Rich, is the below information true for both the AC and DC hipot methods? Some companies have contractors,subcontractors, incoming and final hipot... so it does and can occur at least 4 times, before its shipped to a customer. Richard,
From: Rich Nute [mailto:ri...@sdd.hp.com] Sent: Thursday, May 22, 2003 9:23 PM To: j...@jmwa.demon.co.uk Cc: emc-p...@majordomo.ieee.org Subject: Re: Safety testing after equipment repair Hi John: > > My last (3) employers have required all repaired or modified units to be > > "hi-potted". If a unit has been repaired, then the cover was removed, and > > the unit is no longer "controlled" by the oroginal production hi-pot. > > > > I think this is too stringent. Repeated hi-pot tests must be > *minimised*, because of the possibility of progressive degradation of > insulation. Yes, indeed, repeated hi-pot tests must be minimized. However, significant degradation of modern insulations at these low voltages and durations is doubtful for the lifetime of the equipment. Some years ago, I undertook a test to determine when an insulation would fail if subjected to a continuous hi-pot voltage. I connected several units to the hi-pot voltage for 8 hours/day. The units started failing after about 10 days. That would be about 48,000 minutes. So, we can say that we should probably not exceed 1/1000th of 48,000 minutes, 48 minutes, of hi-pot test time for the equipment lifetime. That would be 48 1-minute hi-pot tests. I don't believe any equipment would be so tested. Now, the transients are only 50 microseconds. 1.2 million transients would comprise one minute of degradation. As I recall, an industrial site would incur 5-10 such transients per day. That means, about 120,000 days for an accumulation of 1 minute of overvoltage. That's over 300 years. While repeated hi-pot tests must be minimized, the degradation due to repeated hi-pot tests is not likely to have an effect for the lifetime of the equipment. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc