The flash test is necessary because there are high-voltage pulses on the
electricity supply caused by switching operations and distant lightning.
It is very likely that a product that fails the insulation resistance
test would fail the high-voltage test as well. But it is not
inevitable; a 1.8 megohm insulation resistance passes 1.67 mA at 3 kV.
As I said, it would be most unusual for a non-faulty modern product to
show an insulation resistance as low as 1.8 megohms (if discharge
resistors are disconnected).
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On 2018-02-19 09:30, Scott Xe wrote:
John,
I almost forgot the Megger gear that I tried it once in the lab when I
studied radio engineering. Thereafter I am using battery-operated
tester and now more and more multi-purpose testers including it into
one unit.
The main reason why I raised this query is that the flash test gives
harsher test on safety strength than insulation resistance test. The
debate is in safety standards it still requires it but a lot of young
engineers consider waste time if flash test is included. Why do we
focus on flash test? Probably, it is a very old test and still remain
in many safety standards.
Regards,
Scott
*From: *John Woodgate <[email protected]>
*Date: *Monday, 19 February 2018 at 4:22 PM
*To: *Scott Xe <[email protected]>, <[email protected]>
*Subject: *Re: [PSES] Insulation resistance test
The test is very old, and pre-dates the high-voltage test by very many
years. You mentioned 'Megger' in your other post, yes, that was how it
was done. (A Megger (brand name) was/is a type of magneto with an
ohmmeter attached. The stable output voltage required for the ohmmeter
is achieved by a mechanical governor, which limits the armature speed
however fast you turn the handle.)
The test might not be totally irrelevant for modern electronic
equipment, but the requirements in most standards are certainly in
need of revision. These requirements are for a minimum insulation
resistance of 1 or 2 megohms. A modern piece of electronic equipment
typically has a resistance of hundreds of megohms (unless condensation
occurs), so a measured value of a few megohms shows that something
is in fact seriously wrong. I have raised this point in TC108 before,
but no-one was willing to take action. Tradition, you know.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associateswww.woodjohn.uk <http://www.woodjohn.uk>
Rayleigh, Essex UK
On 2018-02-19 05:45, Scott Xe wrote:
Insulation resistance test is one of most common safety tests
nowadays: Flash test, earth continuity test, leakage current test
and insulation resistance test. Can someone share the history of
this teat to use DC and 500 V. The products are working on AC and
test voltage is higher than normal operating voltage but much
lower than the flash test. It is a trend to skip this test on
production line. What are the distinct benefits for this test?
Thanks and regards,
Scott
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