I'm having a hell of a time with UL. A piece of equipment I'm having tested is powered with -48vdc from the power grid in a CO. That power grid takes in AC from the street, steps it down to 48 VDC rectified, then passes it across the batteries, finally distributing it out to the racks in the CO.
That 48 VDC is SELV for there are fuses all over the place in the CO right up to where the equipment in the racks plug into it. Under UL1950 3rd Edition, Table 18, page 125, I'm declaring that the 48vdc is secondary and I asked to have my equipment tested operationally at 500V. I have had 48vdc equip tested at another lab and approved to UL1950 3rd Edition under the same claim above. UL says no way. It must be tested under the PRIMARY heading of Table 18 page 125. It is important to note here that I WANT the hi-pot testing to be done. Well, now I'm told that if I demand this to stay as I originally asked, then I only get UL1950 2nd Edition until the year 2000. I don't understand. I've had this done before without a problem. Also, the power supply people, more than one, find this to be news to them. Most of the hockey puck DC-DC converters out there (that I've dealt with) aren't able to withstand 1414VDC operational. Am I alone here? Are other mfrs of 48vdc and 24vdc equipment intended for COs running into the same thing??? Regards, Doug
