# Christmas lighting problem **URL:** \ **Category:** Factual Questions\ **Created:** [December 17, 2004, 7:12pm UTC](https://boards.straightdope.com/t/christmas-lighting-problem/280398 "2004-12-17T19:12:37Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [December 17, 2004, 7:12pm UTC](https://boards.straightdope.com/t/christmas-lighting-problem/280398/1 "2004-12-17T19:12:37Z")
Well, this is embarrassing, since I’m an electrician by trade. I’m having a problem with a string of outdoor lights that I’m hoping someone can figure out for me. Here’s the setup: I have about six or seven strings of lights on an outdoor tree. These are the miniature type, non-flashing, all identical and from the same manufacturer, two-wire strings. If one bulb burns out, all others stay lit (according to the package). One of the strings that is located in the middle is the problem child. Only half of it is lit, and it’s the half on the power side of the string. In other words, there is darkness from the male end to about halfway up the string, then the rest is lighted, and all the strings downstream from this one are lighted, as are all strings upstream. For the life of me, I can’t figure out how this can happen, and don’t know how to fix it. Any help to solve the mystery appreciated. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [December 17, 2004, 7:17pm UTC](https://boards.straightdope.com/t/christmas-lighting-problem/280398/2 "2004-12-17T19:17:07Z")
That set has a bad connection/loose bulb (one of the bulbs that is out). You need to pull each one and replace it firmly with an extra bulb that you just move socket to socket. So, grab an extra bulb, and pull one out bulb and replace with the working bulb or buy a xmas bulb tester tester or go to the plug end and and slide open the **tiny fuse box** on the strands plug end. Common ones have **two** fuses…one each for the dual strand of lights you describe. One might be blown — especially if you have seven strands connected in-line!! ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [December 17, 2004, 7:36pm UTC](https://boards.straightdope.com/t/christmas-lighting-problem/280398/3 "2004-12-17T19:36:45Z")
> [@Philster](#): > > go to the plug end and and slide open the **tiny fuse box** on the strands plug end. Common ones have **two** fuses…one each for the dual strand of lights you describe. One might be blown — especially if you have seven strands connected in-line!! :smack: What a total brain fart on my part! I wasn’t thinking about the bulbs being on two different lines. I’ll check the fuses. By the way, it can’t be a bulb problem (see OP). ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [December 17, 2004, 7:51pm UTC](https://boards.straightdope.com/t/christmas-lighting-problem/280398/4 "2004-12-17T19:51:52Z")
It can be a bulb problem. Take a bulb out and see how much of a probelm that is. So, while all the bulbs look like they are in their little ol’ sockets, the tiny wires each bulb has must make contact with the bulb socket. The test bulb allows you to pinpoint the problem, because those little bulbs have tiny wires, and if one is broekn, the circuit is broken. If you don’t have a test bulb/spare, scavenge one from further down on one of the other strands. ---
**Author:** ![FatBaldGuy](https://avatars.discourse-cdn.com/v4/letter/f/ecd19e/32.png) [@FatBaldGuy](https://boards.straightdope.com/u/FatBaldGuy)\ **Post date:** [December 17, 2004, 7:53pm UTC](https://boards.straightdope.com/t/christmas-lighting-problem/280398/5 "2004-12-17T19:53:17Z")
> [@Chefguy](#): > > By the way, it can’t be a bulb problem (see OP). Yes, it can. Even on the type where the rest stay lit if one burns out, a loose connection can hose the whole string. ---
**Author:** ![Cheesesteak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cheesesteak/32/3694_2.png) [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)\ **Post date:** [December 17, 2004, 8:23pm UTC](https://boards.straightdope.com/t/christmas-lighting-problem/280398/6 "2004-12-17T20:23:35Z")
Just for a bit of background [how xmas lights work](http://people.howstuffworks.com/christmas-lights2.htm) . It has a diagram showing how part of a set of lights can go out via a bulb problem, though it takes 3 wires instead of two… You would have 2 sets of 50 bulbs running parallel in a single strand. Fun info on that page showing how the bulb shunt provides protection against the whole string going out. Note that the shunts aren’t 100% effective, I’ve seen tools designed to fix strings by forcing the shunts to connect properly, a broken shunt is just as bad as a broken bulb. As a result, these protected strings can still actually go out via a blown out bulb. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [December 17, 2004, 9:09pm UTC](https://boards.straightdope.com/t/christmas-lighting-problem/280398/7 "2004-12-17T21:09:16Z")
_::much waiting as Chef pulls every light::_ Ho Ho Ho! 😛 ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [December 17, 2004, 11:45pm UTC](https://boards.straightdope.com/t/christmas-lighting-problem/280398/8 "2004-12-17T23:45:45Z")
> [@Philster](#): > > _::much waiting as Chef pulls every light::_ > > Ho > > Ho > > Ho! > > 😛 If it isn’t a fuse, then I think I’ll just suffer through with that half string out; it’s too damn cold to fuss around out there. ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [December 17, 2004, 11:49pm UTC](https://boards.straightdope.com/t/christmas-lighting-problem/280398/9 "2004-12-17T23:49:36Z")
This thread is an embarassing reminder of how long it’s been since I worked in the field. Crap. ☹ ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [December 22, 2004, 5:10pm UTC](https://boards.straightdope.com/t/christmas-lighting-problem/280398/10 "2004-12-22T17:10:25Z")
From **Cheesesteak** ’s link: > [@](#): > > If you look closely at a bulb, you can see the shunt wire wrapped around the two posts inside the bulb. The shunt wire contains a coating that gives it fairly high resistance until the filament fails. At that point, heat caused by current flowing through the shunt burns off the coating and reduces the shunt’s resistance. (A typical bulb has a resistance of 7 to 8 ohms through the filament and 2 to 3 ohms through the shunt once the coating burns off.) I don’t see how simply removing a material coating could lower the resistance of the shunt at 60 Hz. There must be something more complicated going on. Anyone know what it is? ---
**Author:** ![picunurse](https://avatars.discourse-cdn.com/v4/letter/p/7bcc69/32.png) [@picunurse](https://boards.straightdope.com/u/picunurse)\ **Post date:** [December 22, 2004, 10:13pm UTC](https://boards.straightdope.com/t/christmas-lighting-problem/280398/11 "2004-12-22T22:13:02Z")
> [@Chefguy](#): > > If it isn’t a fuse, then I think I’ll just suffer through with that half string out; it’s too damn cold to fuss around out there. Just remember to throw it away, and get a new set after Christmas for cheap/