On Wed, 16 Nov 2005 04:05:51 -0800, R.Measures wrote:
>My 240V, 40A circuit is wired 2-hot and 1-neutral. I assumed that no
>"safety" ground wire was needed because neutral is connected to
safety
>ground in the circuit breaker box. Under normal operation, virtually
>zero current flows in the neutral wire.
NO, NO, NO, NO, NO!
Neutral is intended to carry current (although it is not used in the
240 volt circuits in homes). Ground is a PROTECTIVE conductor that
should NOT carry current except in the case of a fault. (A fault is a
failure of some component or wiring that results in an equipment
enclosure being hot).
The function of the safety ground is to provide a path for fault
current that blows the breaker and protects the user from shock (and
fire). Electrical codes require that the safety ground (from the
breaker panel) be connected to the equipment enclosure (via the green
wire).
>In my opinion, the folks who got paid for updating the NEC
>probably realized that if they didn't make at least some changes,
>eyebrows would be raised by bureaucratic bean counters. Another
>factor may have been that they knew little about circuit analysis and
>Ohm;s Law.
You are quite mistaken. First, people who write most codes and
standards are often doing so on a voluntary basis. As vice-chair of
the EMC Working Group of the Standards Committee of the Audio
Engineering Society and a member of a half dozen other working groups,
I can tell you that the people who write standards are usually the
brightest and best. I know a few of the people who contributed to the
part of NEC that addresses grounding and bonding, and they are VERY
good EE's.
I suggest you study the Power and Grounding "White Paper" on my
website, which is a free download. Mike Holt (www.mikeholt.com)
teaches good electrical practices and the NEC to electricians, and has
written excellent materials to go with his classes. He sent me his
excellent document on "Grounding and Bonding." It is not free. :)
Two other excellent references are the IEEE "Green Book" and "Emerald
Book," both of which are IEEE Standards. They are published and sold
by the IEEE.
Jim Brown K9YC
http://audiosystemsgroup.com
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