[NamTaf]

I'm not sure how this works for electrified rails (i.e. a third-rail that provides power to the engines), however for a standard rail line (i.e. just 2 tracks, with either an overhead providing electricity, or diesel engines) is used as a method of safety using the track signalling.

Specifically, in many rail signalling network systems, a signal will turn red when it detects a short between the two rails in its section (i.e. an axle rolls into it). It will then turn back green when that short disappears. Workers can therefore clip something between both rails, which triggers the signal relay and makes the signal light green.

This is absolutely not isolation & lockout though, because it doesn't actually remove the energy source. That's not to say it's not a valuable process though, but an isolation & lockout for this sort of circumstance either involves locking the track switches to direct traffic away from the worksite, or installing a derailer [1] on the track that phyiscally throws the train off the rail into the dirt so it stops well clear of the work site.

The above obviously doesn't work if you're working on a running system, though (which does happen, occasionally). In that instance, the track clip lets trains stop at the red light, radio to the worksite, have the worksite clear, then remove the clip, let the train through, then resume work. It's different levels of safety for different perceived risks.

[1]: https://en.wikipedia.org/wiki/Derail

[tialaramex]

Track circuit operating clips are used for the system you're talking about, they're just a pretty simple arrangement of giant spring clips with a deliberately short lead between them, workers are trained to apply the clips starting with the side away from the third rail, the lead is too short to make it possible to connect the third rail to the running rail if you've done it this way.

The big metal bar is different, as the poster explained it will short the (supposedly dead) power circuit in a third rail system, taking several hundred volts at quite a lot of amps until the short is detected, hence it can't just be a couple of metal clips and a cheap cable like TCOC. If some idiot re-enables power to the circuit or a fault elsewhere re-energises it despite it notionally being switched off, the bar will turn that into a full short and everybody will know there's a problem, although I'm not sure that would save anybody who happens to actually be touching the now surprisingly live rail at the time it's energised.

On overhead systems there is similarly an arrangement where a worker - after confirming that the power is supposedly dead - ensures this is true by physically grounding it. Again it's a failsafe.