isolation of DC supplies for track work etc

[neilw]

Could someone offer me a brief explanation of the process involved for ensuring power is off before trackwork or similar commences, please? I have some old documents (60/70's) which seem to indicate that once the substation had turned the power off in an evening it was deemed OFF and was up to the p-way workers to check this was true using a box of eggs or similar. It stayed OFF until the appropriate line clear paperwork was completed but there didn't appear to be any earthing or SCD applied. These days, are permits to work issued and is the track earthed or shorted before such permission is given? Thanks in advance.

[zbang]

Generally.....

a competent electrical worker would-
check their meter for a proper reading
have the power feed turned off
pull a physical disconnect and put a tag/lock on it
check the rail voltage (should be zero)
recheck their meter that it works
put a earthing strap on the sections to be worked.

then add signing off clearances/permits/etc, and placing markers.
I assume that the TfL and Network Rail have their own (possibly conflicting) procedures.

(See also "Track Access Controller")

(IIRC, there was an RAIB report that detailed this, I'll see if I can find it)

[Tom]

The process is pretty much as neilw writes.

On LU, staff responsible for Protecting Workers on the Track in Engineering Hours (PWT-EH) must observe the last train, place their 'egg box' (a Current Rail Indicating Device) on the track, wait for the current to go off at or after the published time for current switch-off (the CRID lights go out), test it still works using the test button, then go on the track to work. If the current goes off early and a recharge is needed (or there's an incident requiring current off close to the normal switch off time), they mustn't go on the track, and this usually results in a big delay to everyone working as all the PWT-EH's have to be contacted to make sure they're not on the track.

Rather than placing earthing straps the re-energisation is managed by procedure; the staff concerned 'book out' with the Track Access Controllers and the PWT-EH for each group must check in at the end of the shift to confirm all their staff and equipment are clear of the track and it is safe for trains to run.

Only once each group in a current section have confirmed they're off the track can the current be switched back on in the morning.

In possessions it's more complicated, and this does involve the placement of shorting bars at intervals.

[philthetube]

It causes big issues if the power is turned off for other reasons around close of traffic.

Everyone who might be on or about the track has to be accounted for.

[neilw]

Mar 26, 2021 17:43:58 GMT Tom said:

The process is pretty much as neilw writes.

On LU, staff responsible for Protecting Workers on the Track in Engineering Hours (PWT-EH) must observe the last train, place their 'egg box' (a Current Rail Indicating Device) on the track, wait for the current to go off at or after the published time for current switch-off (the CRID lights go out), test it still works using the test button, then go on the track to work. If the current goes off early and a recharge is needed (or there's an incident requiring current off close to the normal switch off time), they mustn't go on the track, and this usually results in a big delay to everyone working as all the PWT-EH's have to be contacted to make sure they're not on the track.

Rather than placing earthing straps the re-energisation is managed by procedure; the staff concerned 'book out' with the Track Access Controllers and the PWT-EH for each group must check in at the end of the shift to confirm all their staff and equipment are clear of the track and it is safe for trains to run.

Only once each group in a current section have confirmed they're off the track can the current be switched back on in the morning.

In possessions it's more complicated, and this does involve the placement of shorting bars at intervals.

[neilw]

Could I ask Tom for a brief summary of the possession system please?