radial from ring main

[Paul.M]

Worse case scenario, 2.5mm in three core enclosed in conduit in an insulated wall = 17.5a. So on a ring it would double to 35a and having a lower fuse to 32a to protect the cable. To spur off that ring without overloading a single section wild need investigation to the load on the ring before spurring off it. If your spurring off the first socket you will put the majority if the load on a single part of 2.5 on the ring and that's not good. (balanced ring).

 

[chiplard]

Can someone please tell me why Appendix 15 suggests a 4mm radial circuit should be protected by a 32A Breaker when the only installation method that this would suit is clipped direct.

Sorry to sidetrack the thread but i have always wandered.

 

[Guest123]

Seems a few people need to brush up on ring circuit theory.

 

[Paul.M]

Can someone please tell me why Appendix 15 suggests a 4mm radial circuit should be protected by a 32A Breaker when the only installation method that this would suit is clipped direct.

Sorry to sidetrack the thread but i have always wandered.

A 2.5mm ring = a csa if 5mm so any cable less than the ring can be protected by the same mcb. If it was a 2.5mm radial you can still increase the csa if the spur cable long as the main mcb is protecting the 2.5mm. Hence the reason for a fcu to protect the spurred cable and the flc for that spur.

 

[iconnect]

Ok my understanding don't shoot me !!! The idea of balancing a ring is crap the ring in its nature if installed correct is balance through each leg being as near as same length. If the first socket in that ring is used most of the current will go down the shortest leg and the rest the long way around correct!!! You can only spur once of a ring if no switched fused spur is used reason being you could connect 4x double socket on it and carry 32a on a 2.5 or 4mm but it would overload the shortest part of the ring it connects too. The reason we fuse it can not carry more than 13a due to the fuse therefore no different to pluging some thing in that pulls 13a!!! so the fact is 1x socket if spuring without fuse with fused spur as many as you want it will still only pull 13a. I hope that makes sense? You could do loads of stuff if you just look at one part of the regs it overlaps! The regs are for guidance they just prove or disprove you are breaking the law electricity at works !!

 

[nick611]

So, to all that have posted that it is fine to spur from a 32A, 2.5mm T&E ring final to any number of socket outlets without an FCU beforehand, can you tell me how it is we arrive at the scenario whereby it is fine to protect a cable with a CCC less than that of the associated OCPD, and the fundemental principals that allow us to do this???

lenny you.ve missunderstood.4mm cable has a ccc higher than the ocpd of a 2.5mm ring main.read the thread from the start,and calm down dear

 

[Guest123]

lenny you.ve missunderstood.4mm cable has a ccc higher than the ocpd of a 2.5mm ring main.read the thread from the start,and calm down dear

I have read the thread from the beginning thanks

My point is that you clearly dont understand the fundemental principals of a 2.5mm T&E ring final circuit protected by a 32A OCPD, and the effect 'spurring' off to multiple socket outlets without an FCU beforehand will have on that circuit, frankly that shocks me a little.

 

[nick611]

I have read the thread from the beginning thanks

My point is that you clearly dont understand the fundemental principals of a 2.5mm T&E ring final circuit protected by a 32A OCPD, and the effect 'spurring' off to multiple socket outlets without an FCU beforehand will have on that circuit, frankly that shocks me a little.

even if the spurs are from near to distboard a percentage of current will flow long way round. As 2.5 carrys 80 plus percent of total possible load {32a} i dont think your objections are as well founded as you think they are

 

[chiplard]

hi there, would like your views on this.. Jb off a ring main and run two or three socket,s on a 4mm radial. I myself don,t mind it. no current capacity issues.and no zs problem,s if rcd protected.Any thoughts.

You asked for peoples thoughts, you got them!!!

Seems to me you will do what you want to do anyway, so carry on.

 

[kmcgold]

nick611 has anyone else agreed with you
that you can run 2 or 3 sockets of in a 4mm radial ?

 

[Sav]

Hi everyone,
how about this one then.

outside socket is currently part of a small 2 bed flat ring.

the outside socket has been discarded and an adaptable box has been placed there. From there 4mm swa approx 6 metres into a small summer house feeding 4 sockets and 2 4ft flourescents.

the 4mm swa is made of into a small c/unit and all wiring is in plastic conduit. the small c/unit has a 63a double pole isolator ( no rcd protection as the flat ring that the swa is spured off from is protected by rcd already.

I am carrying out an inspection on this, so would you say this is ok, or not to regs etc.

Thanks for ready and any advise etc would be helpful,
Sav

 

[kmcgold]

i would say no

 

[Sintra]

even if the spurs are from near to distboard a percentage of current will flow long way round. As 2.5 carrys 80 plus percent of total possible load {32a} i dont think your objections are as well founded as you think they are

Have you actually read 433.1.5 and thought about the path of least resistance?

 

[iconnect]

No thats not ok !!! Only if you take the adaptable box out and put a switched fused spur IP Rated with a 13a fuse in. The main switch is not rated to the 4mm and it could carry more than 13a !!!!

 

[Sav]

No thats not ok !!! Only if you take the adaptable box out and put a switched fused spur IP Rated with a 13a fuse in. The main switch is not rated to the 4mm and it could carry more than 13a !!!!

Why not leave the adaptable box where it is !!!!!!! Its big enough to fit a 13a SFCU inside it and its IP65 rated !!!! . Also why the !!!!!, i only asked thats all,
Thanks
Sav