Cable size to alarm panel

RobTi · 4 Jun 2021

Hi already posted on the alarm section but thought better to post here as this is to do with power to the fused spur, my panel is connected by 2.5 t&e from the ring in the attic above it atm but I added a new socket into the cupboard just below the panel and wondered because of the load can I wire this in 1.5 t&e from the socket to fused spur ?
Thanks

JohnW2 · 4 Jun 2021

RobTi said:
Hi already posted on the alarm section but thought better to post here as this is to do with power to the fused spur, my panel is connected by 2.5 t&e from the ring in the attic above it atm but I added a new socket into the cupboard just below the panel and wondered because of the load can I wire this in 1.5 t&e from the socket to fused spur ?

Some clarification is needed. Is the current 2.5mm² feed a fused spur from the ring circuit?

Kind Regards, John

RobTi · 4 Jun 2021

Okay fitted a new socket in the cupboard back to back with the existing one which was on a ring but just spurred of this as there is no slack on the existing cables to continue the ring.
The existing power cable for the alarm is from the ring in the attic and was also just a spur off the ring.
The only reason I asked is the new socket is directly below the fused spur for the alarm so thought it would be neater to come of this socket 1m if cable rather than around 4 m of cable from attic

JohnW2 · 4 Jun 2021

RobTi said:
... The only reason I asked is the new socket is directly below the fused spur for the alarm so thought it would be neater to come of this socket 1m if cable rather than around 4 m of cable from attic

OK, thanks. Two more questions ... (1) what size fuse do you have in the FCU ('fused spur') for the alarm, and (2) what do you envisage using the new socket for?

Kind Regards, John

RobTi · 4 Jun 2021

JohnW2 said:
OK, thanks. Two more questions ... (1) what size fuse do you have in the FCU ('fused spur') for the alarm, and (2) what do you envisage using the new socket for?

Kind Regards, John

3a fuse and socket is used for a router and for a raspberry pi

JohnW2 · 4 Jun 2021

RobTi said:
3a fuse and socket is used for a router and for a raspberry pi

OK.

If I understand correctly, you have a ('unfused') spur from the ring in the attic feeding that FCU (with 3A fuse) which then supplies the alarm panel, and you have this additional socket (for router & raspberry pi), near to the FCU which you want to supply power to. Is that correct?

If so ... although it's a bit silly with the small loads you are talking about, the standard 'guidance' is that you should not supply more than one socket (or FCU etc.) from an unfused spur from a ring circuit, but you can supply as many things (sockets/whatever) as you like from a fused spur.

That being the case, the guidance would say that you should not connect your new socket to the 'supply side' of the FCU/'fused spur', but that you could connect it to the 'load side' (the side your alarm panel is connected to), hence also protected by that 3A fuse.

If 3A worth of supply (more than enough for what you've mentioned) is adequate for your needs, then that would be the simple way to go, and (to answer your original question) 1.5mm² cable would be fine for that. If you potentially wanted more than 3A to be available at the new socket things would get a little more complicated, so let us know.

Kind Regards, John

RobTi · 4 Jun 2021

Okay I have a what you would call a standard ring circuit in my attic that an electrician installed for me many years back, so I added a 2.5 cable into a socket and took this downstairs to a fused spur with a 3a fuse and this supplies the alarm panel. Now I have just added a socket into this cupboard by adding a third set of cables into the back of a bedroom socket as there was no slack to pull them through to extend the ring. So I was happy with this and then thought if it was possible to do away with the feed for the alarm fused spur and just take it from the back of the socket which I have just added
Thanks

JohnW2 · 4 Jun 2021

RobTi said:
Okay I have a what you would call a standard ring circuit in my attic that an electrician installed for me many years back, so I added a 2.5 cable into a socket and took this downstairs to a fused spur with a 3a fuse and this supplies the alarm panel. Now I have just added a socket into this cupboard by adding a third set of cables into the back of a bedroom socket as there was no slack to pull them through to extend the ring. So I was happy with this and then thought if it was possible to do away with the feed for the alarm fused spur and just take it from the back of the socket which I have just added

Oh, I see. I didn't realise that the new socket was 'already connected' to something.

What you currently have sounds fine. If you already have the feed from the attic to the 'fused spur' which is supplying the alarm panel, why are you thinking of getting rid of it?

Kind Regards, John

RobTi · 4 Jun 2021

JohnW2 said:
Oh, I see. I didn't realise that the new socket was 'already connected' to something.

What you currently have sounds fine. If you already have the feed from the attic to the 'fused spur' which is supplying the alarm panel, why are you thinking of getting rid of it?

Kind Regards, John

To tidy it up it’s around 4 m long and I just thought remove it and the put 1m of cable from socket up to alarm fuse and in my mind neater

JohnW2 · 4 Jun 2021

RobTi said:
To tidy it up it’s around 4 m long and I just thought remove it and the put 1m of cable from socket up to alarm fuse and in my mind neater

Fair enough, although I personally would probably not bother!

However, what I said before still applies - the only difference being that we are now talking 'the other way around'. If you want to comply with the guidance that one should not have two things (your 'fused spur' and the new socket) supplied by an unfused spur from a ring circuit, then you would have to take the supply (coming from a bedroom socket) first to the ('supply side' of the) 'fused spur', and then connect both the alarm panel and a cable to the new socket from the output ('load side') of the 'fused spur'.

Kind Regards, John

RobTi · 4 Jun 2021

Thanks I understand what you are saying bedroom to fused spur to new socket/ alarm panel so that they are both protected by the fuse. Will leave as is then as I said it was just a thought

JohnW2 · 4 Jun 2021

RobTi said:
Thanks I understand what you are saying bedroom to fused spur to new socket/ alarm panel so that they are both protected by the fuse. Will leave as is then as I said it was just a thought

Yes, that's what I meant - but, as I also said, I think that (like you now say) I would probably leave things as they are!

Kind Regards, John

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Cable size to alarm panel

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