Not only outside, but all 15 and 20 amp 125 and 250 volt receptacle outlets installed in wet locations must have an "in-use" cover. The receptacle must also be listed as weather resistant under the 2008 code. 406.8(B)(1)
I have a few questions what is the difference between damp location and wet location? Then what would a covered front porch be considered. I use a regualar weather proof cover( with 2 flaps) on covered areas and in use covers in areas with no coverage(like 12" overhang)
The general practice, assuming that there are no physical barriers in place, is to go to the nearest overhead projection and imagine a 45 degree line, toward the structure. Above this line is considered "damp;" below it "wet." So, if you assume a porch 10 ft deep, with an overhang 8 ft. above the decking, receptacles on the inside wall would be in a 'damp' location.
The same rule can be applied to receptacles directly under the eaves. And, of course, there would be little sense in using a 'bubble' cover for a receptacle that faced 'down.'
Now .... here's the catch .... there is a general requirement that equipment be suitable for the environment in which it is installed. I would use this as a reason to use a "Bell" box in nearly any outdoor location, however it may be sheltered. Why? Insects. I'm tired of trying to remove covers, only to see six furry legs trying to pull the covers back on! All those little holes in 'normal' boxes make them havens for wasps and spiders.
If the receptacle is in, what is considered a "damp location", a regular weatherproof cover is approved?? This is what I get by reading 406.8 (A) in the 2005 code. So a receptacle that in under a front porch area, if it is not subject to a "beating rain" or "run off", does not require an "in use cover" ??? I have a job that is requiring the receptacles be located on the outside post, under a roofed deck. This is not directly subject to a beating rain,(unless the rain is a blowing rain), but I think I will go ahead and figure in use covers, for the reason that they are using it as an "outside kitchen" and there may be some appliances, such as a small refrigerator, that are left plugged up all the time. Thanks for the comments, Steve...
There are very few instances where you should not use an in-use cover, IMHO. Exceptions, as mentioned above, would be on the underside of an eave (for holiday lighting, etc.) that has virtually no chance of being subjected to direct splash, from rain or any other source (i.e. sprinklers) when a plug is installed.
Why did we suddenly get concerned with a little water splashing on a plug? If it is too much the GFCI will trip. BTW is there an in use cover for the second string of Xmas lights you have plugged in the end of f1rst string? How about the plug on the tool you have plugged into the extension cord? That is a lot closer to the user than the receptacle on the wall. I only have in use covers on the receptacles that will normally have something plugged in them. The ones that are only used for things I will use and put away have snap covers, not wasp condos.
Living in a wet environment, The closed while in use covers are benefical if installed properly. The old gray covers did their job providing they were never opened, hence the stamped message on them, "Not waterproof when used". I have replaced several water damages recepts from open / broken covers that were FUBAR'ed. I have replace ones that were not damaged and rarey used and the device was in mint condition despite being located in a driving rain for 20 plus years. They CWIU covers can be easily damaged though if the recept is an are of high traffic areas. I use them alot up here and several have been busted. I did get a couple of the low profile sample covers that some linked to a while back. It is good concept but I am a little concern with the tension from the flexible portion cover will do to the cord over time and the look of them seem "odd looking" when cocked when something is plugged into them.