This seemed to me to be a simple question, but it's turned out to be one with
different answers from the experts, so I'm confused. Reading section 5.2.2 of
60950-1, seems to say that an ITE product (computer server specifically) that
is Overvoltage Category II can use table 5B to determine the test voltage,
which is listed at 3,000 Vrms for reinforced insulation for an ac mains of 240
Vrms (340 Vpk). I understand that the working voltage in the power supply can
exceed this value and many of our CB reports definitely show this, but the test
voltage remains at 3,000 Vrms regardless.
Further along in section 5.2.2, it says that for routine tests, the duration of
the electric strength test can be dropped to 1 second and the test voltage of
Table 5C (different table) can be reduced by 10%. But this table seems to imply
that I can reduce the 3,000 V to a test voltage of 2,700 Vrms.
Now table 5B (Part 2), for 340 V, the test voltage is 2,328 Vrms. If I reduce
this voltage by 10%, the test voltage is 2,095 Vrms. If I want to do a DC
hipot, the test voltage would becomes 2,963 Vdc.
I have been given numbers everywhere from 1500 V to 3000 V, and I'd like to
know what the proper test level should be. Is a different test level determined
for every power supply based on working voltage for routine tests? or can one
test level be determined and used for all hipot testing.
As an EMC guy, the range I've been given by the safety folks is only 6 dB
different and quite within the measurement uncertainty :) but something tells
me that the safety folks will have a better number for the test levels and know
the proper way it is derived.
I would like to set the hipot testers to a single value if at all possible. Any
help would be greatly appreciated on what the test level should be for a
routine hipot on a computer.
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