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J.Lombard
User Rank
Silver
Re: Same Issue
J.Lombard   9/20/2013 10:32:54 AM
NO RATINGS
Tekochip,

I am curious as to what type of leakage test you are referring. Is this a chassis Hi-pot test for AC leakage to geround or something performed at a lower voltage? We do a Hi-pot from the AC mains connection to the metal chassis, but disconnect the AC/DC power supply to prevent damage to the power supply from the 2200VAC test voltage. The test is performed to meet CE Low Voltage Directive safety requirements. We trust the CE mark by the manufacturer on the power supply is sufficient to exclude the power supply itself from the high-voltage stress. 

AJ2X
User Rank
Silver
Re: Definitions
AJ2X   9/20/2013 9:04:13 AM
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I'd second the idea of an article on grounding.  I've been an engineer for 30 years, and just about every time I've worked with separate grounds in a system it has gone badly.  Mostly I've worked on television cameras (commercial and medical), and keeping all the grounds tied together (usually through the chassis) has been consistently the most successful method for reliable results, both in EMI (which has always been a design concern) and signal integrity. 

But I've also heard time and again that you should keep chassis and signal grounds separate, so it'd be really interesting to know what I've been doing wrong (or right) all these years.  There must be a way to pass the EMI tests and avoid the ground noise horrors described in the article.  You're never too old to learn!

mrmikel
User Rank
Iron
Re: Definitions
mrmikel   9/20/2013 8:51:14 AM
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There can be huge amounts of energy in frame grounds.


A printing company I did some work for had their parking lot repaved. The grounding mat for the printing equipment was underneath and they broke it.


They were blowing out electronics left and right in the 480 volt system.


In an existing installation it can be no small matter to avoid tying the electronics and frame grounds together.

TJ McDermott
User Rank
Blogger
Definitions
TJ McDermott   9/19/2013 7:52:56 PM
NO RATINGS
Mr. Lombard, this was a terrific article.  It could be the beginning of a two or three part series covering Ground, DC Common, AC Neutral, and Earth.

tekochip
User Rank
Platinum
Same Issue
tekochip   9/19/2013 4:31:08 PM
NO RATINGS
John;

 

I had the same issue with an LCD display and had to isolate its frame in order to pass our own leakage testing.

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