NEWBIE - Help please extending 4 core ext armoured cable.

[Simon35]

Does it still trip if the old cable is connected into terminals at the mid-way JB, nothing connecting those terminals together and nothing is connected in the other side of the terminals?

Yes is does.

To start with I wired the 2 earths (cables 3 and 4) into the same terminal, then tried with each in a separate terminal and then leaving cable 4 un terminated as it used to be terminated to an earth post in the old socket and there isn't a corresponding earth post in the new junction box.

All 3 variations tripped the breaker.

How is the armouring on the existing cable now connected to earth at each end? Does the armoured cable go all the way to the garage consumer unit, and if so how is the armouring earthed there? How was it connected to earth? Is the new JB plastic or metal? Was the old socket plastic or metal?

You need to access the other end of the cable, so that you, or an electrician, can test the cable and confirm it is installed and terminated correctly, at each end.

 

[adie68]

Does it still trip if the old cable is connected into terminals at the mid-way JB, nothing connecting those terminals together and nothing is connected in the other side of the terminals?

Yes is does.

To start with I wired the 2 earths (cables 3 and 4) into the same terminal, then tried with each in a separate terminal and then leaving cable 4 un terminated as it used to be terminated to an earth post in the old socket and there isn't a corresponding earth post in the new junction box.

All 3 variations tripped the breaker.

How is the armouring on the existing cable now connected to earth at each end? Does the armoured cable go all the way to the garage consumer unit, and if so how is the armouring earthed there? How was it connected to earth? Is the new JB plastic or metal? Was the old socket plastic or metal?

You need to access the other end of the cable, so that you, or an electrician, can test the cable and confirm it is installed and terminated correctly, at each end.

I think it might be time to call a professional.. this is all getting beyond my limited knowledge I think.

As far as I can tell the original cable is not armoured. It is probably 12 or 15 years old. It certainly doesn't have a steel wire sheath but layers and layers of very tough plastics.

The old socket was plastic the new JB is also plastic.

Going to have to leave this to the weekend now as it seems I have no choice but to rip down a wall to get full access to the CU in the garage.