Bars erupting from OHLE structures parallel to the contact wire

[Ken H]

On some OHLE structures sometimes there is a short bar that comes out of the supporting mast about the same height as the contact wire.
They are about a foot long. They look like someone has drilled a hole in the mast and welded or bolted this bar to the mast.
What are they for? Best guess is a lightning conductor of some sort.

 

[mcmad]

Sounds like a DEP, designated Earth(ing) Point. Used to connect the (hopefully turned off) OLE system to earth when maintenance works are happening.

 

[swt_passenger]

Is the reason they stick out the way they do to allow the earth straps to be put in place using long reach tools from ground level?

 

[Ediswan]

I believe this video show usage. I recall watching it out of interest. It does not seem to be working today for me (audio only), but others may have more luck.
https://safety.networkrail.co.uk/04_application_and_removing_earths-2/

 

[kentuckytony]

Just FYI - audio only for me.

 

[Ken H]

Thanks for the answers.

 

[Pigeon]

The URL of the actual video file is http://safety.networkrail.co.uk/wp-content/uploads/2016/04/04_Application_and_Removing_Earths.mp4

Download it to the hard disk and then play the downloaded file with a standalone player. It works fine, with both sound and picture.

Don't try and play it straight off the site in the browser. That just introduces a whole load more different possible ways for things to go wrong. Which particular thing is going wrong for other posters I cba to try and find out, but it's a turdpress site so it's not surprising that things don't work.

 

[Falcon1200]

IIRC, before DEPs were introduced long earths were often used, between the OLE and a rail, therefore blocking the line; DEPs allow the line to remain open for diesel traction. Not that that will always be practical of course !

 

[Ken H]

I used to commute from marston gren to five ways around 1990. The down freight line through Adderley Park was just taken out of use and the OHLE was earthed with big red cables. Don't remember what the earth end was attached to. Prob a DEP.

 

[swt_passenger]

If anyone cannot see the video animation, here’s a screen grab from the animation showing a clip on earth connection being made between two earth points across an insulator. The other point explained in the video is that at the ends of an earthed section two of the cables will be fitted in parallel, another reason for the spigots to be a reasonable length.

 

[SouthStand]

Why would you need duplicate earths?

 

[swt_passenger]

Why would you need duplicate earths?

It didn’t seem to explain exactly why, just stated that the end points of an isolation each got doubled up, with intermediate positions only having single straps.

 

[Nottingham59]

Why would you need duplicate earths?

I would imagine that is because, if they are ever needed, the deadly voltage will come from outside of the Earthed section, so the Earthing wire at the end of the section will carry the most current to ground?

 

[aleggatta]

Just thinking back to my HV training (a while ago now) and normally on insulators you have an arc gap provided by a metal probe. One end is connected to the earthed end of the insulator, and the other points towards the live end of the insulator, so in the event of poor conditions (heavy mist etc) where the air becomes more conductive, there is a designated flash point, to prevent damage to the rest of the structure. My guess is that there might be similar arc points fitted to structures where OHLE runs past to provide this functionality, so if there is a failure, it occurs in a controlled way?

 

[Pigeon]

Why would you need duplicate earths?

Belt and braces and sewing your trousers to your shirt.

 

[najaB]

Why would you need duplicate earths?

If you mean why would you ground at either end, I would assume to guard against voltage being introduced at either end. If you mean why two earthing conductors at either end, in case one falls off/gets caught.

 

[snowball]

May not protection also be needed against induced voltages if other lines nearby remain live?

 

[najaB]

May not protection also be needed against induced voltages if other lines nearby remain live?

Going to hazard a guess that's why the intermediate DEPs are also isolated.

 

[HSTEd]

Duplicate earths will also reduce the fault impedance if the line is accidentally reconnected to the supply whilst they are attached, increasing the fault current - which may allow the circuit breakers to operate more rapidly and reliably.