The only negative voltage I have ever ran into in telecom has been the –48 VDC.
Of course you used to have +/- 15 for RS-232.
Some –5 on the old PC power supplies, no idea where it was used.
I have never seen any other negative voltage used outside the chassis of
equipment.
Telecom originally was +48 volts until they started using underground and
buried cables.
With the ring side of the line grounded at the C.O. and the tip side of the
line powered with +48 any fault in the insulation of an underground or buried
cable allowed copper ions to leave the wire as electrons were entering. It
would corrode the wire into nothingness and copper plate the surrounding dirt.
So they swapped polarity grounding the tip side and putting –48 on the ring
side. The ions would then transport from the environment to the wire thus
plating it with who knows what, but the copper was still intact.
From: Forrest Christian (List Account)
Sent: Thursday, November 09, 2017 12:04 PM
To: af
Subject: [AFMUG] Negative Voltages...
I'm working on some support for -48VDC in various products.
I'm wondering if anyone has encountered a different negative voltage than
-48VDC in the wild, say -24VDC or similar. The main reason why I ask is that
it is looking like I'm not going to be able to support as wide of range of
voltages on the negative side as I do for the positive side (12-60VDC), and
wondering if I really only need to support something along the lines of
32-60VDC on the negative side.
--
Forrest Christian CEO, PacketFlux Technologies, Inc.
Tel: 406-449-3345 | Address: 3577 Countryside Road, Helena, MT 59602
forre...@imach.com | http://www.packetflux.com
