Insulated fences beside electrified railways

On my travels outside Victoria I’ve noticed something curious whenever I see an electrified railways – insulated fences.

Set K82 arrives into Circular Quay on the City Inner track

I’ve spotted them up in Queensland, where they use the 25 kV AC electrification system.

'Isolation gap' notice on a platform fence at Gympie North station

I’ve spotted them over in Adelaide, which also adopted the same voltage for their new electric trains.

Timber poles provide an insulated gap in the metal fencing around the electrified Seaford line rail corridor

And I’ve noticed them in Sydney, which uses the same 1500 volt DC system as Melbourne.

Insulated fence panel beside the railway at Bowenfels

And curiously, on the Sydney Light Rail, which uses 750 volt DC power for traction.

Insulated fence panel at the Arlington light rail stop

The reason for these insulation gaps is safety – if the overhead lines that power trains fall to the ground, the last thing you want to happen is the entire railway station become live, and electrocute any passengers who happen to be touching a metal object! By providing insulated gaps in metal fences between the ‘trackside’ and ‘station’ sections, this risk is reduced.

Back in Melbourne, I’ve never seen an insulated gap in our station fences – only jumper cables between the overhead stanchions and the running rails.

Grounding jumper between stanchion and running rails

And grounding connections between the tram fences and the tram tracks.

Electrical grounding connection between a platform stop fence and the tram tracks

It makes me wonder – why doesn’t Melbourne have insulated gaps in the metal fences around out railway lines?

Some recent developments

About five years ago Melbourne started adding some new.

Plastic shrouds installed to insulate overhead stanchions at East Camberwell station

Insulating plastic shrouds around overhead stanchions on station platforms.

Plastic insulating cover on an overhead stanchion at Bonbeach

I wonder what the driver for their rollout was?

Further reading

The Transport for NSW Asset Standards Authority (ASA) has published Guideline on Earthing and Bonding at Railway Stations that explains the safety issues further.

At railway stations, three main types of risks may exist:

1. Risks associated with 1500V DC stray leakage or fault current.
2. Electric shock risk due to 1500V DC touch & step potential rise under fault condition
3. Electric shock risk due to high voltage/low voltage distribution systems’ touch & step potential rise under fault condition

There is a possibility that overhead wiring structures may rise to a potential above earth. The risk of persons receiving an electric shock when standing beside an overhead wiring structure and touching the structure is present and is of concern.

Other hazardous situations where persons could receive an electric shock is when physical contact is made by touching overhead wiring structures at the same time as they touch lighting poles, metallic parts of canopies or awnings, steel troughing, metal fences or rolling stock.

In order to minimise these risks, methods have been developed and deployed for the overhead wiring system.

As well as a document detailing the specifications for insulation panels found in their fences.

Insulation Panels

Insulation panels, a minimum of 2200mm in length, are required in metallic fencing in the electrified area to break the fence up into short electrically isolated sections. The panels consist of the fence material with supporting posts that are non-metallic. The panels are installed where ‘continuous’ fencing:

  • would otherwise approach within 2.0 metres of an OHW structure (including any metallic attachments to the OHW structure such as switch handles, back anchor guy rods etc)
  • would otherwise approach within 2.0 metres of station fences, foot bridges, rail bridges, entrance fences and metallic buildings
  • runs parallel to, and within 2.0 metres of, above ground metallic signalling/cable troughing or air lines. The insulating panels must be located directly adjacent to the insulated joint in the signalling/cable troughing or air lines
  • meets any high voltage substation fence (either RailCorp or local electricity distributor). Where the substation earth mat extends outside the substation fence, ‘continuous fencing must not enter the area of the earth mat.
  • meets any pole mounted or pad mounted substation (either RailCorp or local electricity distributor). The ‘continuous’ fencing must not enter the area of the earth mat. The continuous fencing must also not be closer than 2.0 metres from exposed substation metal fittings.

Insulation panels are to be installed:

  • to ensure that persons cannot contact ‘continuous’ fencing and any other metallic service such as OHW structures, station fences (associated with the station low voltage earthing system and water pipes) and footbridges that extend outside RailCorp property,
  • at approximately 300 metre intervals in the ‘continuous’ fencing (with a maximum spacing of 800m in areas away from above ground signal troughing).

The non-metallic posts shall have a clearance of minimum 50 mm and maximum 100 mm from the adjacent metallic post of the ‘continuous’ fencing. Each non-metallic post must have a warning sign attached as shown on the drawing.

The bottom rail shall be installed so as to remain 80 mm clear of the ground.

Security and High Security Fences

When installing security and high security fencing, the fence shall be designed and positioned so to reduce or eliminate the requirement for insulation panels. Where insulation panels are required and can not be avoided, they shall be of a design that complements the high security performance of these fence types.

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11 Responses to “Insulated fences beside electrified railways”

  1. Mike says:

    I thought those panels were to stop people climbing the lattice poles. Are you sure that they are for insulation?

  2. Beren says:

    Overhead power lines have tension in the form of a column of heavy blocks. The snapping of the line causes it to shoot away. It’s highly unlikely for the cable to touch the ground. Its suspended from the overhang by many small strands. The worst you’ll get is it hitting a pantograph.

    There are two pieces to this, the hanging line and the suspended portion.

  3. Andrew S says:

    You can add Perth in that list with isolated panels of fencing along the rail corridors. Melbourne is quite different from Sydney and Perth in that track side fencing along suburban lines is extensive rather than the ad-hoc and mostly recent works in Melbourne.

    From a joint council PTA job on a Perth suburban station they were worried about stray induced currents in just about anything which slowed right down design and construction among many other concerns. Might give a hint as to why the Metronet projects are only starting now when the next WA state election in in March next year.

  4. Thede3jay says:

    A lot of new projects use perspex panels to create an insulated gap in the fencing. Maybe have a look out for those, especially on some of the level crossing removal projects.

  5. Liam says:

    This is curious, electrical substations typically bond everything, perhaps those who did rail electrification in Victoria were thinking the same way?

    Some of the train overhead in Victoria is shared with 66kV sub transmission lines. A few years ago near Glenferrie a bat bridged one of them to the metal structure. The bond was either in poor condition or missing, so the fault current went through a signal lamp…

  6. Tony Taylor says:

    A while back, and it’s probably still an issue, earth links were being pinched from substations. I wonder if the thieves would be prosecuted for manslaughter if someone was killed because of incomplete earthing.

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