In message
<ea4ca5c9ced91040aa61aacf92458866a42...@ukldexm02.global.spiraxsarco.com>
, dated Mon, 8 Sep 2014, "Ian White (SXS UK)"
<ian.wh...@uk.spiraxsarco.com> writes:
Not wishing to throw a spanner in the works - l have to mention
different earths can be at different potentials. Strange but true!
It isn't really strange: it's just that most things are not
superconductors and Ohm's Law applies wherever there is current flow.
But you do raise an important point. The 'internal PE' is effectively a
'remote earth' - it's at the potential of the earth at some distance
from the equipment. This indeed may not be the same as the potential of
the earth at the equipment, and if the PE is effectively also earthed at
the equipment, there is a possibility of a very large current in the
loop so formed, because its impedance is very low. This current could be
induced by local magnetic fields, and there are other possible causes.
I feel sure that the NEC has things to say about this, so local earthing
may not be permissible.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Quid faciamus nisi sit?
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
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