Timer Tripping (or not)!

[Glyn1959]

Hi, I have the following set up that trips immediately I turn the switched FCU on. Can anyone explain why?
I had a radial circuit to bathroom (built in former garage space) to switched FCU (with 13A fuse) to electric towel radiator and all works perfectly.
I wanted to add an electronic timer between the FCU and the radiator.
A few years ago a spark tried to fit one for me but it kept tripping (even after exchanging the timer thinking it was faulty) so he gave up and fitted a blank on the box.
Recently I decided to have another go. Unfortunately the spark had cut the cables to minimum to fit them in connectors behind the blanking plate. So, firstly I extended both cables with spare lengths of 2.5mm cable (via the connectors) and wired to the new timer. The timer came on and went off as planned - Happy days
I cut the “test” cables to fit in a deeper pattress and reconnected to the timer and fitted to the new pattress.
Now, immediately I switch the FCU on it trips at the board!
Confused? I am!

 

[ban-all-sheds]

Hi, I have the following set up that trips immediately I turn the switched FCU on. Can anyone explain why?

What trips? An MCB or RCD?

I wanted to add an electronic timer between the FCU and the radiator.

Why not just replace the FCU with a timed one?

Now, immediately I switch the FCU on it trips at the board!
Confused? I am!

If it works when not fitted into the back box and causes a trip when it is then there's probably a trapped wire somewhere creating an earth fault.

 

[Glyn1959]

What trips? An MCB or RCD? = RCD

Why not just replace the FCU with a timed one?
= I already have two sunken boxes so I will still have two boxes either way (FCU inc timer + blank or FCU + Timer)

If it works when not fitted into the back box and causes a trip when it is then there's probably a trapped wire somewhere creating an earth fault. = Have checked for this but will check again

Thanks

 

[ban-all-sheds]

 

[ban-all-sheds]

I already have two sunken boxes so I will still have two boxes either way (FCU inc timer + blank or FCU + Timer)

Well, you do now (although could you not get rid of one?)

But at the time, why have a new hole in the wall and 2 accessories rather than just put a timed FCU in?