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Back in the day, aluminum Christmas trees were sold with color wheels and included literature warning you not to string lights on he tree. Fast forwarded to today, I have an old aluminum tree and am still warned by people not to put lights on it. I can understand that back in the day, lights burned hotter than deep fried hell and were nowhere as safe as modern day LEDs. Is there any reason to think that I could not safely light up my aluminum tree? I feel like a string of LEDs in good repair would not pose any real risk. Thoughts?

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    I'd just earth the aluminium, myself. Or source some low voltage LED strings. – Ian Bland Dec 20 '17 at 4:07
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It isn't the heat that's the problem. The problem is the fact that those narrow strips of aluminum "needles" can work their way into a lamp socket (or the extension socket at the end) and make part or all of the tree "live" at some voltage that depends on exactly where along the string the contact occurs. AC-powered LEDs are just as dangerous in this regard as other kinds of lights.

At a minimum, ground the structure of the tree, and plug any lights into a good-quality GFCI. This should catch any single faults before they have a chance of becoming a double fault that could become a fire hazard.

Better still, just stick with the color wheel.

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    Grounding may reduce the shock hazard, but there's still a fire hazard - thin strips of aluminum can vaporize in a hot plasma flash if shorted across a high enough current, and that can lead to fires of the lights and/or decorations on the tree. If you really want lights on an aluminum tree, stick with low voltage battery operated lights. – Johnny Dec 20 '17 at 5:47
  • @Johnny: No, it's the GFCI that reduces the shock hazard -- grounding the tree helps make sure it trips as soon as the first fault occurs, before someone touches it. And the current in a string of LEDs is fairly limited to begin with -- typically a few tens of mA, which is comparable to the trip threshold of the GFCI. No "hot plasma flashes". – Dave Tweed Dec 20 '17 at 11:56
  • That depends on the LED string, I have a string of screw-in LED C9's that have 120VAC to each bulb -- it's not a serial chain of LED's. – Johnny Dec 20 '17 at 12:43
  • You had me with the hot plasma flashes. I always did think those color wheels were cool. – Paul Logan Dec 20 '17 at 15:22
  • @Johnny, that's true, but no one is putting those giant C9 bulbs on a tree. Any mini-light LED strand is going to be wired in series. – JPhi1618 Dec 20 '17 at 16:05
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Put both GFCI and AFCI protection on it, and don't give it another thought.

The GFCI will minimize the risk of electric shock.

The AFCI will minimize the risk of fire.

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