Re: Potentially stupid question about AC

[dalloff@gcfn.org (Dave Althoff)]

David Wilson (david@uow.edu.au) wrote:
: supertimer@aol.com (Supertimer) writes:
: >Rubywand <rubywand@swbell.net> wrote:
: >>Supertimer writes ...
: >>
: >>S______(hot)_______________ typically Black (220V from hot to hot)*
: >>S
: >>S                110V
: >>S____(neutral)__________    typically White*
: >>S
: >>S                110V
: >>S______(hot)_______________ typically Red*
: >>
: >>
: >>(110V and 220V are the traditional values. The actual voltages are going to be
: >>closer to 115V and 230V.)

: I have seen US gear marked for 110, 115, 117 and 120VAC. Japan uses 100VAC.

: Here in Australia we have 3 phase power instead of the two phase shown above.
: Most recently wired homes just have one of the 3 active wires and the neutral
: coming into the switchboard. Our actives are 240VAC and between any two actives
: we have 415VAC. Our color scheme for building wire is Red = Active, Black
: = Neutral and Green or Green/Yellow striped for Ground. This can cause problems
: with US/Canadian gear - we had an entire lab of Volker Craig terminals wired
: with Black = Neutral, White = Active and Green = Ground (I do not think the
: importer knew Black is active in USA).

Here (USA) 3-phase is generally reserved for industrial equipment,
particularly large motors (refrigeration equipment is a frequent 3-phase
item), also 3-phase is generally used in commercial buildings with lots of
circuits.  Household wiring is generally just single phase 230v.  In 3
phase you get into that strange 208v stuff... 8-)

: If all three active phases are present they are Red, Yellow and Blue.

: Appliance wiring tends to use the European standard of Brown = Active, Blue
: = Neutral and Green/Yellow stripes for Ground.

: Here we use the MEN system - Multiple Earthed Neutral.

: 		Fuse Box
: 		------------				+-------+ Metal case
: Active ---------|----------|------- Active -------------|--/ -) | is earthed
: 		|          |				|     ( |
: Neutral---------|--+-------|------- Neutral-------------|-----) |
: 	     	|  |       |				|	|
: 	     	|  +-------|------- Ground -------------+-------+
: 	    	---|--------
: 	    	   |
: 	copper stake
: 	into earth

: Because normal current flow is via the active and neutral leads and they have
: some resistance the voltage at the far end of the neutral lead is typically
: non zero.

: Many houses now have ELCB (Earth Leakage Circuit Breakers) which trip if the
: current in the active line is not equal and opposite to that in the neutral
: line. This indicates that power is getting to ground either via the ground wire
: or through something or someone else.

GFCI (Ground Fault Circuit Interrupter) here.

: Double insulated gear omits the ground wire and replaces the metal case
: with two independent insulating layers.

: Our plugs are Crowfoot so polarisation should always be maintained.

: active	/	\  neutral


: 	    |  earth
: >And why is it dangerous to defeat a polarized plug?

: The device may only have a single pole power switch which breaks the active
: line. The fuse should also be in the active lead.
: --
: David Wilson  School of IT & CS, Uni of Wollongong, Australia

--Dave Althoff, ][.
-- 
    /^\        _       _                *** Now open EVERY DAY!!! ***
   /XXX\      /X\     /X\_      _     /X\__      _     _        _____  
  /XXXXX\    /XXX\  _/XXXX\_   /X\   /XXXXX\    /X\   /X\      /XXXXX
_/XXXXXXX\__/XXXXX\/XXXXXXXX\_/XXX\_/XXXXXXX\__/XXX\_/XXX\_/\_/XXXXXX