Probably mostly plating with FE as there seems to be a lot of that around...
On 11/09/2017 11:51 AM, Chuck McCown wrote:
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
[email protected] | http://www.packetflux.com <http://www.packetflux.com/>
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