OK so this actually work related but it has me stumped.
The IT unit at a school has new wiring (1 year old) and on one work
station bench there are about 12 or so computers and monitors all
powered the same ring circuit.
Each double socket powers one computer and its associated monitor.
It has been discovered that when you unplug or plug in a monitor that
sometimes some of the other monitors (either to the left or right of the
monitor that is been plugged and unplugged) lose their display for a few
I have checked the circuit and it is fine.
One other bit of info. The slower you plug or unplug the monitor seems
to make this happen more often.
I can go back in for another look if anyone wants any more info. My job
was only to confirm that the circuit was safe but I like a mystery.
 So the school closed the IT room for H&S reasons.
Presume by "unplug" you mean the power lead, rather than the
Do the monitors have external power bricks, or just an IEC mains lead
direct to the screen?
If they have bricks, do they do it when when brick is unplugged from the
monitor, or just when the brick is unplugged from the mains? Do they do
it when the monitor it powered on/off by the front panel button?
Are they no-name or branded monitors?
To answer an earlier response. We stopped using master switches for banks
of computers in classrooms when the computers started blowing their PSUs.
If you turned of 30, only 25 would come back on. After a short while the d
ealers wouldn't fix em under warranty.
Sounds like some sort of interference from sparks disrupting the signal
integrity. I presume they are all on digital interfaces these days?
Does it also fail if you plug and unplug an anglepoise lamp or similar
60W load that isn't one the monitors.
I presume you have eliminated the possibility of loose wiring in the
various sockets on the ring main (and/or it not being a proper ring). A
better quality of interconnect between PC and monitor might fix it.
Be worth checking that there is a proper earthing arrangement too.
Why are things getting plugged and unplugged though? Less wear and tear
to switch off at the wall or have a master off switch for them all.
My favourite in the days of tube based monitors when mobile phones were
new and exciting was watching the screen go crazy as the phone woke up
when it was about to ring and accept a call. It gave about 3s warning.
I'd say the same. We once had a set of desks here where one monitor
continually flickered after we replaced the PCs. We eventually found an
IEC lead on an adjacent monitor (plugged into the same PDU) had a
rewireable plug (rather than a moulded one) with loose screw
connections. I'd imagine if it was a higher wattage appliance it would
have got hot.
I am imagining that somewhere buried below you might find one of those
"smart" extensions which powers down when the current draw from a
specific socket goes to zero. They had a brief vogue when people were
mixing all sorts of kit, and just switching the PC off would also power
down printer, monitor, scanner, speakers etc etc.
The fact it's a school is suggestive. Just the sort of institution to
mandate such kit as part of a "green" initiative.
On Wed, 20 Sep 2017 11:59:26 +0100, Andy Burns wrote:
Meanwhile, chez Jethro, 4-way extensions have become a standard feature.
I cannot believe the hours I have spent scrabbling around behind
furniture to access a plug in a room - notwithstanding the usual plug/
appliance ratio problem.
Not sure where inspiration came from, but about 10 years ago bought a
bulk of 1m 4-way extension leads. Plug into a socket in a room and -
presto ! You've got access to moveable power. Since the biggest thing
that is ever plugged in is the hoover, I feel we're quite safe.
Cheaper than fitting 4 more double sockets (all of which would be full
now anyway). Just have a rule that we never plug another adapter into an
It's one of those "how on earth did I not think of it before" ideas.
Although pricing may be an issue. IIRC last time I bought "an" 4-way lead
it was a pack of 3 for £10 - cheaper than the 3-way cube adapters (which
I have junked).
I leave almost everything plugged in all the time
and only have a few of the 6 way individually
switched ones in a few places like where I brew
so I can turn lights plugged into it and brew
heaters etc on and off individually.
But all the lights will be Philips Hue soon,
so I wont need that for them either. Same
with stuff like brew heaters, that will be
wifi controlled now too.
I normally use the ones that come with the device
with the bigger stuff like tablets and phones and
charge the other stuff like the bluetooth headsets
from the PC with multi USB hubs.
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