Upon last night's bucked loads of rain falling, I've noticed an extremely loud cracking noise seemingly coming from the conductor rail. The acceleration is also jittery. Is this a new thing in wet weather or something to do with the condition of the conductor rail or normal? Haven't heard it as badly as lately. Clearly sounds like constant arcing.
It's just water interfering with the contact between the conductor rails and the pick-up.
It can be quite spectacular in conditions of freezing fog. (Where the water is in the form of ice crystals on the rail.
ETA: I should add that the reason that the crackling is louder when the rails are wet is down to the electrolysis of the water that is impeding pick-up.
When you pass a current through water it electrolyses it into hydrogen and oxygen (+heat), and, given that there is arcing involved, this is immediately recombined in a mini-explosion. Hence the extra crackling.
ETA -> Edited To Add.
Also, I've just noticed that I said 'louder' here, and then contradicted myself in a later post.
What I meant in this post by 'louder' is that there's more of it. So the instances of noise are more frequent, rather than the level being higher.
Arcing is common place on 3rd / 4th rail open contact railways in damp/wet/frosty conditions. The 1996 stock aren't smoothest pulling away under dry conditions but in the wet, wheel slide protection cutting out the motors once slippage is detected means that trailers and motor cars jostle with each other as the momentum of the aggressive acceleration rate of ATO subsides temporarily.
Below is a an example of arcing from a 1996 stock leaving Finchley Road on the Northbound. Damp conditions, a rail section gap and point work all contributors here.
There are rarely problems with rainwater as it’s a conductor of electricity, as has been said hail, ice and snow are not.
It is a conductor to a degree*, because it is generally very weak nitric acid, but it will still electrolyse, and the resultant hydrogen and oxygen can recombine in tiny explosions.
If you listen carefully to the (electrical) sound made by a train on wet track, it is softer than that made by normal arcing, because the electrolysed hydrogen and oxygen are not contained meaning they ignite with more of a 'flt' or a 'whump' than a 'bang' or crack.
* If it was a good conductor we would have all sorts of problems all over the place. Track circuits would all fail to operate correctly in the rain, for example.
Indeed - I learned on this very forum a few years ago that actually, water is a very poor conductor.
I always struggled with how Network Rail get away with steel rail sleepers worked until I found this out...
Also explains how we get away with carrying water fire extinguishers on our trains. IIRC the water in them is deionised as deionised water is an extremely poor conductor.
This is true, but it's worth pointing out that it's dangerous to extrapolate too far from this.
You can't assume that water and electricity are safe because even a very small amount of salt (and this is any salt, not just NaCl) will make the water a conductor, and only a very small current flow can be enough to kill.