Electrical safety on a LAN

  • Thread starter Thread starter Mike Saunders
  • Start date Start date
M

Mike Saunders

I have a requirement to introduce a pc into a LAN that is in a seperate
building to the rest of the network and server. I am aware that this is a
candidate for a wireless link but I would nevertheless like to know whether
it is a viable option to carry the network cable to the other building for
this purpose. As I recall there may be an issue with earthing that makes
this unsafe however I do know that both buildings share the same substation
if this makes a difference

Note this is in the UK

Many thanks


Mike Saunders
 
For electrical safety you'd need to consult with an electrician. Keep in
mind that the maximum distance for a single cable run without a switch or
hub in the middle is 100 meters, distance may be a larger enemy than
electrical problems.
 
if there is any question about ground differences or it is a long distance
you should consider a fiber optic link. the equipment is available off the
shelf and custom made cables are not that expensive.
 
I have a requirement to introduce a pc into a LAN that is in a seperate
building to the rest of the network and server. I am aware that this is a
candidate for a wireless link but I would nevertheless like to know whether
it is a viable option to carry the network cable to the other building for
this purpose. As I recall there may be an issue with earthing that makes
this unsafe however I do know that both buildings share the same substation
if this makes a difference
Click to expand...

Ground potential differences on the network cable degrade signal, but
aren't an electrical hazard as such.
Note this is in the UK
Click to expand...

Heck, you guys across the pond don't even wire buildings correctly,
how can you do LANs? :)

Distance and signal strength are your issues, not electrical safety.

Jeff
 
That search pulls up a good list of protectors. But
protectors are not same as protection. Protector is only as
effective as the protection it connects to. Notice a
dedicated grounding connectors on better protectors. A
connection made less than 3 meters and to the same, single
point earth ground that all other incoming wires connect.
Earth ground is the protection - the most essential component
in a protection system. Protector only makes the connection
to protection.

That other building is a perfect example of a big lightning
rod that may invite lightning to seek earth ground through
computer in this building. But if wire from 'that' building
first connects, through protector, to 'this' building's
central earth ground, then no problem. Any lightning hit on
'that' building is earthed before the resulting transient can
enter 'this' building.

How does the telco operate an expensive switching computer
during every thunderstorm without damage? They do same.
Earth all wires, via extremely short connection through a
protector, to the Master Ground Buss - the single point
ground. A protector is only as effective as its earth ground.

Some examples of protectors for RJ-45 type network wires
that can connect, less than 3 meters, to earth ground:
http://www.keison.co.uk/furse/furse19.htm
http://www.tripplite.com/products/product.cfm?productID=151
http://www.tripplite.com/products/product.cfm?productID=153#spec
http://www.keison.co.uk/furse/furse08.htm
http://www.keison.co.uk/furse/furse07.htm
 
w_tom said:
Earth ground is the protection - the most essential
component in a protection system. Protector only
makes the connection to protection.
Click to expand...

Then how do you explain the use of "protectors" on
airplanes where a connection to earth is out of the question?

Equipment damage occurs when high voltages arc across
unintended conduction paths and/or high currents burn
out normal conduction paths. It doesn't have much to do
with Earth except that lightning currents are frequently
trying to make a path to earth.

Suppose in the Tower Diner & Restaurant on the top
floor of the tallest building in town, which gets hit
frequently by lightning, you have your computer
equipment frames connected together through the
"grounds" in your surge protector power strip and
on the first floor you have the computer for the
reservations desk also on its own surge protector.
Further suppose they are connected together by CAT-5
10-BaseT Ethernet LAN wire. Then you might
want surge protectors near each end of your
10-BaseT wire with the protector grounds connected
to the surge protectors or to the frame holding your
Ethernet adapters. Connecting these surge protectors
to their own separate earth connection would be the
wrong thing to do, because then the protector grounds
would not be tracking the equipment grounds, during
a lightning strike and damage would likely be worse
than have no protectors at all.
 
This discussion was not about airplanes - was it. To
confuse or complicate the issue, a building protection system
is to be applied to an airplane? OK. In Japan, a 747 was
struck in the nose. Is that a complete circuit? No. Path to
earth ground is required. Strike continued out of tail into
earth. In this case, earth ground was the tail.

