Thicknet/10base5 Test Segment: The Cable is In!

[Bill Gunshannon]

On 06/28/2018 01:22 PM, Liam Proven via cctalk wrote:
> On Thu, 28 Jun 2018 at 18:45, Eric Smith via cctalk
> <cctalk at classiccmp.org> wrote:
>> In case it may not be obvious to some readers, the reason you should NEVER
>> ground an Ethernet cable (of any kind) at two points is that the ground
>> potential at two different points is unlikely to be the same, so that will
>> cause a DC current flow through the cable.
> I installed the first LAN at the biggest builders' merchants in the
> Isle of Man, some 28 or 29 years ago in my first job.
>
> Normally, we'd have wired it too, but they said no -- we have staff
> electricians, we'll put in the cabling, you just connect it. So we
> gave them the specs, they fitted benches, ran in lots of 13A 220V
> power, thinwire, plus plentiful power sockets & breaks in the cable
> for every position.
>
> We hooked up the PCs, installed the server, installed the DOS
> networking client, and started testing.
>
> It worked. We left.
>
> Within days, I was back. Intermittent dropouts -- basically, at more
> or less any given time, one machine couldn't see the rest of the LAN.
> But which one changed every few minutes.
>
> Much testing. At software level because we were a small company, in a
> small island nation, and Ethernet testers were _way_ over anyone's
> budget.
>
> Basic continuity worked. I started testing each node. All worked
> individually. So I started bisecting the thinwire and checking each
> half.
>
> I got a shock. Off a thinwire cable.
>
> I had a voltmeter, at least, and it was registering a 3-digit number of volts.
>
> I think I actually did say the full unexpurgated WTAF.
>
> The Ethernet wasn't grounded -- most weren't -- but it *was* lying in
> the same conduit as the new mains cable, many dozens of metres of it.
> AFAICT the mains cables were _inducing_ current in the Ethernet. Quite
> a lot of it.
>
> The client had to rip out and relay most of the cabling. They were
> ignorant enough to be overconfident: wires are wires, we do wires,
> we'll do them like any other wires and it'll be fine.
>
> What amazed me is that none of the NICs blew, none of the machines
> failed or died. Once the cabling was sorted, it was OK. Who knew that
> BNC Ethernet ports could handle 100V or more flowing through them and
> mostly work?
>
>
>

The US Electrical Code has not allowed any kind of signal wire in
the same conduit with any kind of power wiring for as far back as
I can remember.

bill