Cheers for the input securespark.
It was most probably just a shower upgrade by the home owner who knew no better.
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Well whilst I was hoping this was the case, I'm starting to think otherwise. I've had a look in the CU this afternoon, to see if extending the neutral cabling is necesarry, or if with a little thought and time whether it can be run a different way, avoiding using a terminal block.
Fortunately next to the consumer unit there's some trunking, that runs along the top into a junction box and then another piece running out the top and up into the ceiling.
I've took the cover off the trunking and saying it's cramped would be an understatement. I've took the cover of this junction box ( which is nothing more than a twin gang patress with a blank on the front) and it's "chocker" full of chock block (sorry, couldn't resist). I wished I'd left the lid on.... Non of them are taped up (personally like to see them taped) and even worse there's bare copper exposed on everyone. It's just a short waiting to happen....
Anyway fortunately my shower cable is joined in this junction box. Not sure why the installer didn't take the time to make a proper job of it in the first place. But with a little bit of new trunking and it's own junction box it'll be more than long enough to reach the MCB, earth and neutral rails.
Well I thought I'd give everything a check tighten before popping the cover back on and found a few loose connections on the earth and neutral rails.
I'd seen a topic on here yesterday regarding RCD Test button issues. With this in mind I thought mines got to be due a test. And you guessed it, it failed to trip (this is with the main isolator now and a few circuits)......
Whilst I feel comfortable doing the shower job I'm starting to seriously doubt all the electrics, so think it might be worth calling a spark in and getting a PIR carried out.
Cheers