Thread by @NetworkRailSE

⚠️🚦 Sorry to say we have a signalling problem in one of the worst places it could be - right outside #Lewisham station. We've got a team on site investigating the issue but it means disruption to @Se_Railway services this evening and we advise people check before they travel. /1

@Se_Railway A detection circuit that tells us where trains are has failed on the scissors crossover in the picture, putting all signals on the approach to red (as you can see in this @traksyuk graphic). We are having to talk each train past those red signals manually. /2

@Se_Railway @traksyuk That takes time and would cause major problems if we tried to run a normal evening service, so many trains have been diverted away from #Lewisham itself until we can fix this. If you follow @Se_Railway they will have those details. /3

@Se_Railway @traksyuk This is the problem here - circuit LC - which control the crossover and the signals on the approach. It uses electricity at audio frequencies played through those green tracks to detect trains - if a train short circuits the tracks, the signals go red. /4

... but other things can cause a short circuit, like a broken rail joint, which will also cause the signals to go red and we have a problem. We know #Lewisham is a cause of continuing dismay to commuters and we are upgrading the area's track and signals. /5

... with a major investment coming this Christmas, and a great deal of work already under our belts.
There's more details here:
networkrail.co.uk/running-the-ra….

We're really sorry for the disruption this evening and our team on site is doing everything they can to find the cause of the problem and get this fixed ASAP. Ends.

UPDATE on #Lewisham: a piece of metal had blown across an insulated joint and short circuited the train detection equipment. We've removed it and all is well again. We will gradually reintroduce services from now on this evening. Thank you for your patience tonight.

Correction: Although the track was short-circuited by a flake of metal, it is unlikely to have blown there, but most likely picked up by a train wheel miles away and then through bad luck, deposited itself across the joint. Again, apologies for the disruption.