‘Crossing’ OHLE - threading right to left

[Bayum]

As you’re travelling under OHLE, every so often, you come across sections where overhead wires cross from the OHE mast to the contact wire and back to the OHE mast. Is it a way of keeping tension? Earthing sections of wire?
An example is on this video from 09:32:

(Video is of a steam train front view from Peterborough to Southall)

 

[hexagon789]

As you’re travelling under OHLE, every so often, you come across sections where overhead wires cross from the side away from the track to the centre

They are designed to do that, they deliberately weave side to side to even out pantograph head wear. If they didn't a groove would be worn into the middle of the collector head.

 

[stuu]

The contact wire isn't continuous, it's made up of lengths of wire which are swapped over at intervals, with an overlap between them. The individual wires are usually fixed at one end and have either weights or springs to maintain the correct tension at the other end, off to one side of the track

 

[edwin_m]

They are designed to do that, they deliberately weave side to side to even out pantograph head wear. If they didn't a groove would be worn into the middle of the collector head.

It's known as stagger. On straight track alternate supports will pull the wire in opposite directions, but on tighter curves the curvature means the wire slides across the pantograph between the support and the midpoint.

 

[hexagon789]

It's known as stagger. On straight track alternate supports will pull the wire in opposite directions, but on tighter curves the curvature means the wire slides across the pantograph between the support and the midpoint.

Thank you, I couldn't for the life of me recall the proper term and Google was no help!

 

[snowball]

Stagger, as discussed in #2 and 4, happens between every pair of consecutive support points (masts). My impression is that the OP was asking rather about the less frequent arrangement discussed in #3, where one tension length of wire ends and the next begins.

 

[zwk500]

@Bayum, is your first post complete? There are a number of interesting questions you might ask about overlapping wire lengths and the challenges they pose.

 

[stuu]

You can't see the stagger of the wire from on the train, unless you are the driver

 

[Beebman]

There's a very authoritative 376-page publication 'Overhead Line Electrification for Railways' last revised in 2021 by Garry Keenor which should answer any questions about OHLE. It's available as a free download although the author would appreciate donations to the Railway Children charity. This is the URL for the download page (it's a 179 MB PDF document):

https://ocs4rail.com/downloads/

 

[Bayum]

@Bayum, is your first post complete? There are a number of interesting questions you might ask about overlapping wire lengths and the challenges they pose.

I’ve just checked it and the last half has disappeared!

 

[swt_passenger]

You can't see the stagger of the wire from on the train, unless you are the driver

Also, in addition to that key point, the stagger is all but continuous on straight track. It doesn’t just occur ‘every so often’, so I believe the OP is asking about the wire run terminations

 

[Bayum]

Sorry, everyone. I’ve edited my post to what was originally typed but only half of it was posted.

 

[zwk500]

As you’re travelling under OHLE, every so often, you come across sections where overhead wires cross from the OHE mast to the contact wire and back to the OHE mast. Is it a way of keeping tension? Earthing sections of wire?

https://www.bathnes.gov.uk/sites/de...ng/nr_a_guide_to_overhead_electrification.pdf is an excellent overview.

In short, the wires are in short lengths (1-1.5km IIRC) to maintain tension as the temperature changes. On some systems, the tension is maintained by ratchets, pulleys and weights that are mounted to a stanchion on the edge of the line (see wikipedia article for piccies). The wires crossing from the edge to the centre will be the beginning of one wire length, and then the wires crossing back out will be the ending of the previous wire length. Different scheme designs can use different tensioning equipment which may allow in-line or perpendicular wire length terminations rather than needing to move the wire out of the line gradually.

 

[Taunton]

You can't see the stagger of the wire from on the train, unless you are the driver

Apart from noticing above adjacent tracks that the suspension arrangement from the masts to the wire are alternately from the left and from the right.

 

[Pakenhamtrain]

We call it an airgap in Australia.

We define it as:
Airgaps are formed by overlapping contact wires and catenaries
at the beginning and ends of tension lengths where the
conductors are taken to the tensioning devices or fixed anchor.

 

[edwin_m]

The length of each wire section is limited by the amount of expansion the tensioning equipment can cope with, but also by the maximum size of the drum the wire is run out from. It would be a bad idea to introduce a weak point by splicing the wire.

 

[AdamWW]

You can't see the stagger of the wire from on the train, unless you are the driver

Or it's a loco hauled train with the pantograph at the rear of the engine and decent windows in the end doors.

Gives you a very good idea of how the stagger works.

 

[stuu]

Or it's a loco hauled train with the pantograph at the rear of the engine and decent windows in the end doors.

Gives you a very good idea of how the stagger works.

How many of those are there in the UK?

 

[snowball]

You can also often see stagger in photographs or videos taken from overbridges.

 

[swt_passenger]

You can also often see stagger in photographs or videos taken from overbridges.

I think possibly the best thing to do to see both the stagger and the details of wire run terminations is to watch a good cab ride video.

 

[Signal Head]

As you’re travelling under OHLE, every so often, you come across sections where overhead wires cross from the OHE mast to the contact wire and back to the OHE mast. Is it a way of keeping tension? Earthing sections of wire?
An example is on this video from 09:32:

(Video is of a steam train front view from Peterborough to Southall)

It's an Overlap, where two tension lengths, er, overlap at their ends. In direction of travel, the arrangement transfers contact to the 'incoming' wire, the two sections then run together for a short distance, before the terminating wire (apparently) rises slightly off the pantograph and out to the anchor.

In older type of OLE (eg WCML), there were 'insulated' and 'non-insulated' overlaps. At the non-insulated ones the two sections are just bonded together, the insulated type are provided at Booster Transformer locations, where the sections are connected via one winding of the transformer. I presume they are also used where a manual section switch is provided.

 

[D6130]

There is about a quarter of a mile of OHL with no stagger on the Down Shipley between Armley Junction and Armley canal bridge. This is because, during electrification works in the mid-1990s, it was discovered that the tall cutting retaining wall on the Down side - to which the OHLE cantilever structures are attached - was found to be only partially load-bearing and the possibility that the stresses from either the push-on or pull-off arms (I forget which) could risk a partial collapse.