Hi Rick:
> The obvious question I would have is... why couldn't you test at a higher
> current for longer time meeting both requirements? For example 30A for two
> minutes. I know the document indicates a maximum current, but does this make
> sense?
The original question appeared to me to ask why there
are two different test currents.
Of course, if you test at 30 amps for 2 minutes and pass,
then you have also passed 25 amps for 1 minute. But,
keep in mind that some certification houses MAY not agree
with this premise.
EN 50116 specifies a maximum current so that the test
itself does not damage the circuit. If 25 amps is okay,
and 30 amps is better, then why not 50 or 100 amps? If
the current is high enough, then the circuit will indeed
be damaged by the test.
The requirement is that the grounding circuit, which
handles the fault current return to the source, must be
equally robust as the supply circuit which provides the
current from the source (breaker) to the load. In practice,
the supply circuit and the grounding circuit, both designed
for 15 amps continuous, will easily handle twice that for a
short period without overheating -- the wire may get warm,
but it won't overheat!
Hmm. Why don't we test the supply (primary) circuit for
30-amp fault current? It would be seem as bad for the
supply circuit insulation to fail as it would for the
grounding circuit to open! Well... answering my own
question, the supply circuit would fail to the grounded
metal, and the grounding circuit provides the protection.
Best regards,
Rich
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