Rationale for electrically connecting sections of metal fence together?

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Electric-Light

Senior Member
I noticed the sections of metal fences on local light rail(+750v DC overhead catenary with rail return) platform are connected together with moderately heavy gauge jumpers.

The fencing is only there to prevent people from falling into/jaywalking across the rail.

What purpose does it serve to connect each section together with jumpers?
 

hurk27

Senior Member
I noticed the sections of metal fences on local light rail(+750v DC overhead catenary with rail return) platform are connected together with moderately heavy gauge jumpers.

The fencing is only there to prevent people from falling into/jaywalking across the rail.

What purpose does it serve to connect each section together with jumpers?

My best guess is to provide a equal potential between all metal parts, I would also expect that somewhere down the fence line there is a bond to the grounding system of the power supply for the rail, of the grounded rail conductor.
 

cadpoint

Senior Member
Location
Durham, NC
I saw the same thing on DC metro's rail service!

My thought is they know when the fence has been damaged in any manner, they send a continual or pulse signal down the line to know exactly where they have a problem if the fence has been physically altered and thus braking the signal! They do the same thing with high voltage lines to know exactly where a break occurs in the service!(ok, so I've heard)
 
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CONTROL FREQ

Member
Location
OHIO
I saw the same thing on DC metro's rail service!

My thought is they know when the fence has been damaged in any manner, they send a continual or pulse signal down the line to know exactly where they have a problem if the fence has been physically altered and thus braking the signal! They do the same thing with high voltage lines to know exactly where a break occurs in the service!(ok, so I've heard)

I've heard of the same kinda thing! Worked a couple weeks with a guy from ADT security. He told me that he was involved with installing a system around some "big movie star's house" and the fence was insulated from the ground during installation so that a low V signal could be sent across the fence. Anytime the fence was touched by something/someone touching the ground with their feet SUPPOSEDLY, an alarm would let the inhabitants know of a possible security breach! Sounded crazy to me---BUT so did communicators when I watched 'star trek' as a kid. Now that I have a cell phone, I'm just waiting for 'TRANSPORTERS"!!!:cool:
 

ohmhead

Senior Member
Location
ORLANDO FLA
Ground

Ground

Well its called touch potential they do that in most power plants they only place i have seen sensors for a fence was a state prison project we did once and that was called a g -line . So my best answer would be if you have a high voltage around its a ground simple as that .

Also the prison had sensors every 10 foot if you applied 50 lbs on that section of fence it set off a alarm turned on the floods on that section only nice and bright the main console had a fence computer graphic screen which then flashed on that 10 foot section . funny but your not getting out 18 foot with razor wire on top in a 4 foot roll then a double fence outside that one 20 foot apart with a five foot deep footer under fence on each . The g- line was if you came near top of fence a magnetic field would pick you up if you were thinking about flying over it .
 
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broadgage

Senior Member
Location
London, England
Here in the UK it is the normal practice to bond together all metalwork in the vicinity of electric railways, not just fences but also hand rails, lighting columns, metal footbridges, advertising hoardings and pretty much anything mettalic on or close to railway property.

I believe that the reason is to avoid dangerous voltage appearing between say two metal fence sections, or between a lighting column and a handrail.
There is the small but real risk that the overhead wires could be brought down by accident and touch nearby metallic articles.
In such cases, it would be desireable to have all nearby metallic articles bonded with substantial conductors in order to limit voltage differences that could otherwise be dangerous.
Lighting columns, metal fences and the like are are of course in contact with true earth, but the resistance to true earth of a single item would be relativesly high.
By connecting together numerous such items, a very low resistance to true earth is obtained, this should result in a substantial fault current that will promptly open protective devices.
 

Electric-Light

Senior Member
I saw the same thing on DC metro's rail service!

My thought is they know when the fence has been damaged in any manner, they send a continual or pulse signal down the line to know exactly where they have a problem if the fence has been physically altered and thus braking the signal! They do the same thing with high voltage lines to know exactly where a break occurs in the service!(ok, so I've heard)

It's definitely not tamper detection. Each section of fence is connected at the bottom with bare stranded wire jumpers that looks like they're at least 3/8" around.

Rails run in the middle with roads on outside and each stop is setup as an island.

I've seen the same thing on a metal chair at the platform station.

The fence is only 3' tall and the only purpose is to deter jaywalking and force people to walk 25' or so and use the crosswalk.
 

n1ist

Senior Member
Location
Massachusetts
Occupation
Principal Electrical Engineer
They did the same thing over at South Station in Boston when they electrified the Northeast Corridoor for Amtrak. Handrails, light poles, and even the the temporary shed scaffolding for the walkway by track 1.
/mike
 
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