A Turkish Air Force 747 leaving Spain was struck in the
nose. Connection to earth ground was via left wing. This
1970s event was disastrous because something in wing was not
properly grounded. The resulting direct lightning strike -
cloud to earth - caused a failure in left wing due to
insufficient grounding. In this case, the earth ground was
tip of left wing.

IOW aircraft design gets more complicated because earth
ground (outgoing path of that transient) can appear anywhere
on plane. Therefore plane must be designed for a single point
ground that can be anywhere. No problem for experienced
aircraft designers. Too complex for this discussion group and
building protection. But again, protection is still about
shunting - diverting the transient. Something that
ineffective plug-in protectors fear you might learn.

Correctly noted is "damage occurs when high voltages arc
across unintended conduction paths..." Exactly why Ben
Franklin was so successful in protecting churches in 1752.
The technology of protection is that well proven - and
demonstrated in that previous posts. Nothing stops, blocks,
absorbs, or filters a destructive transient - no matter what
myth a plug-in protector would have you believe. Only the
naive associate a surge protector with surge protection -
using word association rather than science to make a
conclusion.

Again, look at effective protectors. A dedicated wire
shunts (diverts, connects) destructive transient to earth. No
mystery here. Same thing that Franklin did in 1752. Concepts
so well proven in 1930s research papers. Protection
demonstrated in virtually every town every year. Protector
only as effective as its earth ground.

Electronics atop the Empire State Building typically suffer
25 direct strike per year - without damage. Electronics atop
WTC suffered 40. Why no damage? Many of those 1930 research
papers specifically demonstrate the concept repeatedly - in
direct contradiction to anyone who thinks a surge protector is
surge protection. In each case, a destructive transient is
earthed - not absorbed or blocked. It is shunted to earth.
Electronics never suffer massive voltages because shunt make
that part of circuit (from cloud to earth) near zero volts.
Near zero volts is more than enough for electronic internal
protection to protect that appliance.

Effective protectors are called shunt mode devices. Why?
They don't stop, block, or absorb transients. In direct
contradiction to myths; they shunt - connect the transient to
earth ground. IOW only as effective as their earth ground.
No earth ground means no effective protection. Don't take my
word for it. A benchmark in protection does not waste your
intelligence on big buck warranty claims. Instead they
discuss effective protection - extensively. What do those
application notes discuss? Earth ground:
http://www.polyphaser.com/ppc_technical.asp
http://www.polyphaser.com/ppc_pen_home.asp

No earth ground means no effective protection.

Do 10-Base-T cables need protectors? Of course not.
Protectors are installed only when wire cannot make a direct
connection to earth ground. But 10Base-T can make a direct,
hardwired connection - using a ground block. Same applies to
CATV cable. Protector not required. But again, what is
essential to protect the 10Base-T? Single point earth
ground. Protection is the earthing point - not a miracle
protector. One is only fooling himself if he wishes an
adjacent protector was doing anything for that network. Look
at manufacturer's numerical specs. THEY don't even claim that
protection. Protector being too far from earth ground AND too
close to transistors.

Protector necessary when incoming wire (ie telephone, AC
electric) cannot make a direct earthing connection. What is
the one component always necessary to protect every wire?
Earth ground. Some wires protected by earth ground need no
protector - ie CATV and satellite dish wire. Others make that
connection through a protector (telephone). Again, John is
strongly encouraged to first learn and read about how
protection works in those so many Polyphaser application
notes. He is encouraged to find where plug-in protectors even
try to dispute this.

Concepts also demonstrated by this industry professional:

http://www.erico.com/erico_public/pdf/fep/TechNotes/Tncr002.pdf
How buildings may be earthed demonstrate in:
http://www.cinergy.com/surge/ttip08.htm
Concepts summarized in less technical text:
http://tinyurl.com/2hl53
http://tinyurl.com/l3m9

Read Polyphaser and Erico application notes. Visit their
protectors. Again, it is not about connecting to a receptacle
safety ground. Receptacle is not earth ground. Protection is
about earthing an incoming transient so that transient does
not overwhelm existing internal protectors found in all
computers and network interface cards.

Protector is only as effective as its earth ground which is
why plug-in protectors must avoid discussing what is posted
here - to not lose an excessively overpriced sale.
 
Back
Top