On 12/06/2018 5:47 AM, David McLoughlin wrote:
> When I saw this story on the ABC last night, my first thought was that it was nonsense, and that the "victim" had imagined it (such imagination is a common pyschological phenomenon).
> The "victim" wasn't even walking on the track, which is not part of the APS system anyway, and has no overhead wire. Any "shock" could not be related to the track.
> If there was an "exposed wire" anywhere, it could not have been a tram wire.
> Then I see Dudley has linked a similar piece from the SMH.
> The skeptic in me is crying "rubbish.
I am inclined to agree with you, but the article did raise within me thoughts about risk management with isolated return rails.
In traditional tramway construction (as in Melbourne) the rails are electrically connected to the ground (earth) - so they can't get much above earth voltage and you can't get a shock. Similarly structures like fences and overhead p[oles are bonded to rail and earth.
You can see an example at left of the attached pic - where an earth bond is attached to the fence.
When you insulate the rails from the earth - to prevent electrolysis through stray currents - then the rails will be at a higher voltage than the local ground / earth potential. It should be a small voltage and harmless and there will be safeguards to ensure this.
I wonder if during the construction phase some of these safeguards are not yet implemented?
I wonder what structures like fences are 'earthed to' in Sydney?
Mal Rowe - speculating and more given to a psychological / sensationalist reporting explanation