Tram Conduit Offset from Centre?

[littletorelate]

A possible newbie question, but very intrigued and can't see reference on Google...

I saw this pic on Twitter of a London conduit system tram on Westminster Bridge...

http://londontopia.net/wp-content/uploads/2013/08/794f4f72023a3ca82807efa241f1c8af.jpg

It appears to show the power conduit offset slightly from the centre of the running rails. Whereas most pics of London trams show it in the centre, as here (also on Westminster Bridge)...

http://stories-of-london.org/wp-content/uploads/2013/04/On-Westminster-Bridge.jpg

Is this correct or just an optical illusion? Seems unlikely to be an illusion given its alignment with the headlight of the tram in the pic.

If correct, what was its history and motivation (seems odd not to put it in the centre, unless to get round a patent issue for example?) Did it cause compatibilty issues with centre conduits?

Very intrigued.

Thanks in advance.

 

[theageofthetra]

The conduit would often be slewed over towards the outer rail where the line approached/left a plough change pit. But I wouldn't have thought there was one to the south of Westminster Bridge?

 

[edwin_m]

Definitely offset on the track nearer the centre of the road, and probably not offset on the other track. I wonder if there is some of the bridge structure that prevents it being centred? Or perhaps the running rails were re-aligned for some reason and the conduit was left alone.

Google just found me this page which shows how the conduit could be offset on interlaced track:

http://dewi.ca/trains/conduit/oddities.html

The same site includes photos of change pits, showing that the conduit was only offset for a fairly short distance.

Interesting also to note the tramway going against the traffic flow with no road markings or other safety measures visible!

 

[John Webb]

The plough was supported on a 'bus-bar' at each end and moved sideways on them to allow the plough to be inserted and removed, as well as give some flexibility in positioning as the tram moved along. But I must admit I'd never seen before the conduit off-set as much as the photo shows.

 

[Peter Mugridge]

OP, your second picture shows the offset on the other track as well as the centred one on the nearer track. Very interesting, and nice picture finds as well.

 

[CatfordCat]

E R Oakley's history of the LCC Tramways (Vol 1, p. 218) mentions this, and yes it was due to the bridge structure - "the 'bridge ribs' were partly in the way" leading to the conduit being offset on this section. The drains and mud pits (unseen bits of the conduit system) were also specially designed for this section.

I hadn't noticed this in photos of Westminster Bridge before...

And Blackfriars Bridge had similar - for similar reasons - photo here

And to answer the questions of practicality, the plough could slide freely along the plough carrier - and at a change pit would just slide off the end of the plough carrier without needing to be disconnected from anything.

 

[littletorelate]

Interesting, thanks. And thanks CatfordCat for the pointer to the book, which I've found in Winchester Library's railway collection.