<div dir="ltr"><div dir="ltr">I'm no expert although I was told the import aspect of insulation testing is the duration of the reading - a reading should be at least 1minute, up to 10 minutes for large equipment... and the resistance should always increase. The Megger manual (<a href="https://www.instrumart.com/assets/Megger-Guide-to-Insulation-Testing.pdf">https://www.instrumart.com/assets/Megger-Guide-to-Insulation-Testing.pdf</a> page 15) suggests sampling at the 60 second and 30 second marks and using the ratio.</div><div dir="ltr">/s<br><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, 25 Jan 2021 at 11:33, Mark Beckett <<a href="mailto:m.beckett@amuri.net">m.beckett@amuri.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div bgcolor="#FFFFFF">
<p><font face="Candara">A word of caution about testing cables well
beyond their rating.</font></p>
<p><font face="Candara">It punches holes which later become a
problem.</font></p>
<p><font face="Candara">We have a number of communication cables
that are 120v rated, and were tested using 500v meggers. We're
now seeing many fail.</font></p>
<p><font face="Candara"><br>
</font></p>
<p><font face="Candara">Mains cables and devices are tested at twice
their rated design (ie 500vDC) UNLESS it has a specification to
only test at 250VDC.</font></p>
<p><i><font face="Candara">We have a number of power supplies that
have protection devices rated at 250v.</font></i></p>
<p><font face="Candara"><br>
</font></p>
<p><font face="Candara">Tenma make a low cost fully rated device
that sometimes appears on special.</font></p>
<p><font face="Candara"><a href="https://nz.element14.com/tenma/72-9400a/insulation-tester-1kv-5gohm/dp/249951801" target="_blank">https://nz.element14.com/tenma/72-9400a/insulation-tester-1kv-5gohm/dp/249951801</a></font></p>
<p><font face="Candara"><br>
</font></p>
<p><font face="Candara">Mark<br>
</font></p>
<br>
<div>On 25/01/21 00:49, Andy Gardner wrote:<br>
</div>
<blockquote type="cite">
<br>
On 24/01/21 10:41 pm, Mark Atherton wrote:
<br>
<br>
<blockquote type="cite">The modern insulation used on enamelled
copper wire (even the thin stuff) seem to tolerate 5kV OK. I
have also tried the lowest voltage cable I could find (CAT5) and
strapped a twisted pair across the unit at full smoke without
incident.
<br>
</blockquote>
<br>
Cat 5 has polyethylene insulation rather than the more common PVC.
<br>
<br>
<br>
<br>
<br>
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