On 20 Sep, 20:19, Dominic wrote:
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.
Dominic

Isolation of the system, with all conductors insulated from Earth,
won't prevent electric shocks, because there is always some leakage
through the insulation, it only takes a few milliamps to get a shock,
and less than an amp to kill. 'Electrical Seperation', as the IEE
Regulations call it, is only effective on small installations.