Most AC/DC and DC/DC power supplies have input/output isolation and neither side of the output grounded unless/until you ground one side. If you ground the - side, then it's referred to as +48V. If you ground the + side, then it's -48V.
Fancier equipment with stuff like management interfaces may be dedicated as +48V or -48V, I have an Eltek Micropack system that can only be used as -48V. Lots of stuff from the telecom world may be that way. Something like a Mean Well power supply will almost certainly be floating until you ground one side of the output. I know a WISP guy who tends to power all his DC+fiber radios with individual AC/DC power supplies and doesn't ground them. I am a traditionalist and want all my power supplies ground referenced, but it seems to work for him. I guess you could argue it prevents ground loops. Where we typically run into problems is with the loads like radios and routers, sometimes they are floating and don't care, some have the + side grounded, some have the - side grounded. Chuck was probably saying to check with an ohmmeter from DC+ and DC- to chassis ground. I have also been lucky that when I got it wrong, it just popped a fuse and no magic smoke escaped. Hopefully you individually fuse all your loads. -----Original Message----- From: AF <af-boun...@af.afmug.com> On Behalf Of Mark - Myakka Technologies Sent: Monday, January 8, 2024 10:26 AM To: af@af.afmug.com Subject: [AFMUG] -48V kicking the dead horse I know we have been though this many times and I thought I understood it. -48VDC is the Negative side being HOT, correct? It is BAD to try to mix -48VDC and 48VDC There is no such thing as a -48V battery. A battery is a battery, correct? How about the ICT Platinum power supplies. They show as 48VDC, can they be used on -48VDC equipment? I remember Check saying something about a way to test to see if a piece of equipment that is Neg 48VDC is truly grounded as Neg 48VDC. -- Thanks, Mark mailto:m...@mailmt.com Myakka Communications www.Myakka.com -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
