TI21 tc's under electrification

[PJW]

I think the impression that TI21s are not used on ac electrification has resulted from the decision to use dc track on teh East Coast Main Line electrification (although the ones that were sthere originally such as Selby diversion were rertained). I think that the decision was based on costs; as has been pointed out there are some issues witth run round paths so the "first cost" expense was higher than originally had been anticipated. Given that this means block joints in high speed running line, I am not sure whether this was right decision for "whole life costs" but when trying to get the job done for minimum cost to get it to happen at all, sometimes one must make such decisions. The actual electrification was itself done on the cheap and has had to be strengthen since, to atttempt to keep the OHLE still in the air wind the wind blows.

There are lots of places with TI21 under the wires, including the GWML to Heathrow airport; indeed where there needs to be immunity to dc as well then really they are only option (apart from the HVI which are only suitable for jointe configuration and whose lengths are very limited- so much so that NR is now interested in the single rail Ebitack 200 - the digital development of TI21- as an alternative to HVI over switch and crossings)

TI21s are used all over the place in AC and DC electrified areas. They are prolific at Ashford (AC and DC), Dagenham Dock and Ebbsfleet (less sure about the last).

TI21s have an ASSC under 12kA fault current care of RLE (read CTRL which is now HS1 of course). However, I think some reading is required of earthing practices of AT and BT based electrification systems and some understanding of the EN standards.