GWR ATC on DC Electrified Llines

[Belperpete]

Does anyone know what happened with GWR ATC when a loco was running on a fourth-rail electrified line? It would clearly be undesirable for the ATC shoe to come into contact with the juice rail.

I have done an internet search, and found something about an extra indicator in the cab of locos that ran on LT lines, to show that the ATC shoe was locked up. But I am not clear how the shoe would be raised/locked. Was there a control in the cab to raise the shoe? A lever or valve? Or did the driver have to go trackside to raise the shoe?

Were there ever any cases where a driver forgot to raise the shoe, or a loco with the standard ATC shoe accidentally ran onto LT?

I am presuming that nothing special was needed on third-rail electrified lines, as theoretically the shoe should never come into contact with the outside juice rail.

 

[30907]

Can't answer about the practicalities, but it would have been a frequent occurrence, as all 4 platforms at Paddington Suburban were electrified.

 

[randyrippley]

biggest risk would presumably be freight over the North London and maybe West London lines?
Were WR locos allowed over the NLL?

 

[pdeaves]

Did the ATC ramps sit higher than the power rail? If so, that might mean there was no problem at all.

 

[Bradshaw]

They had to be clipped up, this link explains
http://www.railsigns.uk/sect12page1/sect12page1.html

 

[Belperpete]

They had to be clipped up, this link explains
http://www.railsigns.uk/sect12page1/sect12page1.html

Thanks for that.
Were all GW locos fitted with automatic clipping-up, or just those that worked over the fourth rail areas?
And any idea how the shoes were unclipped when a train left the fourth rail area? I am presuming that the unclipping would have to be either automatic, or controlled by something in the cab, as it would be impractical for every train leaving Paddington suburban to have to stop for the driver to unclip the shoes.
And was there anything to protect against a train inadvertently continuing on with the ATC shoes clipped up, and hence the ATC disabled, if the unclipping failed? Or was the driver just expected to notice at the next distant signal that the ATC wasn't working?

 

[Taunton]

Thanks for that.
Were all GW locos fitted with automatic clipping-up, or just those that worked over the fourth rail areas?

There did need to be a modification, which was only done to the 61xx tanks, the 97xx condensing pannier tanks, and later the Pressed Steel dmus. All others were not permitted in the "Suburban" side of Paddington. Presumably this had to be applied to previous generations of GWR suburban locos as well, such as the County 4-4-2T locos. There was an additional indicator in the cab which showed the shoe position. There must have also been a protective fuse in the ATC equipment just in case negative -210 volts actually got applied to what was low voltage equipment.

I, too, have never understood how the ATC reverted when they left Paddington.

I also don't know what happened on the West London line. WR locos certainly ran down here in the 1950s (and right through to south coast resorts), but before 1939 this had been 4th rail electrified for the ex-LNWR electrics which ran Willesden Junction to Earls Court suburban services. Were GWR locos not allowed then?

Does anyone know what the voltage was in the GW ATC ramp. It didn't have any warning signs around it for track staff, but must have been enough to go through the loco circuits and ring the bell in the cab. If it was the same voltage as track circuits, using the same battery arrangement, that would make sense. It was a positive voltage, but a modification to (some) GWR main line locos on the Paddington-Reading main line later allowed them to give a double hoot when a 4-aspect signal was at double yellow, this was done by a negative voltage, instead of the usual no voltage for a distant at caution. Locos without the modification would give just the normal caution hoot.

Birmingham to Paddington expresses could be delayed in foggy conditions on the Bicester-West Ruislip section, where they would otherwise run at full speed, by LNER etc trains ahead, without the equipment and groping slowly along.