At 10:26 AM 2/12/98 -0800, you wrote:
>On 11 Feb 98 at 20:37, Stephen J. Link wrote:
>
>> The way to wire the switches should be on top of the power supply.  If
it is
>> connected improperly the worst it will probably do is trip the circuit
>> breaker.
>
>  Since this is AC[*], polarity doesn't enter into it.  There are
>only two basic possibilities:

The power line carries lethal potentials! Much thought went into the
present standard for connections to the power lines. AC does NOT mean that
polarity doesn't matter. There are three connections to modern AC power
plugs. The round pin on the plug is intended to be connected to the metal
case. It is connected to "Earth ground" through the wall outlet. The wide
flat blade is connected to the "neutral" power connection which is the
closest potential to earth ground. Power supply designers connect this to
the wiring most likely to have a fault connection to the metal case. The
narrow flat blade is connected to the "hot" power connection which has the
AC potential (120VAC) measured with reference to the "neutral" connection.
In the United States, the convention is to use "natural" (white) color
insulation for the neutral connection and any othe color for the "hot"
connections (red, black etc.). The wiring for light switches has other
conventions not covered here.
It is very important to follow the manufacturers recommendations in
connecting the power line to the power switch which controls the power
supply. If you do not have some sort of continuity checker, get one! A
small battery operated (two AA cells and a light bulb) checker is only a
few dollars at places like Radio Shack.
The round pin of the power cord should have continuity to the metal case
and is usually connected internally in the power supply. The power switch
usually has four connections. These consist of two pairs which are
connected when the switch is on and disconnected when the switch is off.
With the continuity checker check the switch connections without any of the
wires connected. I'll refer to the connections to the switch as A, B, C,
and D. With the switch turned on, A will be connected to B but not C or D.
In a similar manner, C will be connected to D but not A or B. Connect the
power wires with continuity to the wide and narrow flat blades to A and C
respectively. The C terminal should be the one that is the least likely to
be touched accidentally and is connected to the wire with continuity to the
narrow flat blade. The A terminal is parallel to the C terminal and is
connected to the wire with continuity to the wide flat blade. With the
international color codes, the wires from the power cord will be black and
white wires connected to the A and C terminals of the switch. The wires
connected to the power supply are usually brown and blue which are
connected to terminals B and D. In this way when the switch is turned on,
the black is connected to brown and the white is connected to blue. In at
least one power supply I have (typical of new power supplies), the power
cord is connected internally and a four wire cable to the switch has
connections like this:
Wide ----- Black ---->C Switch D<----Brown
Narrow--- White----->A Switch B<----Blue

Proper connections to the power line and power switch can prevent lethal
shocks!
Do it right.

David Figueroa
--
Internet Communications of America, Inc.


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