Hi Mike:
> I'm posting this for a friend who is having a problem with CSA and hipot
> testing. He has several products which operate on 115/230 VAC. They are
> industrial control products (don't know the CSA standard number but they
> fall under UL508 is the US). In one CSA report he is required to run a 1500
> VAC hipot for one minute (1800 VAC for one second), in another CSA report he
> is required to run 1000 VAC for one minute (1200 VAC for one second).
>
> I know the CSA hipot requirement is elusive and is required by the Canadian
> Electric companies. Can anyone help me give this guy some guidance? My
> feeling is that the 1500 VAC requirement is the "type" test and he should be
> using the 1000 VAC value for routine production tests.
>
> He has been told by CSA that anything under 50 VAC gets tested at 1000 VAC
> and that anything over that gets tested at
> 2 x rated voltage +1000 for production line tests. Seems strange.
Hi-pot test voltages are not standardized, although
IEC SC28A has attempted to do so in IEC Publication
664.
Standards such as UL 508 are not subject to
international standardization, so there is little or
no influence of IEC 664 on the test requirements in
UL 508 and the CSA equivalent.
So, to understand the CSA requirements, we must look
at the history of hi-pot test voltages.
In North America, in the 1960s and 1970s, virtually
all products were 120 V. We simply were not in the
international marketplace. (Those that were, their
products had to be internally re-wired -- by the
customer -- with a soldering iron -- to operate at
220 V or 240 V.) There were no switch-selectable or
wide-range products.
At the time, the "standard" hi-pot test voltage in
both the USA and Canada was either 900 or 1000 V rms,
depending on the standard. For any other voltage,
the standard was 2V + 1000, where V is the rated
voltage. Thus, for a product rated 220 V, the test
voltage was 1440 V rms. Later, the formula,
2V + 1000, was applied to all voltages, so for
products rated 120 V, the test voltage became 1240 V
rms. These were often rounded to 1250 V and 1500 V.
So, now we have four test voltages, 900, 1000, 1250,
and 1500. And, nobody understood why we needed to
do such testing. Often, we felt that this testing
represented some kind of abnormal condition, but,at
the same time, it seemed quite unreasonable to expect
the mains to go such a high voltage. But, we went
ahead and did the testing, usually without any
difficulty.
Because of the lack of understanding of the purpose
of the hi-pot test, back in those days hi-pot testing
was applied to any terminal that was connected to an
external voltage source. So, even low-voltage
circuits were subjected to the minimum hi-pot voltage,
1000 V.
So, in answer to your colleague's question, all of
the CSA-required hi-pot voltages are correct. They
simply are not standardized, either within the
standard or among standards. I believe the same
situation exists in UL.
If your colleague wants standardization, he can
simply choose to test his products at the worst-case
CSA-required voltage.
However, his particular CSA engineer may not allow
this. The problem is that the standard specifies
the hi-pot voltage. Any test voltage that is not
that specified in the standard means that the test
is not conducted per the standard and is therefore
not acceptable (even though the actual test is a
worst-case test). Many certification engineers are
unwilling to accept data that is not in accordance
with the standard. Indeed, there is a good reason
for a certification house to not accept a worst-
case test voltage. That voltage may be damaging
the insulation; the test house does not want to be
seen as requiring a test that could be damaging the
insulation and thereby causing a safety problem.
So, the certification engineer may require testing
at the voltage specified in the standard. He will
say that if you want to test at worst-case, that is
your perogative, but that is over and above and in
addition to the certification house test.
Best regards,
Rich
ps: Perhaps Egon will offer his explanations and
put a different spin on this question.
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