On Sat, 5 Jan 2008 21:34:00 +0200, Geoffrey S. Mendelson wrote:
>Not here, the hot lead is 230 volts, the neutral is neutral and ground is
>a saftey ground.
That's because YOUR power system, like those in EU, is an unbalanced 230V
system -- or 230-0-230 for larger loads. The North American power system is
120-0-120. Ordinary loads are unbalanced, from one of the 120V lines to
neutral.
As others have noted, it is NEVER acceptable for a green wire (safety
ground) to carry load current. That is true in EU, it is true in North
America, and it is true elsewhere.
The green wire is a SAFETY ground -- it is present so that it can blow a
fuse or breaker in the event of an equipment fault that causes the chassis
of equipment to be "hot" and kill someone who touched it.
It is NEVER safe to connect neutral and ground at equipment, or to connect a
load between "hot" and the safety ground, and it also causes serious noise
problems. The reason is that when equipment is wired properly, all the load
current flows "out" on the "hot" conductor and returns on the neutral (or,
in the case of a 240V load in North America, out on one "hot" and back on
the other "hot." In those conditions, the FIELD associated with the load
current is confined to a small area between and immediately surrounding
those wires. If the neutral were to be grounded at the load end, return
current spreads out between all of the ground paths between the source and
the load, and the FIELD associated with that current is large and spread out
over that area. This kind of wiring fault is a VERY serious one, and a MAJOR
cause of noise, both at baseband (power and its harmonics) and RF (power
supply hash, switching transients, etc.).
For additional discussion of this see the Power and Grounding tutorial on my
website.
http://audiosystemsgroup.com/publish
73,
Jim Brown K9YC
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