BR did experiments with this when they were investigating 25kv electrification back in the 50s. They found with a really sooty filthy exhaust from a 9F, the OHW could get within 3 inches of the chimney before it flashed over. They also contemplated dropping the voltage to 6.25kv in tight clearance areas, but decided after trials and clearance easement it wasn't necessary.

Tony G

On 14 May 2016, at 8:44 pm, Matthew Geiermatthew@... [TramsDownUnder] TramsDownUnder@...> wrote:

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> On 14/05/16 13:02, Tony Gallowayarg@... [TramsDownUnder] wrote:

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>> Presumably the track and structure/loading gauge are the same as the rest of the system - sounds like some jobsworth reciting “computer says no” while making no effort to get any other result :

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>> http://www.theguardian.com/uk-news/2016/may/13/borders-trip-off-as-flying-scotsmans-wings-clipped-by-network-rail

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>> Just like here.

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> There might be something in it though - a number of years ago, I was some what amazed at how low the 25kv overhead was in Edinburgh Waverly station, and how close the wire was to the steel pedestrian bridge structures. They had insulating panels between the wire and the bridge, panels wide enough to ensure the pantograph's didn't earth to the bridge. And the pantograph on the trains looked almost stowed as the trains passed.

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> Between the low overhead and the proximity to bridge structures, some one's had a panic and the possibility that if the kettle is sent into the 'wrong' platform at Waverley, the steam and soot will cause the overhead to flash over.

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