Joel, et al,
Many great comments have been made in this discussion so far; thanx to the
PSNet folks experience being shared here.
From an operational point of view equipment either depends upon earthing
(the second level of protection after the basic insulation) or double
insulation for protection from electric shock. We have come to learn from our
lengthy discussions in developing the new Hazard Based standard that there are
conditions which are outside the control of the equipment manufacturer and,
when they occur, are abnormal situations. The availability of earth is one of
these; it may not be properly connected in some situations or it may not be
provided (such as in Japan or Netherlands or Norway) because of the local
electrical system codes and practice. In either case our standards limit the
current in the earthing conductor to prevent hazardous electric shock. The
connection within the equipment must be robust and not accidentally defeated
during maintenance or repair. The use of a single earthing connection for the
principle ground is appropriate here. The use of lockwahsers and double nuts
is another good practice for additional connections where they cannot be
independently done.
Further, standards keep moving to a performance based set of requirements
rather than a construction based set. This makes it difficult to pass good
practice along in our business. So we need to listen to the experienced
practitioners and carry these good practices along. This is not as satisfying
as being able to point out the specific wording in your standard, but it makes
good sense solutions for many cases.
:>) br, Pete
Peter E Perkins,
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201 fone/fax
p.perk...@ieee.org
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