In what ways can an EMU fail in service?

North London Line screwed up at lunchtime due to an earlier failed unit at Finchley Road & Frognal. What can go wrong with an EMU?

It stops working!Think how many components are on a modern unit and then imagine how they can fail to function, add to that software glitches, plus numerous other possible problems.

I'd suggest possibly traction motor damage/burnout?? Just as a guess for starters.

Anything and everything.

Brake continuity lost, MCB tripping out, door faults, air burst, compressor fault, traction fault, dragging brake, converter fault, radio failure, broken wiper, horn failure, any safety system failure, stuck relay, broken drivers seat, cracked windscreen, headlight failure, passcom won't reset, fire detection fault, PA failure etc etc etc.

bionic said:

Anything and everything.

Brake continuity lost, MCB tripping out, door faults, air burst, compressor fault, traction fault, dragging brake, converter fault, radio failure, broken wiper, horn failure, any safety system failure, stuck relay, broken drivers seat, cracked windscreen, headlight failure, passcom won't reset, fire detection fault, PA failure etc etc etc.

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In short: mechanical or electrical failure!

Obviously they are more reliable than DMUs due to the reduction in mechanical components. But as above, there are countless things that can go wrong. What the TMS (train management system) computers of a modern unit usually provide are a means to quickly diagnose faults and help to get the train out of the way, or back into service when possible.

tom73 said:

North London Line screwed up at lunchtime due to an earlier failed unit at Finchley Road & Frognal. What can go wrong with an EMU?

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Some of the most debilitating failures can be due to wiring faults, or water ingress affecting wiring or relays. This is particularly poignant during very cold weather, which is often the straw which breaks the camel's back of any pre-existing defect which hasn't yet reared its head. Likewise freeze-thaw action can cause air leaks in pipes and hoses, and especially at the joints and points of connection.

Most electrical and pneumatic circuits are arranged in such a way that most individual pieces of equipment can be isolated (albeit instructions may then require the train to be withdrawn from service or driven at a reduced speed if it's safety equipment). Things which can't be isolated may be duplicated instead. Something like a braking circuit may well have well into double figures pieces of equipment on it. Things like wiring faults (e.g. open circuit due to water ingress or wire damage) will test the staff's defect-handling ability as it will often cause things to behave in ways not taught during training -- and will separate those staff who actually understand the train from those staff who have just learned the flowcharts.

If all else fails, there's various fall-back options. One is to try driving the train from the other end (relying on the fact that many circuits or parts of circuits are duplicated), or failing that to use an assisting train. The worst-case scenario is if the brakes can't be released for whatever reason, as it's not possible to push a train with brakes hard on. So the ultimate "get moving" option is to isolate the brakes on the entire defective train and simply move it as an unbraked unpowered mass - but one has to consider what might happen if the coupling failed, and how the train would be stopped in that situation. One option is to leave handbrakes on, another is to find a way of boxing in the unbraked vehicles.

Generally one has to be unlucky to get two defects at once, which again can test staff response. Unfortunately most double defects tend to happen as a result of someone messing something up when responding to the initial defect - my mind takes me back to something a couple of years ago when we had a train with all its shoes knocked off, and then a second problem was created when a heavy-handed member of staff broke a receptacle box when yanking the leads out (not in itself a problem as there are other boxes, but the train detected the associated switch as being in the wrong place which promptly locked the brakes on - again not an immediate problem as this circuit could be isolated, but isolating the circuit then prevented the train being driven in reverse which we needed to do for various reasons!).

tom73 said:

North London Line screwed up at lunchtime due to an earlier failed unit at Finchley Road & Frognal. What can go wrong with an EMU?

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Anything you can think of! The list will be pages and pages and pages of possibilities

Do not underestimate the complexity of modern trains. An EMU is not just a motor with a variable resistor to control it!

pdeaves said:

Do not underestimate the complexity of modern trains. An EMU is not just a motor with a variable resistor to control it!

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indeed. On board computer firmware bugs is the next pet hate for sure.

having the latest and greatest is not always the best plan.Having a stable system is more important.
Engineers and developers do cock things up from time to time,as no doubt many of you will have experienced from PC/Android/IoS software on your computers and phones!

tom73 said:

North London Line screwed up at lunchtime due to an earlier failed unit at Finchley Road & Frognal. What can go wrong with an EMU?

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Twitter suggests it wasn't even an EMU that failed, but a freight train obstructing the route.

samuelmorris said:

Twitter suggests it wasn't even an EMU that failed, but a freight train obstructing the route.

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It was a failed freight.