From: haggisz@hotmail.com   
      
   bud-- wrote:   
   > On 10/6/2017 12:17 AM, gfretwell@aol.com wrote:   
   >> On Fri, 6 Oct 2017 02:12:15 -0400, "Anon Y. Mouse"   
   >>  wrote:   
   >>   
   >>> I have an old (1940s I think) ceramic outlet in a box, for a two prong   
   >>> plug, no ground. It accepts a standard US 2 prong (1-15) plug. It is   
   >>> polarized. It is also marked "15A 125V" (molded in the ceramic).   
   >>>   
   >>> The box also has 2 standard fuse holders, one in series with each slot.   
   >>>   
   >>> However, both slots are T-shaped, like one slot is in a 5-20 or 6-20   
   >>> outlets. Almost as if it was designed to accept a 2-15 plug (does such a   
   >>> thing exist?) as well as a standard 1-15 plug.   
   >>>   
   >>> Why are the slots T-shaped?  Were 2-15 plugs a thing for 220V at the   
   >>> time, they installed the same outlets on both 110V and 220V circuits,   
   >>> and you just had to know which outlet to plug in the 110V things and   
   >>> which to plug the 220V things in? And if you got it wrong, too bad?   
   >>>   
   >>> That's what I thought when I saw these in older houses. But this one is   
   >>> explicitly marked for 125V max, so it's not intended for 220V.   
   >>>   
   >>> For a 110V circuit, one fuse would be in series with the neutral, not a   
   >>> good idea. But it would make sense if used on a 220V split phase   
   >>> circuit.   
   >>>   
   >>> Why are the slots T-shaped?   
   >>   
   >> There were receptacles many years ago that would accept a 1-15 or a   
   >> 2-15. I would like to think they have been replaced by now because it   
   >> requires a whole lot of care by the user that they know what they can   
   >> plug in.   
   >>   
   >   
   > As everyone probably figured out, this is US.   
   >   
   > Used to call them T-slots, and they were used to replace 120V   
   > receptacles where there was no ground. I have several in my collection,   
   > by Leviton,  P&S,  Homart. There is a picture at the   
   > font-of-all-knowledge, second pic down, right end.   
   > https://en.wikipedia.org/wiki/NEMA_connector   
   >   
   > One of mine (and only one) is labeled 15A 120, 10A 250V, and is UL   
   > labeled. Marked with patent number "1591773-1591707". I assume that   
   > isn't useful, I am too lazy to look.   
   >   
   > I have never seen a 2-15 plug for 240V. But long ago I found a plug like   
   > a 2-15 intended for 120V, so I believe T-slots were for compatibility   
   > with ancient plugs. Likely weren't 240V receptacles back then.   
   >   
   > I forgot the parallel slots were polarized, all of mine are. The Ts   
   > aren't polarized.   
   >   
   >   
   > I once had an ancient vacuum cleaner with a plug like an Edison lamp   
   > base. It would turn freely with respect to the cord until it was tight.   
   > I assume in the real early days you could remove a light bulb and screw   
   > in the plug.   
   >   
   > Probably matching the above, somewhere in my collection is a   
   > 'receptacle' that matches the Edison lamp base plug. Mounts the same as   
   > modern receptacles. Nice brass plate with a brass door that opens.   
   >   
   >   
   > Would think "standard" fuses would make the device rather large.   
   >   
   > First place I lived away from home was a duplex with a 30A 120V service.   
   > The service and 2 branches had neutral (plug) fuses. There used to be a   
   > solid brass shell with ceramic center with a slot for a screwdriver that   
   > could be used to eliminate neutral fuses.   
   >   
   >   
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