Quote:
Originally Posted by Deathbyteacup
I think in the case of some classes, they have two pantographs as a requirement to run through the Eurotunnel, infact they have an entire redundant electrical system, to prevent a train becoming stranded in the tunnel and disrupting the service.
Certainly this is the case for Class 92. I imagine similar reasons exist for other classes.
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I think you're probably right about this. Nowadays most pantograph fitted stock is protected by an ADD (Automatic Dropping Device). It usually consists of a small air pipe which pushes the carbons (at the top of the pan) against the OHLE contact wire. If there are any problems with the way the pan is riding, or if the carbons become damaged it will bring the pan back down. Once this happens the traincrew aren't allow to try to raise it again until a Fitter has checked it. So when you're in a tunnel under the sea where it would take a considerable time to get a fitter to you, it would make sense to have a spare one.
Different classes of traction may have different reasons of course for having two pantographs, but nowadays it's considered a good thing to minimse the number of pans in the air when travelling at speed, as this can cause resonance on the OHLE.