in the mood to type-
we do inline female and even sometimes inline male plugs. inline female slider plugs ("vampire") are great for adding a wreath or wreaths along the c-9 cord run. as long as you don't exceeed the amp rating or whatever c-9 cord you run, I am fine with that. an inline male is great for stakelights near outlets and for top c-9 soffit outlets to run power both ways. but I always tend to prefer 2 male sliders and use an extension cord with a 3 way and give me a way to run power a third direction if need be. You do have to be sure and have the 3 way out of gutters and the flow of water in valleys on roofs to help avoid GFCI tripping.
on polarity-The UL listing or rating on plugs is what pushes the polarity. a polarized 2 prong plug is rated for greater than 3 amps. anything 3 amps and under has two little non poloraized tabs. grounded plugs have the third round tab, but are not necessarily indoor or "outdoor". my computer charger has a grounded plug and it ain't outdoor rated.
UL labs is trying to protect you from plugging in a cord rated a higher amperage into a cord that is rated a lower amperage. for example, plugging in a c-9 strand with 140 bulbs into the back of a light link. even though you can grind down the polarized plug and can make it go in there, that female receptacle, the wire, and the fuse in the front end is not manufactured for and not rated for the heat that that many amps generates.
I know that everyone seems to love making their own jumpers or cords, but I encourage folks to add up the cost of the wire per foot shipped to you, and the cost of the 2 ends of the cord and then compare it to the cost of 16 guage 6, 9, 15ft lamp cords you can buy in white, brown, or green locally at Walmart, home depot or Lowes. we have made cords before, and we still do some, but I have found guys work faster and it costs less to buy premade cords with 3 ways on them.
I also found that making cords brings problems to the table. I have caught employees constantly pushing power the wrong direction by creating male/male cords which creates a dangling hot male plug somewhere that can cause a shock and or fire. I have found that slider cords have a failure and short rate about 10 times that of manufactured cords. and while 16 guage lamp cords can handle 12-15 amps on short runs, 18 guage spt-1 and spt-2 will melt.
slider cords make sense to me when you need to jump 19 feet from a c-9 cord run to a wreath or star at a peak and then you are done. maybe you need to hang a starburst above an entry and you want a white cord to go up 35 feet up there. but if something is 6, 9, or 15 foot away it is almost always cheaper and quicker to use a premade 16 guage cord, and have the convienience of the 3 way to plug in another cord to go somewhere else.
I have had conversations with electricians, GFCI's popping, about "indoor" or "outdoor" cords, it seems to boil down to the grounding round tab and the air cavity in many 3 ways on those less expensive cords. The 3 ways on indoor cords do seem to attract water and can cause GFCI tripping unless you locate them properly. I am at a loss to understand while c-9 cord, and every other christmas light item used out doors with any type of bulb I have seen is not grounded, yet every cord rated as outdoor and every timer rated outdoor is grounded. indoor 16 guage spt-2 lamp cords without grounds are rated on the package for 15 amps. I have always had fun arguing with electricians who say you always have to use outdoor rated cords outdoor because they are grounded, yet no wreath, garland, mini-lights, display or anything you can buy Christmas wise is grounded. I know that grounding "protection" should extend from the socket as far as you can go, but I am not aware of any instance any client of mine ever got shocked by any of my jobs any time. although my employees seem to find the time at least on a weekly basis to shock themselves on c-9 cord while installing.
