# All Christmas Lights on String Burned Out At Once



## Evanco (Dec 7, 2017)

So I have this Christmas tree with 2 light strings permanently attached to it. What happened was that one by one a few lights failed in short order, and then one whole string went out. I continuity checked them all and all but 2 (out of about 60 or so) were burned out, with burn marks on the interior. What I need to know is if this could have been caused by a power surge or if it is the string itself that is faulty, because I don't want to buy new bulbs only to have this happen again.


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## Macboatmaster (Jan 15, 2010)

Unworthy of the risk - presuming the tree is inside the house
My advice scrap it.

That said


Evanco said:


> What I need to know is if this could have been caused by a power surge or if it is the string itself that is faulty


have you had a power surge.
Are lights via AC and power supply of the sort that converts mains AC to 12v or whatever
If so the unit instead of producing 12V may well have gone faulty and sent far higher voltage to bulb circuit.
Without knowing what the system is no ne can advise you


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## Evanco (Dec 7, 2017)

The lights are on 120 volts. I do not know if I have had a power surge. The tree is artificial and the lights permanently attached. I suppose I could hang another string of lights on it, but I just wanted another opinion.


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## Macboatmaster (Jan 15, 2010)

So is 120 volts your AC supply as for instance in some parts of the Carribean and if so are the lights direct to that supply or after the AC plug is there some manner of power transformer
as for instance shown here
https://www.lights4fun.co.uk/i/q/PL...V6JPtCh2aggrtEAQYCiABEgKOKvD_BwE&gclsrc=aw.ds

I know you have said


Evanco said:


> but I just wanted another opinion.


but unless you can tell me how your system works even although the lights are permanently attached - it is impossible for me or anyone else to advise you.

I have some knowledge in the area of electrical work, but anything I can say without the details is really little more than a guess and therefore not a risk I would take - eg. to offer dangerous advice.


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## Evanco (Dec 7, 2017)

There is no power transformer; all it is plugged into is a surge protector.


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## Macboatmaster (Jan 15, 2010)

Unless there is some circuit inside part of the tree - other than the wiring for the actual lights, that changes the mains 120 to 12v or whatever - if these are not leds but incandescent bulbs, then my guess is that either the wires have developed a short circuit when unfolding the branches OR from the link below
https://www.quora.com/Christmas-tre...-no-longer-are-What-issues-led-this-to-change
When all the bulbs are working, the voltage drop across each bulb is small, usually less than about 5 V (up to 12 V in a 10-light string, in the U.S.). But when a bulb burns out, the full 120 V (or 230 V, elsewhere in the world) is applied across its contact wires. (Why? Because there is no voltage drop in the remaining bulbs, since there is no current.) The high voltage burns through the insulation on the shunt wire, making it conductive and bypassing the burned-out bulb.

I think the latter is the likely and I go back to what I said at the start - with 58 gone and the obvious high voltage delivered to cause the `burn marks` it is time to forget those lights - the risk of you seriously injuring yourself or a fire is to great


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## Evanco (Dec 7, 2017)

Macboatmaster said:


> Unless there is some circuit inside part of the tree - other than the wiring for the actual lights, that changes the mains 120 to 12v or whatever - if these are not leds but incandescent bulbs, then my guess is that either the wires have developed a short circuit when unfolding the branches OR from the link below
> https://www.quora.com/Christmas-tre...-no-longer-are-What-issues-led-this-to-change
> When all the bulbs are working, the voltage drop across each bulb is small, usually less than about 5 V (up to 12 V in a 10-light string, in the U.S.). But when a bulb burns out, the full 120 V (or 230 V, elsewhere in the world) is applied across its contact wires. (Why? Because there is no voltage drop in the remaining bulbs, since there is no current.) The high voltage burns through the insulation on the shunt wire, making it conductive and bypassing the burned-out bulb.
> 
> I think the latter is the likely and I go back to what I said at the start - with 58 gone and the obvious high voltage delivered to cause the `burn marks` it is time to forget those lights - the risk of you seriously injuring yourself or a fire is to great


Good idea; I will just get me another light string. Marking this as 'solved'.


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## Evanco (Dec 7, 2017)

An update to this: the _second _string of lights is now burned out. They just suddenly went dead, and they are scorched inside just like the first one. The first string was plugged into the back of the second string, so I don't know why it went out. I sure hope it ain't the extension cable that it is plugged in to, although it shouldn't be since the other devices plugged in to the extension cable are working fine. Definitely marking this one 'Unsolved' again, because now I should worry.


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