PSNetters & Rich,
I agree that there has been a lot of discussion and a lot of
confusion over Functional Earth.
My ongoing contention is that it is acceptable to carry the earth
into the equipment for functional purposes and bury it there. The next
argument is that this earthing connexion should not have to meet the same
requirements as the PE; ok as long as it is not accessible anywhere on the
product (tinsel wire earth/ground lead). If, however, it is accessible to
any of the required pins & probes then the usual (40A) earthing test is
required and the unit must pass. This is usually a problem where secondary
circuits are attached to earth/ground and this common electrode is
accessible on connectors (such as USB).
You can't have it both ways, tho - declaring the earthing for
functional purposes then making it exposed to user. Not acceptable.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety Engineer
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201 fone/fax
p.perk...@ieee.org
_ _ _ _ _
"This 'functional earth' is indeed a source of total confusion. I don't see
why anything would need one."
One common use is to connect the Y1 capacitors to earth.
"But if it does, the point is that it can be connected by thin wire that
won't carry the PE fault current. It seem silly to me; just use the
necessary thicker wire so that earth/ground is 'protective' and thus the
product is Class I; the cost is minimal and the hassle is reduced to zero."
An easy way to obtain an FE is to connect it to the PE terminal in the
equipment which connects to the PE in the mains cord which connects to the
PE in the building.
My audio equipment is metal-encased two-wire, but it includes a FE terminal
on the back. I suppose this is to facilitate an external antenna. I wanted
to earth the equipment, so I ran a green-yellow wire to the earth (PE) pin
of an otherwise empty plug. A lot easier than running a thin wire to a
separate earth rod.
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