radial circuit

[20al]

i have installed a 4mm radial circuit protected by 32a mcb feeding 5 twin skts, customer now wants 1 more skt but have run out of 4mm cable. If i run last leg in2.5 cable will i be complying with current regs ?

 

[Deleted member 26818]

Yes you will be.
It will be classed as a spur, so only one double socket can be used unless you use an FCU.
No different really to spurring off of a RFC.
Have a look in Appendix 15 of BS7671 if you want to check.

 

[i=p/u]

well 2.5 only goes to about 28A (tabulated) and you have 32 amp breaker

 

[20al]

well 2.5 only goes to about 28A (tabulated) and you have 32 amp breaker

take your point, but if your allowed to spur off a 2.5 ring isnt this the same ?

 

[j.mawer]

But as you can only plug in 2 13A fuses so draw 26A...

 

[i=p/u]

what if all other sockets are on load too, would it burn over time

 

[j.mawer]

If it were a spur (or the last socket which is the same thing) then the current wouldn't be going down the 2.5mm

 

[Deleted member 26818]

Why would loads in front of the smaller CSA cable cause it to burn?

 

[Phil]

reg 433.1 "an unfused spur run in 2.5mm cable should feed one single or one double twin socket - outlet only"
so yes is the answer

 

[i=p/u]

ok yous win, i surrender

 

[20al]

thanks all,just glad to hear i havent got to buy another drum of 4mm

 

[i=p/u]

i just thought In had to be equal or greater than ib and It had to be equal In. if you get me

 

[nickblake]

i just thought In had to be equal or greater than ib and It had to be equal In. if you get me

?Yes mate but as has been mentioned its in appendix 15 and as Phil has said there is not a problem as long as its only a single or twin socket outlet , stick an FCU on it and the last leg could be wired in 1.5mm twe

 

[j.mawer]

I get you. But if the design current will be 26A 2x13. The tabulated value is 28A
Now if the load of either socket goes above 13A then its fuse will blow in the plug, disconnecting the load, so you could argue that the cable is protected by a 26A fuse so (In = Ib) < It.

And its in the regs as mentioned!

 

[Geoffsd]

The circuit protection device doesn't have to be at the beginning of a circuit. It can be at the end, i.e. the fuse(s) in the plug(s).

So the cable cannot be overloaded. That's why only one is allowed without an FCU.

One socket, that is.