[asterisk-users] Polycom power over ethernet (PoE) cables for 500/501, 600/601 and 650 sets

[Stephen Bosch]

Hi, folks:

I just took delivery of new PoE cables (PN 2200-11077-002) for our
Polycom phones here in the office.

I have the following to report, for the erudition of existing Polycom
users and those considering purchasing Polycom sets from the set of
models noted in the subject:

1. The cables do indeed work (hooray).

2. The cable has a module on it about a third of the way from a female
end. The module is about the size and shape of a large cigarette lighter
or a small bar cellphone; it has a green LED indicator on it, which
illuminates when the connected device is drawing power. The module also
has a receptacle for the DC end of a Polycom power adapter. Presumably
these cables can replace the default external AC injection cable completely.

The module, for those who are interested, provides ground-loop detection
and protection. Early revisions of the 802.3af standard did not provide
for ground-loop protection in the midspan, and so phones would overload
(and fry) PoE midspans (this is strong evidence that there were no
telecom engineers in the 802.3af working group, since ground-loop
protection has been a necessary part of PSTN systems since the dawn of
time).

I suspect newer midspan equipment is not burdened with this problem,
which would explain why some people can use garden-variety cables with
these phones on PoE.

3. I thought I might save some clutter by putting these cables between
the midspan and the patch panel, but then I discovered that the male end
of the cable is keyed, just as in the default AC cables provided with
the phones, meaning that they'll only work if plugged directly into the
phone itself. The reduction in clutter with this set-up is,
unfortunately, not what I had hoped, though anything is better than
nothing. I imagine it would work if I sanded away the plastic post on
the connector, but that says nothing about how it might behave if a
non-compliant device were plugged into it. Better safe than sorry.

Cheers,

-Stephen-