I believe that part of the reason for this is that there are differences in contact wire tension on these systems i.e. the higher the speed - the higher the wire tension.
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My point was that they perform on both systems (all in the case of the 373s) using the same pantographs. I've also seen a photo of a train on the ECML passing over a level crossing with its pantograph almost straight - at least my memory recalls it that way! However,
http://www.rssb.co.uk/Library/stand...ry/2013-Strategic-direction-CR-HS-ENE-TSI.pdf B1.2 states 'All rolling stock required to operate on the GB AC 25kV 50Hz sub- system that has not been upgraded in accordance with the HS-CR ENE TSI, the following requirement shall apply:
Pantographs shall have a working range of 2100 mm. When mounted on an Electric unit, the pantograph shall operate between 4140 mm (the lower operating position, ref. EN50206-1, 3.2.13) and 6240 mm (the upper operating position, ref. EN50206-1, 3.2.13) above rail level.'
That's one hell of a difference!
At C1.11 of the same document it goes on to say: 'The contact wire height on Eurotunnel infrastructure in the Channel Tunnel varies between 6 020 mm and 5 920 mm.'
By my calculation that means that UK contact wire height can be higher than the Eurotunnel system wire height.
Over to you, forum members, to add to this (or correct it!).