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@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