Imagine that you bought a few strings of incandescent Xmas lights. They are rated for indoor use only. The tag says not to use them outdoors. They aren't any cheaper than the outdoor-rated lights sold in the same store; but you feel that the indoor-rated lights come in nicer colors.

You want to use them outdoors for about one every per year (in the fall). They'll be used in a backyard hut. They'll be attached to the roof of the hut, which is made of bamboo poles. The roof is not watertight at all. The lights will remain lit all night, every night. They'll be plugged into a GFCI-protected outlet.

After the week is over, the lights will be stored away in a dry basement until the next year.

It can get chilly here in the fall -- it can dip to 5 °C (40 °F) at night. It also rains sometimes.

Rain will fall on the lights, and they'll get wet.

  1. What are the risks?

  2. (Optional:) If you like, also consider your favorite North American electrical code. Either the US National Electrical Code or the Canadian Electrical Code. Is it likely to be legal to take risks like this one?


If the instructions on the labeling specifically say "For indoor use only". Then installing them outdoors is a violation of NEC 110.3(B).

Risks include, but are not limited to...

  • Electrocution
  • Damage to property
  • Injury and/or death
  • Malfunction
  • Reduced product life
  • Voided warranty

National Electrical Code 2014

Chapter 1 General

Article 110 Requirements for Electrical Installations

110.3 Examination, Identification, Installation, and Use of Equipment.

(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.


The main risk I can think of is electrocution. Most likely the parts are not designed to get wet, exposed to sun, and/or extreme temperatures. GFCI will protect you if you get electrocuted and the voltage goes to the ground, but if you happen to get electrocuted in a way that continues through the wiring back to the neutral, there will be no voltage difference to cause a trip.

The electrical codes cover the wiring in the wall and to the outlets. But from the device plugged into the receptacle on, it gets into consumer safety and groups like UL. The product you selected was deemed unsafe for this purpose by the manufacturer or an underwriter, so it would be best to get a product designed for the purpose you intend. As an aside, outdoor rated holiday lights are common and cheap, so it doesn't make sense to try to save money like this.


This is generally a bad idea. If they were safe to use outside, the company would have labeled them so.

If you insist on trying the experiment, make very sure that they're connected to a GFCI so that you don't shock anyone. I'd argue for an AFCI as well to reduce the chance of starting a fire — by which point you've pushed the cost above just getting outdoor-certified lights.

Also: If the bulbs aren't designed for use in the rain, water can cause the hot glass to shatter.

  • I agree generally, but my only concern with this answer is the assertion that using a GFCI and AFCI will have pushed the cost above the cost of an outdoor-labeled string of lights. I don't know if that's actually the case. Technically, it's a requirement that your outdoor receptacles be GFCI's anyway, and I feel like AFCI is massive overkill for something like this. The only ways you're like to get a spark are if a bulb shatters or there's a short in the string, and in either of those cases the GFI will trip. – Craig Oct 7 '15 at 22:59
  • In the US, there are many, many houses still running lights outside without a gfci.. Adding one is cheap, but so is a more appropriate string of lights. – keshlam Oct 8 '15 at 1:06
  • I'm just saying that running anything electrical outside technically requires a GFI in order to be legal. Of course, somebody might run an extension cord out a window or something. Still, $12 for a GFI/GFCI receptacle is cheap insurance and absolutely 100% regardless of whether the light string is labeled for outdoor use, it needs to be running through a GFI. – Craig Oct 8 '15 at 1:30
  • Craig: Not arguing, just realistic about how often this rule is honored in the breech. Let me think about editing. – keshlam Oct 8 '15 at 1:32


How can I tell the difference between interior or exterior Christmas lights? My intentions are to put it on a tree outside. Frankly wouldn't care if it burnt down! will save me from cutting it next summer ;)


The notion of using indoor lights on an outdoor tree doesn't rank very high in the annals of common sense. You may wind up having a fire call (some FD's bill you for these things) or a tripped breaker, melted extension cords stuck to the stoop, etc. But, of course, if you relish the excitement of having the Red Cross people bringing coffee and things to the firemen as you stand around and chat with neighbors among the embers, go ahead. It will be a memorable holiday, and your insurance rates may only spike for a couple of years. Merry Christmas.


FYI: (christmas-treasures.com)

A Christmas light set that is UL listed for indoor use will have a green holographic UL sticker on the cord. A Christmas light set that is UL listed for indoor/outdoor use will have a red holographic UL sticker on the cord.

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