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Originally Posted by BBKing
If it's that easy to break by hand presumably it would be broken in the event of a derailment? In the Severn Tunnel instance you'd want it to break if the other line was fouled, as the axle counters, even if they were working, wouldn't detect a fouling, and of course it's dark (of course you've got the poor guard slogging up the line with some detonators, which can't be fun in a wet four mile tunnel).
Can't remember off the top of my head whether the wire in 1990 was broken by hand or by contact with the trains - since it was a fairly low speed shunt I suspect by hand though, but IIRC the opposite line wasn't fouled.
Edit - teach me not to check, the crash was on December 7th, 1991.
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Definitely by should be broken by hand, as they (there are two - one each side) are on the tunnel walls.
With the reliability of the axle counters, they may as well have stuck with track circuits. I supose the only advantage is that the engineers don't have to walk through a cold, dark, wet tunnel to fix it.