Hi, Colleagues:
0) I would like to
share a personal experience of a different setting to offer an
angle for looking into this puzzling topic.
1) During my graduate
study, I was doing microwave experiments in the laboratory. On a
six foot bench, I had a series (maybe a dozen or so) of
waveguide components (made of metal, either solid copper or
silver plated) connected together as the test bed. With a half
dozen or so equipment attached to them at various points to
serve as the energy source or sink as well as detection
instruments. The setup exhibited randomly and unpredictable
behaviors. After awhile, my advisor brought up the topic of
"Ground Loops" that could introduce the interference in
mysterious manners. This is a phenomenon whereby minuscule electric current flowing along
metallic parts (even though they may appear to have no
"resistance" in between) that are connected to the system
common potential reference (the "ground") via slightly
different paths. These could be very small resistance path
between two points or high resistance leakage source. The
resultant electric potentials among the subsystems of
interest could be significant enough to
affect the outputs of sensitive instruments.
2) After much
cut-&-try, including plugging all instruments into the same
electric extension strip with no avail, I finally floated the AC
power cords of all instruments (using three-to-two prong
adapters) but kept only the most sensitive node in the system
connected to the AC power source "ground". Although this was
against the electric safety code, I finally got consistent
results. With clear record of the configuration, I even could
take the waveguide setup apart and then reassembled days later
to repeat the same results. Years later, I applied the same
philosophy to a smart-meter PCB design which got a better
precision than the chip manufacturer's demon board could.
3) So, it is possible
that the site with the reported "PoE induced" issues may be
somehow experiencing the above related phenomena. This kind of
situations are almost impossible to duplicate at another site.
It has to be diagnosed with pains-taking detective efforts, such
as inserting isolation subsystems suggested by one colleague.
Since this phenomenon takes a month or so to show up, discipline
and patience are the virtue.
4) On the other hand,
a product that can build up certain "memory" of the disturbances
like the above and to the point of requiring periodical power
cycling to flush clear the issue is definitely a sign of defect
design, based on my old school training.
Regards,
Abe (2022-03-31 10:40)
On 2022-03-30 15:57, Joe Greco wrote:
On Wed, Mar 30, 2022 at 05:52:06PM +0000, Livingood, Jason wrote:
Their crappy equipment needing rebooting every few weeks, not ridiculous.
Their purchasing gear from incompetent vendors who cannot be standards
compliant for PoE PD negotiation, tragically plausible.
Many customers buy their own cable modem. You can lease an Xfinity
device as well and those function pretty nicely these days but YMMV.
But typically a device reboot is a way to quickly solve a few
different kinds of problems, which is why techs will often recommend
it as an initial step (you can generally assume that there's data
behind what occurs when any one of tens of thousands of support reps
suggesting something to a customer - support at scale is data-driven).
No one's doubting all of that -- support is best when data-driven, scale
or otherwise. But that's actually the issue here. There's no data that
I know of to suggest widespread PoE ghost current buildups, and, given
the audience here, no one else has popped up with a clear "me too".
PoE is typically negotiated by modern switches, 24v Unifi special
jobbies aside, so it's all DC on cables that are already handling
differential signalling.
He's got graphs showing it every 24 hours? Liar, liar, pants on fire,
lazy SOB is looking for an excuse to clear you off the line.
Could well be from noise ingress - lots of work goes into finding &
fixing ingress issues. Hard to say unless we look in detail at the
connection in question and the neighborhood node.
No doubt. There's huge amounts of room for problems to be introduced
into last mile networks. But, again, this isn't about general problems.
This is about a tech claiming it's due to PoE, and that he's seen it
often before.
I certainly have a lot of sympathy for cable techs, but that doesn't
mean I want to swallow any random garbage they want to blame issues on.
Please just tell me it's the chipmunks getting feisty and nibbling on
the copper if you want to feed me a line...
... JG
