In message
,
Dominic writes

On London Underground the DC traction current circuit to and from the
trains is via an insulated third live rail and an insulated fourth
live rail, and the earthed running rails are not used for traction
current. Would it be possible to use an isolation transformer to
prevent the electrocution of a person who touched one of the live
rails on this type of railway, or possibly on an AC version of it?
My understanding, which I am sure will be corrected, is that an
isolation transformer could prevent the electrocution of a person who
connected one live rail to earth, but would not prevent the
electrocution of a person who connected the third live rail and fourth
live rail together. I would be very grateful to anyone who can explain
further.

No.

Transformers won't work with DC so the whole system would first have to
be converted to AC to even have a chance of working. I suppose it would
prevent the risk of electrocution as no electricity would get anywhere
useful.

Then you have to decide what you are isolating from what? Isolating
transformers don't stop electrocution; they just reduce the risks in
certain circumstances such as faults to earth (which, of course, LUL
nominally doesn't have as it is a 'floating' system).

The main issue would be that you still need the potential difference
between the 3rd and 4th rails to drive a train. If your electrocutee
touches both of these rails there will be no difference than if it was a
train there and it will hurt - a lot!.

In short, if it had a hope of working it would have doubtlessly already
been done. The easiest way is to just keep people away from the nasty
electricity as in any similar situation involving high risks of death.

--
Steve Fitzgerald has now left the building.
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