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Class 373 braiding on the bogie?
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Elecman
Established Member
Definitely for earthing
driver9000
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- 13 Jan 2008
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Earth strap.
I'd say it's an earth strap. It seems to connect the body (top connection) to the bogie (middle connection) and the axle box earth return assembly (lower connection) - that's the item to the right of the lower loop of braid. The axle box earth return assembly looks like the type where three spring-loaded brushes touch a circular conductive plate that's fixed to the axle end. The axle box earth return assembly will be insulated from the axle box itself, often in a non-obvious way. This is about providing a reliable very low resistance bond between vehicle body (and the bogies) and the wheels and so the running rails, without any possibility of current passing through the axle box bearings. This ensures that if an overhead live wire comes down and touches the vehicle body the current goes safely straight to earth (the track) without any unsafe voltage appearing on the body where someone might be touching it, and can't cause hidden damage to the bearings.
Traction current returns will usually be formed of insulated cables going to similar types of axle box earth return assembly. In the case of a 25 kV ac loco the transformer 'earthy' (neutral) side will be connected via an insulated traction current return bond. Similarly on DC supply systems through the current rating is usually much higher. Again you must make special effort to force the current to flow where you want it to - as electricity has a nasty habit of flowing where you don't want it to!
I took the photo below of one axle end of 99001 at The Greatest Gathering. In this case you can seen the bogie-to-axle earth strap (lighter coloured cable) and the traction return (grey cable) connecting to the bottom of the same axle box earth return assembly. Again, that assembly will be insulated from the rest of the axle box assembly to guarantee that the return or earth current goes straight into the axle - wheels - rails without passing through the axle bearings. [note some of the cables on this photo, the ones with adhesive supports, are for test purposes]
Particularly on older EMUs return current and earthing is often done through brushes mounted on the cannon box or other part of the drive train, the brushes touching special brush tracks added to the axle assembly. In this case you wouldn't seen them easily.
There's never just the one of these, usually a minimum of two of each type of return are provided, more often nowadays one each per axle to ensure a high degree of redundancy.
Traction current returns will usually be formed of insulated cables going to similar types of axle box earth return assembly. In the case of a 25 kV ac loco the transformer 'earthy' (neutral) side will be connected via an insulated traction current return bond. Similarly on DC supply systems through the current rating is usually much higher. Again you must make special effort to force the current to flow where you want it to - as electricity has a nasty habit of flowing where you don't want it to!
I took the photo below of one axle end of 99001 at The Greatest Gathering. In this case you can seen the bogie-to-axle earth strap (lighter coloured cable) and the traction return (grey cable) connecting to the bottom of the same axle box earth return assembly. Again, that assembly will be insulated from the rest of the axle box assembly to guarantee that the return or earth current goes straight into the axle - wheels - rails without passing through the axle bearings. [note some of the cables on this photo, the ones with adhesive supports, are for test purposes]
Particularly on older EMUs return current and earthing is often done through brushes mounted on the cannon box or other part of the drive train, the brushes touching special brush tracks added to the axle assembly. In this case you wouldn't seen them easily.
There's never just the one of these, usually a minimum of two of each type of return are provided, more often nowadays one each per axle to ensure a high degree of redundancy.
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