulb to see if it helps, otherwise, you may need to start over with a new set. Look for a light string that is wired in parallel instead of series if you want to adjust the length of the cord. The only issue there is that you would more than likely not have the cool control features.
Hope we’ve helped a little.
I have a number of 25 C7 light strings that I use in my display. To more customize the length of some of my strings, can I safely shorten the string by cutting them from the plug end and just taping the cord end?
If they are 18 AWG parallel wired cords, you can cut them and terminate the ends with electrical tape.