Quick Question: London Overground Pantograph

[maxmarshall]

Hi Guys!!

I hope your week's are going well

I just moved into a new apartment and it happens to be above a London overground station.

I've noticed the trains have clean roofs at the front and the end of the train, but dirty roofs in the middle; It appears to be only around their pantographs (i believe that's what they are called?).

Do you think this is just caused by dirt on the wires being deposited onto the roof? or is it more curious that that: e.g. something involving the electricity transfer?

Best,
Max

 

[Bald Rick]

It’s a combination of the carbon residue coming off the pantograph, and (probably) because the cleaning doesn’t go near the pantograph for obvious reasons.

 

[Class172]

Likely to be carbon coming of the contact region at the top of the pantograph. I believe it's a graphite strip that is designed to wear over time, whilst providing a low friction conducting surface.

EDIT: Bald Rick has beaten me to it

 

[Jturner98]

I can confirm it’s definitely the carbon from the pantograph head. As part of the exams we do on the trains we have to clean all of that off around the pantograph well (gap in the roof) to check for damage. That carbon stuff goes everywhere, every time I go up on the roof it’s all over my trousers!

 

[maxmarshall]

Thanks for the fast responses! super interesting thank you

That's pretty crazy that carbon gets distributed so far across the roof (and no doubt across the tunnel ceilings too I guess?). That's got to be at least a 2-3m distribution.

Do you know how often the carbon elements have to get replaced, and their cost? It seems like a lot of wear and tear! Is the same true for all pantographs?

 

[transportphoto]

To avoid confusion, and I know it’s likely a simple mistype, no London Underground trains have pantographs - instead taking their power through a third and fourth rail. The issue as described above is likely to be replicated on any stock with pantographs anywhere!

 

[pdeaves]

From my viewing, it appears that the roof isn't that dirty, it's painted darker to hide the dirt. Also, strictly, it's not Underground it's Overground (but easy to confuse the two if you are unfamiliar with the subtleties of TfL branding and contracts).

 

[maxmarshall]

Haha now you have me questioning the paint! wow I didn't even notice that, let me see if i can notice any other passing trains that show a better indication of paint vs. dirt! Thanks

And yup it's definitely overground; I titled the video and [update: I realised I titled this thread incorrectly so I updated it- apologies!].

Yeah I think you're right!!! it looks roughly painted on the carriages around the pantograph, I guess to reduce maintenance. That's cool! thanks for the insight guys

 

[Domh245]

From my viewing, it appears that the roof isn't that dirty, it's painted darker to hide the dirt.

I'd think it unlikely. You could see that during the 5 car extensions, the 5th car (inserted between pantograph end and adjacent driving car) had a lovely clean roof having not been run under the wires for the same length of time, when it could have been delivered pre-painted

eg:

You can also look to other OLE units such as the 387s where the top of the front ends of the units are caked in dust, including over the high level marker light.

 

[norbitonflyer]

The roofs of London Trolleybuses were painted brown (instead of red as on diesel buses) for similar reasons

 

[maxmarshall]

I'd think it unlikely. You could see that during the 5 car extensions, the 5th car (inserted between pantograph end and adjacent driving car) had a lovely clean roof having not been run under the wires for the same length of time, when it could have been delivered pre-painted

eg:

You can also look to other OLE units such as the 387s where the top of the front ends of the units are caked in dust, including over the high level marker light.

That's the curious thing though, it's not the front end, only the middle. The front roof is as clean as the back.

RE the paint: if it is paint, then have they deliberately painted on the gradient that can be seen in this photo?

 

[Domh245]

That's the curious thing though, it's not the front end, only the middle. The front roof is as clean as the back.

That'll be down to the much lower speeds that the overground runs at compared to other services. For a given height between the pantograph and the roof, if a train is travelling faster it'll move further along the length of the train than if it is moving slowly - Compare the roughly 10m spread from your photo, to the 100mph unit where it covers over the length of one vehicle from the pantograph (20m), or even a 125mph Pendolino where there can still be appreciable levels of grime getting on for 50m away from the pantograph!

This screenshot also shows one of the other factors in how this grime falls - aerodynamics. It is much more pronounced in the leftwards direction, when the pantograph in question is the leading one. The reduced falloff to the right comes from when the pantograph is the rear one, and in a much larger aerodynamic wake. Not so much of a factor again on the overground with the low average speed though

100mph Class 700


125mph Class 390 Pendolino:

 

[pdeaves]

RE the paint: if it is paint, then have they deliberately painted on the gradient that can be seen in this photo?

On the other hand, if it's not paint and just dirt, why the hard edge as seen in this screen grab from approx 12 seconds? Perhaps some are painted and others aren't?

 

[Domh245]

On the other hand, if it's not paint and just dirt, why the hard edge as seen in this screen grab from approx 12 seconds? Perhaps some are painted and others aren't?

If you're talking about the hard edge on the left hand side of the picture, that'll be where an HVAC module has been (fairly recently) replaced on the train, and doesn't have the same build up as the rest of the roof. The photo in post 11 shows a similar effect with the module immediately to the right of the pantograph having a lighter coating than the surrounding roof!

 

[Jturner98]

I can confirm that the roof of the 378 is all the same colour. Light grey. The dirt on the roof is from the pantograph head carbon.

== Doublepost prevention - post automatically merged: 22 Apr 2022 ==

Thanks for the fast responses! super interesting thank you

That's pretty crazy that carbon gets distributed so far across the roof (and no doubt across the tunnel ceilings too I guess?). That's got to be at least a 2-3m distribution.

Do you know how often the carbon elements have to get replaced, and their cost? It seems like a lot of wear and tear! Is the same true for all pantographs?

Don’t know about the cost but the pantograph carbons are replaced it’s the whole head that’s replaced. Whenever the carbon has sufficient chips or is under 6mm in thickness