Dear Boštjan:
Despite UL1741 and UL 840, OVC does not apply to DC. There is
no research that I know of that supports use of AC OVC to DC.
If the 450 V DC is not outside the building or is otherwise not
subject to lightning-caused overvoltages, OVC does not apply.
Likewise, if the 450 V DC only supplies a limited number of other
loads (which are assumed to generate transients when switched
on or off), OVC does not apply.
Since there is no isolation from input to output, whatever insulation
between input and output is "functional" insulation. The transients
that appear on the AC output side (generated by load switching and
lightning) will also appear on the DC side.
120\240 V overvoltages are OVC II and are 3 kV according to
IEC 60664, not 4 kV.
Best regards,
Rich
On 8/6/2014 10:39 AM, Boštjan Glavič wrote:
Dear experts,
I am trying to figure out how to determine correct spacings for
non-isolated inverter. According UL1741 OVC IV needs to be considered
for inverter. From table 8.1 from UL840 I get a transients of 8,0kV
for 450VDC input. Is that correct?
Output of inverter is connected to AC grid 120/240V. This results in
4kV transients.
We have no insulation input/output. Which transient level should I
then use? 8kV transient on AC output side is almost impossible for the
design.
Any idea?
Best regards,
Bostjan Glavic
SIQ
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