Great Western Coffee Shop

From Wikipedia (https://en.wikipedia.org/wiki/Torquay_Tramways) and https://www.tramwayinfo.com/trampostcards/Postc102.htm


Wikipedia goes on to talk about the various issues with the system, but could this not provide a future solution for the people of Bath, even though they had trams with overehead collectors in the past?   Is there scope for third rail lines to be only energised as trains pass over them, and could that somewhat help the safety case for (for example) electric trains from London to Salisbury?

We have been here before you know - most recently when "here" was Nice (http://www.firstgreatwestern.info/coffeeshop/index.php?topic=22283.0). I thought there were some other places the topic had come up - either for trams alone or the same idea on trains - but can't find any now.

The stud contact system was also used to power trams in London.
It was expensive and unreliable.
A magnet mounted under the tram turned on the power to each stud. The power was collected via a skate supported on springs under the tram so as to make a sliding contact.
Sometimes the power was not turned on and progress thereby delayed.
Sometimes the stud remained live which could kill pedestrians or horses. To reduce the risks, an extra "detecting skate" was fitted at the rear of the tram, if this passed over a still live stud a warning bell alerted the driver who was instructed to stop and affix a rubber cover over the still live stud. By the time the driver reacted, stopped, and alighted to affix the insulating cover, the tram would have moved some yards. Any pedestrian crossing the road behind a departing tram was at risk. In wet weather the road surface near a live stud reached a dangerous voltage. A following tram was liable to dislodge the insulating rubber cover, with potential fatal results for horses and persons. Surviving humans and horses learned to avoid stepping on the studs.

Unreliable and dangerous, soon replaced by overhead wires.

I doubt that anything similar could be used on conductor rail routes. Too complex and expensive, and still some risk of electrocuting trespassers.
Better in my view to use battery power for short gaps in existing conductor rail electrification, and 25 KV overhead for longer gaps. Dual voltage stock is readily available.

Thanks for that linkage - there is indeed "nothing knew" and the knowledge and memory of our members is so valuable in joining up our knowledge base!

The main ground pick-up system used in London was conduit - lots of it, in use through to closure. Studs were chosen where the local council refused to allow overhead wires, because it was much cheaper than conduit. There were several systems, and while others were given limited trials (e.g. off-road) in London, only the Griffiths-Bedell system was chosen for a real installation on the Mile End Road. It worked for 23 days - so not a success, but politics had almost as much to do with that as practical experience.

This G-B system was the one where the studs were flush with the road until the magnet pulled them up, making them live via an internal switch. So when the alarm bell rang to indicate a stud was still live behind the "skate", the driver was meant to bop it on the head with a rubber mallet. Being London, there is more about this then other installations - such as this quite detailed report (https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwi82anB8tH1AhWLXsAKHaXCAYUQFnoECAgQAQ&url=http%3A%2F%2Fwww.tramwayinfo.com%2Ftramways%2FDownload%2FGBstud.pdf&usg=AOvVaw0tVqPUdewvlPYecf8n-qhg).

From my copy of Simmons's book, the main systems used in Britain were:
Lorain (Brown) - Wolverhampton
Dolter - Paris*, Torquay, Hastings (plus Mexborough and Swinton)
G-B - Lincoln, London (briefly)

*Diatto was the main Paris system, and Simmons may have got that wrong. I think it was used in Brussels too. But both had mainly conduit where wires were not allowed.

On conduits, Brittannica (1911) says:

That's wrong - one merit of the system was the greater ground clearance of its skate, and the studs were at or below ground level, but didn't move. The skate was made of a row of blocks hung from springs and were pulled down onto the stud. A rubber hammer was still involved, to make the the armature under the stud pull back into its "off" position.