Terminating Cable's of different CSA's, Whats the Regs Say?

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JuniorSparky

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hello Ive just joined, so hi everyone!

This forum has been helpful to me many times, reading your Q&As when I've needed help. But I couldn't find a question with this topic.

let's say we're installing a new Radial for socket outlets, all done in T&E. There's already an existing 6mm cable from the DB to the kitchen where the sockets are going. Would the Regs allow a higher CSA cable be joined to a smaller one, not fused down and the only protection at the DB by a 32A RCBO? For visualisation, let's say this is a 6mm being jointed to 4mm.

thanks for reading question, hopefully you'll be able to help. would be handy to page in the Reg numbers linked to this topic if you can, be much appreciated.

Cheers guys

 
You probably won't find a Reg  covering this .    Its a matter of common sense and in my humble opinion  is in the category of "  Working in the real world" 

The only thing wrong with your proposition is the rating of the circuit breaker  , which is a bit too high to cover the 4mm  unless its clipped direct .

It looks like you'd have to reduce to a 20A    or 25A  breaker  so may as well drop down to 2.5mm   radial .  

I think another option is the "Lollypop"   circuit  ,   where the 6mm  feeds a 2.5mm  ring  ( in the shape of a lollypop)    and back to a 32A  circuit breaker  . 

Welcome to the Forum by the way ,  glad you found it helpful before joining .     Don't forget theres a wealth of knowledge  in the archives  here ...I think you need at least Bronze membership to access  , not sure  but someone will.   

 
its fine, often done on longer runs for volt drop or where a cable goes through insulation etc and needs derated

have a look in appendix 15 too, shows a radial wired in 4 and 2.5 on a 32a (the 2.5 can only feed 1 point though)

 
Evans Electric said:
You probably won't find a Reg  covering this .    Its a matter of common sense and in my humble opinion  is in the category of "  Working in the real world" 

The only thing wrong with your proposition is the rating of the circuit breaker  , which is a bit too high to cover the 4mm  unless its clipped direct .

It looks like you'd have to reduce to a 20A    or 25A  breaker  so may as well drop down to 2.5mm   radial .  

I think another option is the "Lollypop"   circuit  ,   where the 6mm  feeds a 2.5mm  ring  ( in the shape of a lollypop)    and back to a 32A  circuit breaker  . 

Welcome to the Forum by the way ,  glad you found it helpful before joining .     Don't forget theres a wealth of knowledge  in the archives  here ...I think you need at least Bronze membership to access  , not sure  but someone will.   
Click to expand...
Definitely agree it is common sense & like you pretty much said, gotta think realistically what’s practical & acceptable in the real world. In reality I knew it would be completely fine, just remembered my tutor a few years ago mentioning fusing down cables of different CSA’s but I’ve over thinker it a bit. Cheers for answering and the samples aswell mate 👍🏻. & I’ll Hopefully get to bronze, always like to my brain storming on these types of topics 🗯️🧠

 
Andy™ said:
its fine, often done on longer runs for volt drop or where a cable goes through insulation etc and needs derated

have a look in appendix 15 too, shows a radial wired in 4 and 2.5 on a 32a (the 2.5 can only feed 1 point though)
Click to expand...
Now you mention it,  I do recall that illustration in the regs! Thanks for responding and the mentioning details mate ✊💫

 
Where CSA's changes and the new CSA is has a lower capacity then the protective device then you need additional overload protection...

BUT there is the proviso where CSA reduces AND there are no branches from the circuit....

that the additional protective device can be a bit further down the circuit NOT immediately at the point of change of CSA..

Have a read of 433.2.2

Guinness

 
JuniorSparky said:
hello Ive just joined, so hi everyone!

This forum has been helpful to me many times, 

Cheers guys
Click to expand...




Glad to hear that..

We do try and do our best..

Except the rowdies of course....

Deke

Binky

Kerching

Andy

Phil

Sidewinder

Pro Dave

OnOff

etc....

etc....

etc...

etc...

etc...

:D

:slap

:innocent

:coat

Sorry...

I may have had one-to-many celebrating Sidewinders "Grandad" news....

Guinness Guinness Guinness Guinness Guinness Guinness Guinness Guinness Guinness Guinness Guinness Guinness Guinness Guinness Guinness Guinness Guinness Guinness

 
Me?

Rowdy?

sorry you have the wrong person 

grumpy

arsey

intolerant of fools YES

but never rowdy!

well, there was this time once in B&Q  where I was not happy with their p. I. S. S. Poor customer service, reneging on warranties etc

that would have been classed as rowdy by onlookers...it was by the Manager and security staff  :innocent

 
SPECIAL LOCATION said:
Where CSA's changes and the new CSA is has a lower capacity then the protective device then you need additional overload protection...

BUT there is the proviso where CSA reduces AND there are no branches from the circuit....

that the additional protective device can be a bit further down the circuit NOT immediately at the point of change of CSA..

Have a read of 433.2.2

Guinness
Click to expand...
Quite so . .  The rule than allows single 1.5mm spurs off 2.5mm rings

 
Rowdy moi!  :pmsl1:

Congrats on becoming a grandfather @SPECIAL LOCATION   :kermit:

Getting back to the question, trying to run a spur in 4mm is probably a bad idea, simply because socket terminals have shrunk and getting 4mm in can be difficult. Also 4mm cable is expensive as it's low volume sales.

 

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