FCU to step down amp rating

[jonsho]

Hi all,

Question around using multiple FCUs in a circuit.

I've drawn some pictures to illustrate what I currently have and what I'd like to do, all dependent on whether it's safe/allowed!

Currently I have a direct line from the CU to a small 3a fcu that feeds the alarm backup module.

I want to put a small fridge in this cupboard and this line out is the easiest to access.

Can I add a further FCU, at 13a with a double socket spurred off by tapping in to this line. Then continue the wiring from the 13a FCU (load side) to the 3a FCU that then feeds the alarm module.

The pictures may help explain better.

Thanks in advance.

 

[EFLImpudence]

Yes, that's fine.

What is the rating of the circuit device in the consumer unit?

 

[jonsho]

Thanks for the response, not sure if this answers your question, but this is the circuit it would be pulled from:

 

[EFLImpudence]

Ok. I thought from what you said it was separate circuit.

 

[SUNRAY]

What do you mean by :

Currently I have a direct line from the CU

That MCB is marked as ground floor sockets and

alarm

It would be easy to assume you have a whole ring or radial circuit on that MCB of which just one point is your

small 3a fcu that feeds the alarm backup module.

something like this:

IF that is the case then adding a double socket would not require a FCU, either by adding:
Spur from existing FCU live side:

Or adding it into the ring (Or radial as appropriate):

However first you will need to ascertain exactly what you currently have.

 

[jonsho]

Thanks for the reply.

I've opened it up to check.

Ring goes off from bottom of box to sockets. T&e Wire out, wire in.
Alarm circuit comes off as a single radial circuit wired in to the same mcb as a standalone.

Again, I've tried to draw to illustrate... bear with me

 

[terryplumb]

Your original proposal , introducing a FCU with 13 amp fuse is ok ,but you should connect the new socket and the alarm FCU to its load terminals.

 

[SUNRAY]

No bearing wth required, so far you have provided excellent sketches.

Next we need to workout what size the spur cable is

If you are unsure, approximate dimensions can be found here: https://www.diynot.com/diy/threads/duplicate-electrics-now-in-wiki.224859/#post-201507

 

[jonsho]

Thankfully it looks to be run in 2.5mm T.E, I've got a spool in the shed so can keep it all the same gauge!

 

[SUNRAY]

Thankfully it looks to be run in 2.5mm T.E, I've got a spool in the shed so can keep it all the same gauge!

One option and probably the easiest, although frowned upon for reliability of the alarm system would be to replace the FCU with a double socket and plug the alarm into it:

As Terry has already mentioned, this is arrangement is correct:

 

[SUNRAY]

Of course another option would be to fit an additional MCB (16A) in the CU rather than a 13A FCU, however that would be creating a circuit and require the raising of paperwork.