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Questions for the rail enthusiast

What are the yellow discs for?

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I.M. OUTAHERE18/09/2020 02:57:54
1468 forum posts
3 photos

20200918_114035.jpg20200918_114029.jpg 20200918_114035.jpg

I was waiting at a local rail station today a0nd spotted these yellow ( presumably metal) discs on the power lines , they are on the last 50m of a dead end siding and was wondering what purpose they serve ?

Any ideas?

They would appear to be around a 300mm or 12 inches in diameter


Juddy18/09/2020 08:57:21
85 forum posts

Just a guess but it appears that they maybe indicating the end of the powered section of the overhead line, it looks as if there are insulators just the other side of the yellow disc inline with the cables.

Grenville Hunt18/09/2020 09:38:14
26 forum posts

I think it may be an OHL tension indicator, overhead lines and catenaries expand and contract at different rates due to temperature fluctuations and the device indicates the effectiveness of the end of line counterbalance weights, the upper part of the disc is connected to the support catenary wire the lower to the OHL conductor.


I.M. OUTAHERE18/09/2020 10:47:58
1468 forum posts
3 photos


This is the real 3rd picture i intended to post so looking at the pictures in the original post except the bottom one as it is the same as the top one they are taken from right to left.

The first pic is showing the line furthest away far right end , the second is the far right or the closest line and the one in this reply is showing the left end of both lines lines .

The ends of the siding are offset lengthways and if they were both the same the length the discs would approximately line up with each other .

I couldn’t see any other discs on the main lines only on this little dead end siding .

So there are two discs per line equally spaced with each other in regards to each line and its end point .

Bazyle18/09/2020 11:11:07
6042 forum posts
220 photos

On the weekly EDMES coffee morning zoom call our railway expert believed they are some 50yds from the changover point between power sections to warn the line crew that they are going to a section that might not be turned off or at a different voltage.

They might also be used to indicate sections that are different construction, such as the special areas where the west country combined diesel and electric engines can raise their pantograph at 80 mph ready to turn off the diesel. If they do it on the ordinry sections the impact of the pantograph at high speed rips the line down.

I.M. OUTAHERE18/09/2020 11:45:21
1468 forum posts
3 photos

Forgot to mention this is in the western suburbs of Sydney Australia .

The rail gauge is as far as i know consistent throughout New south Wales Australia .

They are on a now disused siding consisting of two dead end lines about 300m off a set of points , i think they may have used this siding hook up a couple of diesel locos to help the intra state passenger trains or freight trains get over the blue mountains - could and probably am wrong though !

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