New socket from spur

[JohnW2]

So if it's a radial circuit, there is no limit to how many sockets you can have on it right?

That depends upon the cable size and the rating of the MCB/fuse. If it's 2.5mm² cable with an 'appropriate' MCB (20A, possibly 25A), then you could have as many sockets as you wanted (a 'real radial'). However, if it were 2.5mm² cable protected by a 32A MCB (as it probably would be if it was sharing an MCB with a ring circuit), you would be limited to one (single or double) socket.

Kind Regards, John

 

[winston1]

Aye, I'm just also trying to get my head round it

So if it's a radial circuit, there is no limit to how many sockets you can have on it right? (Although I did read that floor area was a limiting factor, although I'd also read that wasn't actually set in stone)
Is it the fact it's a fcu that's the problem?

No. A radial circuit on a 20a MCB in 2.5mm cable or a 32a MCB with 4mm cable can both have unlimited sockets. But not a radial in 2.5mm cable on a 32a MCB which is the case with a spur on a ring final.

John2 beat me to it.

 

[Yorkshirebloke]

Ah, I see, so it's the fact the MCB isn't protecting the cable that's the problem, not that there is an fcu somewhere in the line.

 

[sparkwright]

The question is - is a fused connection unit the same as a single socket?

The major difference is that a fused connection unit will have a fixed load connected to it, and single socket could have god knows what plugged into it.

That said, if an adapter is used in the socket for multiple appliances, the adapter (at least the modern ones) will have a 13amp fuse in it.

If a 32amp ring has a so-called radial with two or more accessories spurred off it at the origin, then this could be a radial wired in 2.5mm2 protected by a 32amp protective device, which is not considered good, and not a recognised circuit arrangement.

Technically, it may well be permissible to spur from a ring in 2.5mm2 cable and feed 4 FCUs fused at 3amp. Or even 8 FCUs fused at 3amp. Then again, even more than that if the load of each FCU is actually a lot less than that of the fuse in the FCU.

It was allowed once for a spur from a ring to serve two single sockets, but not now.

Which takes us back to the question - is a FCU the same as a single socket?

It also takes us back to the possible need for an accessory to be designed which comprises of one single socket and one FCU. This would need one set of terminals to supply the socket outlet and the supply side of the FCU, and another set of terminals for the load side of the FCU.

 

[EFLImpudence]

So if it's a radial circuit, there is no limit to how many sockets you can have on it right?

Right as long as the CCC of the cable is more than the OPD rating.

(Although I did read that floor area was a limiting factor, although I'd also read that wasn't actually set in stone)

That is correct - but what relevance has the floor area?
Sometimes I wonder about the authors of such "rules".

Is it the fact it's a fcu that's the problem?

Not really.
It is just because Appendix 15 - only informative - says you can only have one socket on such a spur - but it can be a single or double.
(You can have as many sockets as you like on the load side of an FCU but obviously the current is limited to 13A.)

If john had connected his new socket to the load side of the FCU no one would have complained, but a fault would disable both his alarm and thermostat.

 

[EFLImpudence]

No. Many double sockets are rated at 20a (not 26a).

So - an FCU and single socket with 13A fuses would be LESS hazardous.

I presume you mean 13A appliances rather than just fuses.
I wonder if the OP has two 13A appliances.

I believe you know that the fuses are to protect the cable; not the appliances.
Would that be the case in this example? Clue: yes it would.

 

[EFLImpudence]

Ah, I see, so it's the fact the MCB isn't protecting the cable that's the problem, not that there is an fcu somewhere in the line.

The cable is being protected against overload by the fuses.
It will also be protected against fault current by the MCB.

The only problem is a lack of a picture showing your arrangement.

 

[ban-all-sheds]

No. A radial circuit on a 20a MCB in 2.5mm cable or a 32a MCB with 4mm cable can both have unlimited sockets. But not a radial in 2.5mm cable on a 32a MCB which is the case with a spur on a ring final.

A 2.5mm² 32A radial with 2 single sockets would have (subject, of course, to installation method) Ib ≤ Iz, downstream overload protection and adequate fault protection.

You can't disallow something which is OK on the basis that at a later date someone might change it to be not OK. You wouldn't disallow the 20A radial because someone might come along and change the MCB to a 32A, would you.

 

[ban-all-sheds]

I don't require your permission to post on this site ......

Dave

I don't think EFLI was saying that you do.

But if you think that you are not required to answer questions which arise from your posts then this site is not for you.

 

[securespark]

Do you just make up your own regs then ?

No. He's just saying the situation is not dire as you seem to be implying.

 

[ban-all-sheds]

I really can't work out who "he" and "you" are in that...

 

[securespark]

"He": the person that comment was aimed at.
"You": the person commenting.

 

[ban-all-sheds]

I may go back to bed and start again.

 

[EFLImpudence]

"He": Me.
"You": Someone else.

 

[securespark]

I may go back to bed and start again.

We all get days like that.