[PLUG-TALK] Hooray! Re: POE addendum

[Keith Lofstrom]

Reminder: POE (or PoE) is "Power over ethernet".

A followup about safely connecting wired ethernet to 
the Emporia VUE in my load center.

On Tue, Jan 06, 2026 at 09:34:42PM -0800, Keith Lofstrom wrote:
> 
> Today I purchased a small 4+1 port "SLRKIT" PoE switch for
> this purpose, mistakenly assuming it was PoE input/injection
> power for internal switch electronics only.   It actually
> uses PoE input power to feed PoE power to the 4 branch ports.
... 
> I will learn more from experiments; perhaps there is an
> isolating 48V DC-to-DC converter in that 2x3x1 inch switch.  

Indeed there is.  Experimental success! 

With benchtop 48V POE power into the SLRKIT uplink port, and
a POE camera plugged into downlink port 0, the three remaining
unused downlink ports 1/2/3 are still un-powered between
pair12 and pair36.  There is proper high impedance between
all 5x4 pairs.  The other POE ports power up only when there
is a POE load attached to them.  More watts conserved.

All SLRKIT pairs seem to be transformer coupled and isolated
from each other.  If 120V line voltage somehow shorts to one
of those ports, it won't pass through the SLRKIT device and
damage the other ports or the devices connected to them.

Pretty good for an $18 POE passthrough gigabit ethernet switch. 

Note that the POE injector driving the switch draws 2 watts
from the wall socket (as measured with a Kill-A-Watt meter). 
With a POE camera plugged into the switch, it draws 5 watts.
With two POE cameras, the Kill-A-Watt measures 7 watts.  

More precise measurement requires a Kill-A-Milliwatt. :-)

I still haven't had a chance to read the latest Oregon
Electrical Specialty Code book and learn whether a VUE or
an ethernet cable passthrough in a circuit breaker box
is permitted by code, but with the SLRKIT connecting the
ethernet cables, it probably CANNOT uplink lethal voltage,
even if wires abrade and short inside the load center.  

Keith L.

P.S.: The twisted pairs from the current sensors to the Vue
are kinda messy.  I could wrap them with Velcro ties, but
ordinary Velcro isn'willt plenum grade.  I ordered flame retardant
"cranberry color" FR/UL Velcro tape from levitthookandloop.com
in New York - $30.20 for 25 yards.   

P.P.S.  I have NOT found any Oregon vendors for FR/UL Velcro,
and most mail order vendors sell it by the 200 yard spool for
$$$.$$.  Enough to bundle a small data center.  I may need
only two yards of the 25 yard tape to neatly bundle the VUE
sensor wires and data cable.  I will trade the extra FR/UL
Velcro for sysadmin tips.

P.P.P.S.  My M.D. wife won't let me build a 100 rack data 
center, even it uses up 200 yards of FR/UL Velcro.  I won't
let her open a rabies ward.  Quid Pro Quo.

P^4.S.: POE is a global standard, compatible around the world.
Someday, there may be POE electric shavers for world
travellers, and POE bathroom sockets in hotels for them to
plug into.  No more travel adapters for different voltages
or plug configurations; a P.I.T.A. on a multi-nation business
trip.  Someday, POE smart shavers will order new cutters when
the old cutters wear out.  They might even test for skin
cancer and email medical record updates to your doctor. 
Let's hope that ugly haircut criticism can be disabled :-)

-- 
Keith Lofstrom          keithl at keithl.com