As far as I understand, this requirement was needed in the time that insulation 
materials 

might have hygroscopic properties. Insulation materials as wood were common in 
the past.

If they were not suitably treated, in humid circumstances insulation might drop 
to unacceptable levels.

 

 

Gert Gremmen

ce-test qualified testing

((partially) retired in France)

 

From: John Woodgate [mailto:j...@woodjohn.uk] 
Sent: Monday 19 February 2018 10:46
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Insulation resistance test

 

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  <mailto:j...@woodjohn.uk> <j...@woodjohn.uk>
Date: Monday, 19 February 2018 at 4:22 PM
To: Scott Xe  <mailto:scott...@gmail.com> <scott...@gmail.com>,  
<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> <EMC-PSTC@LISTSERV.IEEE.ORG>
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 Associates 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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