Automation Canada - Cables & Connectors Issue - 15

While field testing for DC resistance unbalance is technically optional,
it is highly recommended for PoE installations. And don't be fooled by
DC resistance unbalance specifications on a vendor's cable - DC
resistance unbalance is more often caused by poor workmanship such
as exceeding maximum bend radius, not maintaining pair twist as close
to the point of termination as possible, or not terminating each
conductor consistently. While conductor termination consistency can
be easier to achieve when using a multi-wire punchdown tool (plus it
can ease hand fatigue), field testing for DC resistance unbalance is really
the only way to ensure performance for PoE after installation. Thankfully,
there are now industry testers on the market that allow you to easily add
DC resistance unbalance testing to the mix. The tester screens below
shows testing results for DC resistance unbalance on individual pairs
(PAIR UBL) and between pairs (P2P UBL).

Testers are available that test DC resistance unbalance on individual
pairs and from pair to pair.
THE RIGHT TOOL TO TROUBLESHOOT
Even if you've certified the cable plant and did the recommended DC
resistance unbalance testing, things can still go wrong - especially if
C A N A D I A N A U TO M AT I O N

the PSE and PD are not compatible. Knowing the class of the PSE and
the PD is the first step to troubleshooting PoE. Unfortunately, not all PSE
and PDs have the Ethernet Alliance marking, or the mark may not be
easily accessible or visible. A PD may be located up to 100 meters away
from the PSE back in the telecom room, and you need to check the class
of both to know if they're compatible. Furthermore, if you're checking
multiple PDs, they may not necessarily be powered by the same PSE.
Even if the PSE and PD do end up being compatible, there could still be
a problem with the cable itself. You could waste half a day just tracking
the cable and accessing the PSE.
One way to ease this process, is to use a troubleshooting tool
specifically designed for PoE. These tools are cost-effective and easy to
use, allowing you to simply plug into an outlet at the PD location to find
out if it's connected to PSE and what the specific class of power is on the
link to ensure if will support the device. Some of these tools will even
identify the data speed on the link, as well as length, potential cable
breaks or other failures - all right there from the device end.
While you may be new to PoE, it doesn't have to be complicated and
you can easily ensure your installations go smoothly by including DC
resistance unbalance in your certification testing and choosing the right
troubleshooting tool.

Mark Mullins is one of the founding members
of Fluke Networks, starting in 1993. He has been
involved in all of the key areas of the business,
including cable testing, network troubleshooting
and analysis. He currently oversees the
company's Global Communications efforts,
keeping customers and prospects up-to date on
cable testing products and technologies. As a
member of the Ethernet Alliance Marketing
Committee, he is responsible for promoting the
Gen 2 Power over Ethernet Certification
program. He holds a B.S. in Computer Science
and an MBA from the University of Washington.

VOLUME 3, ISSUE 2

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https://www.fluke.com/en-ca

Automation Canada - Cables & Connectors Issue

Table of Contents for the Digital Edition of Automation Canada - Cables & Connectors Issue

Automation Canada - Cables & Connectors Issue - 1
Automation Canada - Cables & Connectors Issue - 2
Automation Canada - Cables & Connectors Issue - 3
Automation Canada - Cables & Connectors Issue - 4
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