New socket from spur

[JohnNox]

TBH i'm not sure if it's really a spur or a radial circuit itself, since the cable begins on the MCB?

Out of curiosity, what do the regs say about multiple rings beginning on a single MCB - are those multiple circuits or one?

What about a ring and a radial on one MCB? Get's tricky!

In any case, I did the small modification connecting a single socket on the supply side of the existing FCU of the "spur" as ELFImpudence suggested, all good.

 

[EFLImpudence]

Do you just make up your own regs then ?

If that is intended for me then the answer is no, but we are allowed to think and design circuits so they are safe.

Please feel free to state specifically what you think is wrong with my advice.

 

[Blueflash]

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

Dave

 

[EFLImpudence]

TBH i'm not sure if it's really a spur or a radial circuit itself, since the cable begins on the MCB?

It's called a spur but as you can see it is no different than a radial.

Out of curiosity, what do the regs say about multiple rings beginning on a single MCB - are those multiple circuits or one?

It is classed as one circuit. The definition of a circuit is equipment and cables protected by the same OPD (fuse/MCB).

What about a ring and a radial on one MCB? Get's tricky!

Nope, no different.

In any case, I did the small modification connecting a single socket on the supply side of the existing FCU of the "spur" as ELFImpudence suggested, all good.

Ok, so now you have a 2.5mm² radial (part) circuit, albeit from a 32A MCB, with one socket on it (where a double is allowed) for your thermostat - to which you have added an alarm which are both protected by 3A fuses

 

[john4703]

The Nest thermostat should be on the same circuit as the boiler and heating.

It should be connected near the boiler or wiring centre.

Why? It is often better to have the thermostat in an area that is heated even if the boiler is in a utility room that is unheated. Is there and reason to run extra mains cables to feed the Nest thermostat to have it on the same circuit as the boiler?

 

[EFLImpudence]

No, we have solved that. I initially thought the OP was referring to the receiver.

 

[winston1]

What about a ring and a radial on one MCB? Get's tricky!

The "radial" is a spur that happens to connect at the MCB rather than part way round the ring. The same rules apply one single or one double socket or one FCU.

In any case, I did the small modification connecting a single socket on the supply side of the existing FCU of the "spur" as ELFImpudence suggested, all good.

In which case what you have done is non compliant.

 

[JohnNox]

In which case what you have done is non compliant.

So I have a (20cm long) spur that has a single socket AND a 3A FCU. I don't believe it's non-compliant as it can't overload the cable. Professionals seems to be split on this issue (both here and in other forums I have searched online). I'd appreciate a segment from the regs that specifically says this is non-compliant (and an explanation as to why).

 

[winston1]

So I have a (20cm long) spur that has a single socket AND a 3A FCU. I don't believe it's non-compliant as it can't overload the cable. Professionals seems to be split on this issue (both here and in other forums I have searched online). I'd appreciate a segment from the regs that specifically says this is non-compliant (and an explanation as to why).

I don't make the regs but you are only allowed one single or double socket or one FCU on a spur however short it is. Suggest you search the regs yourself. Suppose you put a 13 amp fuse in your FCU and a 13 amp fuse in the plug?

To make it compliant just run another 20cm long spur from the CU.

 

[EFLImpudence]

It is not what an "informative Appendix picture" shows and states.

Look at it another way, John.

Had you swapped the FCU for a double socket and plugged in the alarm and thermostat, no one would be complaining but see if you can find a difference, safety wise.

Another way would have been to change the cable from CU to FCU to 4mm² that would not contravene any regulations but people would still say "It's not in the picture so it can't be right".
Had you changed all the cable from CU to new socket to 4mm² you would also be allowed to extend this cable and add as many socets as you like. Would that still be a spur?

 

[EFLImpudence]

Suppose you put a 13 amp fuse in your FCU and a 13 amp fuse in the plug?

Wouldn't that be the same as a double socket?

 

[Yorkshirebloke]

Is a rfc and a radial on one MCB not classed as a single circuit? If so, surely it's fine?

 

[EFLImpudence]

Yes, I don't think anyone is arguing about that part of it.


RFC stands for Radial Final Circuit as well.

 

[Yorkshirebloke]

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?

 

[winston1]

Wouldn't that be the same as a double socket?

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