On Fri, 16 May 2008 07:32:12 -0500, "BretLudwig" <bratzirules@[EMAIL PROTECTED]
>
wrote:
> The US common 110-125 VAC plug started out as a two blade symmetrical
plug
>and socket. At that time, it did not matter which was neutral ("earthy"
in
>UK parlance) and which was hot. The polarized two wire plug, which
>accepted nonpolarized plugs in its jack but not the other way around,
came
>out I believe in the 1930s.
It may have "come out" in the 30's, but an awful lot of equipment from
the sixties still had non-polarized cords on them. Non-polarized
receptacles have been banned from use in new construction since 1962.
FWIW, the 3-wire grounding plug & receptacle was patented in 1928.
>It served two purposes: it kept hot chassis
>equipment with its chassis at neutral rather than hot, at least
>theoretically and it kept reverse polarity off DC appliances in those
>situations where DC was provided for domestic use, in large apartment
>buildings in major cities and in offices and even a few homes immediately
>adjacent to DC rail services. There were apartments in New York City
>supplied with DC only until quite modern times although it was
>aggressively phased out once color TVs became de rigeur.
>
> The third ground ("earthed", as distinct from "earthy" in UK
>terminology)prong came in a little later.
From the '08 NEC:
Ground = Earth (it took a whole committee to figure that out ;o)
The neutral is called the 'grounded' conductor, and the bare or green
is called the 'grounding' conductor (have been for a long time).
> In ANY polarized two pin or ANY three pin socket (I have never seen a 3
>pin not polarized) it is a violation of code always and everywhere to
have
>any of the three hooked up wrong. Every US home (unless Amish or
otherwise
>without electricity) should have a standard common plug tester, available
>everywhere, cheaply ($2-10) that plugs in and lets you know if the outlet
>is wrong.
>
> Of course, most homes built after WWII in the US have both "110" (which
>has crept up to at least 117 and sometimes almost 130 volts most
>everywhere) and "220" (double that) sockets and service. The 220 is
>limited to the hardwired HVAC and to plugs for the range and dryer, and
in
>older homes or those with rooms off the air circulation pattern,
>underwindow air conditioner outlets.
Electric baseboard heat, also.
>It's interesting that there are at
>least five different, incompatible 220 outlets in semi-common use.
There's a reason for that. You don't want to be able to plug a 15-amp
air conditioner into a 30-amp receptacle.
>Some
>are three (hot-hot-ground) and some are four (hot-hot-neutral-ground)
>conductor, as some appliances use both internally. The three pin 220 ones
>use only 220 internally, the ground not being allowed as a return.
Which is why in all new construction, all 240V residential range &
dryer outlets must be 4-wire. Nema 14-30 (dryers) and 14-50 (ranges).
The problem was that many of those units *were/are* using the
grounding conductor as a neutral.
>http://www.arthistoryclub.com/art_history/Split_phase
>
>http://www.stayonline.com/reference-nema-straight-blade.aspx
>
>http://en.wikipedia.org/wiki/NEMA_connector
>http://en.wikipedia.org/wiki/Domestic_AC_power_plugs_and_sockets
>
> There are also 277 three pin outlets (window units in motels and such)
>and various three phase connectors. Unlike in Europe, it is virtually
>impossible to get three phase service into a residential swelling in most
>areas in the US: utilities are convinced you are running a sweatshop or
>growing dope hydroponically in the basement if you want it fitted.
There isn't a whole lot of residential equipment that runs on 480/277.
It would be expen$ive, and you'd still need a big xfmr or a separate
service for the 120/240. What's the point? Smaller conductors would be
the only advantage. A watt is a watt, so you wouldn't save money on
your electric bill.
(you can get 240v grow-lights and a Roto-phase to make the 3rd phase
for the sweatshop equipment)
DC
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