UL 1778 and EN50091-1-1 require backfeed testing which is almost identical to capacitor discharge testing. If a UPS has approvals, there is no hazard available(required to be less than 30VAC after 2 seconds). The test is also done while faulting the transfer relays(this makes sure that the manufacturer detects the possibility of the hazard and indicates a UPS failure and does not expose the user to the hazard). For Europe, the test duration is 1 second and they even specify very stringent spacings for the transfer relays(reinforced insulation between UPS output and power cord pins). I don't believe that any sort of warning is necessary. The standards do not make us put these kinds of warnings on the UPS.Yes there is a little energy left, but it has discharged by the time you remove the plug and actually touch the pins. On older UPS(pre 1992?) this was not properly addressed so perhaps you have heard about problems that have since been eliminated(we are very aware of this issue as we are involved with the standards organizations and we have helped to develop this requirement based on our own observations) Please realize that my opinions are of course biased as I work for a UPS manufacturer.
Please respond to [email protected] To: [email protected] cc: (bcc: Steve Williams/SDD/NAM/APCC) From: [email protected] on 08/17/99 08:43 PM GMT Subject: UPS Hello all, I was wondering if anyone had a comment on the following: Most uninterruptible power sources (UPS) have a unique characteristic. There exists an "energy" (albeit small) on the outlet plug prongs even when the unit is not connected to the mains supply. I have been told that it won't "Bite" you (~3ma @ 30-60vac) and that this is "caused by the continuous neutral incorporated in the unit which is required by UL". Although it may not be "dangerous" by the letter of the law, my concern is that if someone should unknowingly receive this "tingle" the natural reaction is to pull away which has potential for injury. First, is this the "norm"? and How should a manufacturer of a piece of equipment which incorporates a UPS warn their customers of this? Anyone have experience with this? Thank you in advance, Lisa --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
