Thursday, November 19, 2015

Networking in Paradise...

Networking in Paradise...  In response to a reader's question: the network cable tester I have is the Fluke MS2-100, pictured at right.  It has a basic TDR (Time Domain Reflectometer) built in – no analog display, but it tells you the wire distance from the meter to any problem.  It detects opens, shorts, and pairing.  Having this thing in my toolkit has saved me hours of manual troubleshooting.  Just on this job I've used it to tell me exactly where three separate wiring problems were, and to verify that the complete installation is working correctly.  Highly recommended!

There's one other challenge to my networking here that I haven't mentioned before.  The cable modem and main router for my house are located in Debbie's second floor office, and powered from the house electrical power.  To get Internet in my shed, I've run CAT-6 all the way from that router out into the shed.  The challenge is that the ground wires on that Ethernet cable are using the house's power ground – and the shed (including the network equipment out there) is on its own ground (because it has a completely separate AC main, including it's own transformer and meter).

If you've ever done any utility-side electrical work, you can anticipate my challenge: it's the classic “ground loop” problem.  In my case, it's exacerbated by the fact that I have high current intermittent loads in the shed – things like a welder, 5 HP air compressor, etc.  If I tried to connect the house Ethernet to the shed Ethernet, I'm sure to have large transient ground loop currents between them – and quite likely fry some equipment!

The classic solution for this sort of problem is electrical isolation (between the house and shed, in my case).  I've never done this for Ethernet before (never needed to!), so I didn't know what was available.  It turns out that medical equipment with network connections routinely deals with this, and there are parts readily available.  I chose a Black Box SP426A “Ethernet Isolator”, pictured above left.  This is an optoelectronic device that's powered from the Ethernet line, very conveniently for me.  Mine should arrive tomorrow, and at that point I can actually install the router, switch, and wireless router in my shed...

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