In a message dated 97-04-30,Barry Schwartz wrote:
<< The switch can be either before, or
after the relay (or light or whatever). >>
This is true, as is everything else he said; However, there are good reasons
for placing the switch in either the positive or negative side of the telay
or other device. Rather than thinking in terms of positive or negative, think
in terms of "hot" or "ground." For example, if a switch is loacated in a
harsh environment, such as under the car, it is best to switch the ground
lead. That way, if mud, rocks, etc, damage the wire, the only thing that can
happen is the device is turned on. If the hot side were switched, a short
could cause meltdown. On the other hand, brake and reverse lights are
switched in the hot lead. If the ground lead were switched, a hot lead would
need to be ran to the lights. The trunk is a hazardous location, with cargo
sliding around. By switching the hot lead, power is available around the
trunk area only momentarily, while the brakes are on, or the transmission is
in reverse, minimizing the meltdown possibility.
I know this is more than anybody wanted to know, but I've started talking,
and I can't shut up!
Dan Masters,
Alcoa, TN
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