I really don't recommend the extension-cord route, as being risky. Trenching in conduit to run proper service to the coop is not that difficult or expensive, especially if you have an outdoor outlet that you are willing to convert over.
But if you are bound and determined to use an extension cord, for safety's sake
please:
-use a heavy-duty cord
-use as few cords as possible (preferably just 1), meaning, use long
cords
-if you have to use >1 cord, protect where they plug together by
putting it underneath something (a box, a bucket, etc, weighted
or staked so it stays put) and putting the juncture up atop a few
bricks to keep it off wet ground and so that any moisture that gets
on the cord runs downward away from the plugs
-run the cord somewhere it won't catch peoples feet, lawnmowers,
shovels, etc (up along a fence, or inside 1" plastic pipe, or etc)
and
-
plug it into a GFCI-protected circuit (this is a biggie!!). If the circuit
you want to use is not GFCI-protected, anyone with basic electrical
wiring experience, and an inclination to follow directions and test
their work, ahem
, can install it for like $15.
Oh, and make sure you are not plugging in more wattage than the cord is rated to handle (like, if you are running a heat lamp or multiple lamps).
P.S. to original poster: if you're in Wisconsin, you pretty much NEED actual electric service of some sort, not just a solar or battery-powered light, because hauling water multiple times a day and worrying whether it stays liquid long enough for the hens to stay hydrated is NO FUN. You want to be able to use a PLUG-IN waterer or base to keep things thawed, honest
Pat