When I started my current job in June of last year, I was surprised to find out that a lot of our "two-fers" were actually edison outlet taps (the entire space is edison). I reluctantly accepted this fact for the present but resolved to solve it in the future. Over the course of the season, I used some of my dead time in between productions to fashion "real" V-style twofers from surplus plugs and cable. I'm now proud to say that the taps are entirely gone.
But I got to thinking, as I was spending all this time making two-fers, that I couldn't entirely blame my predecessors for thinking outlet taps were a good choice; after all...
1. They are UL-listed (I believe) and rated at 15 amps, which isn't a FULL dimmer load, but enough for three source fours or similar instruments, which is about the limit I'd put on a dimmer anyway. Besides, it's not wrong to use, say, 14-gauge cable with a 20 amp dimmer, because in a professional environment it's assumed you know what you're doing and won't overload it.
2. They are cheap, costing only about as much as a single edison plug (on a two-fer there are three plugs, two of which are the typically more expensive female, plus a few feet of cable, which also costs).
3. You don't have to spend any time to make them, and finally...
4. They are professionally manufactured and have no flexible parts. Why is it that we would consider a two-fer made by hand perfectly safe and preferable, and not a solid block of plastic with no wires to come loose? I can think of so many failure points of a self-made two-fer; after all, they aren't even made in such a way that uses the male plug in a manufacturer-intended way.
I've seen two-fers made in horrible ways, with no strain relief because someone tried to use 12-gauge SO and it wouldn't fit, so they just took off a few inches of rubber and replaced it with e-tape, then clamped the strain relief down on the inner conductors. What would you reccommend then, these jury-rigged devices or an outlet tap?
Trust me, I'm firmly of the belief that what goes in your grid should not be the same thing used to power your toaster oven, but I'm looking for solid justification for this belief. Thoughts?