I am going to jump into this frey, here is my 2 cents... In the case of Medical Electronics, if the fault condition would cause more exposure of radiation to the patient than what was "dialed in" (X-Ray, MRI, Ultrasound) that would be a BAD thing. End of subject. dave garnier
From: Lou Aiken [mailto:[email protected]] Sent: Tuesday, January 28, 2003 11:00 PM To: peter merguerian; [email protected] Subject: Re: Circuit Breaker Tripping Dring Fault Tests Here is what I think the requirements are: If the product remains safe, within the meaning of the standard, and the branch circuit overcurrent protection device does, or does not, operate as a result of fault testing, internal overcurrent is unnecessary. If the product does NOT remain safe, within the meaning of the standard, as a result of fault testing, internal overcurrent protection IS necessary, branch circuit overcurrent protection is inadequate, and internal overcurrent protection is necessary. Safe within the meaning of the standard: Does not exceed allowable fault temperature limits, does not catch fire, enclosure does not deform to the extent that parts involving the risk of electric shock or personal injury become exposed to the test finger or probe, will pass the required electric strength test after the fault, etc. IN order to be confident that the design is safe one must continue the fault testing until steady state conditions exist, OR for the maximum clearing time (for the resulting fault current) as stated in the standard for the particular overcurrent device. It is incorrect consider the result acceptable when the overcurrent device opens the circuit. The overcurrent device should be removed from the circuit and the current monitored during the fault test. Only approved fuses and circuit breakers should be specified if they are necessary make the product remain safe - within the meaning of the standard. There is a significant difference in the endurance and clearing limits between the UL and IEC standards for fuses and circuit breakers with the same current rating. Lou Aiken, LaMer LLC 27109 Palmetto Drive Orange Beach, AL 36561 USA tel ++ 1 251 981 6786 fax ++ 1 251 981 3054 Cell ++ 1 251 979 4648 ----- Original Message ----- From: peter merguerian <mailto:[email protected]> To: [email protected] Sent: Tuesday, January 28, 2003 1:54 PM Subject: Circuit Breaker Tripping Dring Fault Tests Dear All, For safety, it is not clear from the standards whether the main branch circuit breaker tripping during fault conditions is an acceptable result. I see no reason why this should not be acceptable. What is your view? Some third party labs find it acceptable and others do not. Anyone can lead me to some inernational decisions regarding this issue? Thanks, Peter _____ Do you Yahoo!? Yahoo! <http://rd.yahoo.com/mail/mailsig/*http://mailplus.yahoo.com> Mail Plus - Powerful. Affordable. Sign up < ttp://rd.yahoo.com/mail/mailsig/*http://mailplus.yahoo.com> now
