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Christmas Light Troubleshooting

What is Christmas without Christmas lights?  If you take a drive around most neighborhoods this time of year you will see light displays that range from the minimal to the mind blowing.   However, after putting in all of the effort for just the perfect display, some of you may have experienced the frustration of discovering a string of lights that suddenly quits working.  In this article, I discuss some of the reasons for this to occur, and how you troubleshoot the problem.

So you have your lights all installed, and they were working just fine, but then you notice that the entire string plugged into a particular outdoor circuit are no longer working.  The first thing to check is the circuit breaker that feeds that outlet.  Check to see if it has tripped.  Here is a helpful post from our website regarding circuit breakers, and how to reset a tripped breaker.

If you are sure the breaker is okay, and you still don’t have lights, then check any of the outdoor receptacles on that circuit to see if one of them is a GFCI receptacle with the test / reset button on it.

Push the test button to see if it trips.  If nothing happens, then try the reset and test again.  If you hear the receptacle trip after the reset, then that was likely the problem, and just reset it and again check to see if your lights now are working.

If they are, that’s great, but you should investigate as to what may have caused the problem.  It could be that moisture (wet snow, ice, or rain) has caused the issue.  It would likely be at a connection point at the source, or on one of the light strings.  Take appropriate measures to correct the problem so it doesn’t happen again.

If everything with the circuit seems okay, yet still no lights, then check to see if you have power at the receptacle in question.  If you have an electrical meter or voltage tester, use that.  If not, then just take a lamp or radio, or something that you know works, and plug it into that outlet.  If it works, then you have a problem with the light string.

Most of the new light sets out now have built in fuses to protect overloading of the light string itself.  Remember that if you use the light strings to feed through to one another, all the current in all the strings is passing through the original connection to the outlet.  All light strings that you use should be approved for the use, and have a UL or equivalent approval sticker or tag attached to it.  Read all warnings and instructions that come with the light sets.  Here is a typical UL approval sticker attached to my light sets.

UL Label

Here is the label that is also attached to the light string itself.

Christmas Light Label

It says:

“CAUTION:  1. For temporary 90 days max installation and use only.  2. For indoor and outdoor use.  3. To reduce the likelihood of excessive heat and possible damage, use only decorative lamp accessories packaged with this product.  4. Always unplug this product before installing or replacing fuses and / or lamps.  5. Replace lamps only with 3.3 Volt, .066 Watt spare lamps provided with this product.  6. This is an electric and not a toy! To reduce risk of fire, burns, personal injury and electric shock it should not be played with or placed where small children can reach it.  7. DO NOT OPERATE WITH BULBS MISSING FROM SOCKETS. MISSING BULBS SHOULD BE REPLACED PROMPTLY.

E246482  Model CLED-5.5MM-100a   120V, 60Hz, 0.067A,  8.0W.  0611  Made in China.

This device complies with Part 15 of the FCC Rules.  Operation is subject to the following two conditions: (1) this device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation. ”

So if the outlet is working, and the lights are not, then the problem is likely that you connected too many lights together, thus overloading the rating of the light string.

On this particular set, the fuses are located inside the plug assembly.


Plug Opened

You need to extract each of these fuses and check to see if they are burnt out.  You may find that only one fuse inside the plug.

Prying out fuse

These fuses are very tiny, and good luck finding a replacement if you lost the ones that you got when you purchased the lights.  A well-stocked electronics store is probably the best option.

Using a voltmeter, you can check to see if the fuse is blown, or just try replacing it with a new fuse to see if this fixes your problem. Here’s how you test a fuse using a DVM (digital volt meter).

The meter should show very little resistance, in this case 6 ohms.

Testing fuse

Testing fuse meter reading

If the fuse is blown, the meter will show the same reading as it would if the meter leads were not touching anything.

Meter open circuit

If you find that a fuse is blown, you probably have too many light strings connected together, and need to re-think how you are going to power your light strings.  With these light strings, the maximum load for connecting multiple strings of lights together is 1.75A, 210W.  Given that each string is rated at 8W, .067A, than you could connect 25 or 26 strings together using the feed through connections.

Label max loading

Armed with this information you should have your Christmas display up and dazzling the neighbors and family in no time!

Remember – safety first!  This is particularly true at the Christmas Season.

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