Sorting out a mess... Ring on the end of a radial?

[dhutch]

Hi,

Can you legitimately have a ring final on the end of a radial? Effectively bring the two last cable runs back to the consumer unit together into a single larger cable.

Ive got a bit of a mess to sort out with the wiring of my house, originally rewired wired in the 80's most of the house is sound if basic but it has been hacked about a bit, and while Im not planning to invest in rewiring it all, im intending to correct or have corrected the additions to a suitable standard.

Currently in addition to the main ring main there is a 6mm radial which runs in the ceiling space to the otherside of the house where it terminates in a large round junction box in the ceiling space, which I have found and made an access hole to. From that there are five runs of 2.5 twin and earth, one goes to a double socket, one goes to a fcu which feeds the boiler, one feeds the downstairs loo light, and the final two run on, via a pair of junction boxes (presumably cut the cable too short) , to three double sockets in a ring around the conservatory which contains the washing machine and drier.

It would not be a hard job to move the loo light to onto the downstairs lighting circuit. But obviously to extend the ring back to the consumer unit would be a right pain, as would rewiring the conservatory as continuation of the radial because its all plastered in.

Therefore my best thought is to crimp on an extension to the 6mm radial and run it down by the side of the boiler, where I can have an accessable junction to start the ring, which can be made to include the FCU and the socket.

I cant see it being unsafe, but is that allowable?


Daniel

 

[chivers67]

What fuse is the 6mm terminated in the Consumer unit?

 

[Chri5]

It is safe, and was once used quite a lot. Like a central main back bone.

Thing being that now we have separate fuses for separate services to avoid a Big Bang moment and also to isolate sections of the home power.

I'd think about re wiring the lot or at least split the circuits up a bit.

 

[EFLImpudence]

Can you legitimately have a ring final on the end of a radial? Effectively bring the two last cable runs back to the consumer unit together into a single larger cable.

A lollipop.
There is nothing electrically against this as long as all the cable ratings comply.

Currently in addition to the main ring main there is a 6mm radial which runs in the ceiling space to the otherside of the house where it terminates in a large round junction box in the ceiling space, which I have found and made an access hole to. From that there are five runs of 2.5 twin and earth, one goes to a double socket, one goes to a fcu which feeds the boiler, one feeds the downstairs loo light,

and the final two run on, via a pair of junction boxes (presumably cut the cable too short) , to three double sockets in a ring around the conservatory which contains the washing machine and drier.

It would seem quite acceptable (old shower circuit?).

You could argue, dependent on all required conditions being met, that it could even be on a 32A opd - more than the 2.5mm² cable could handle as it (the 2.5mm² cable) cannot be overloaded.

It just seems, from here, a mess but if everything complies then what is wrong with it?

I cant see it being unsafe, but is that allowable?

I tend to agree so why not?
I would leave a lot of paperwork explaining everything.

 

[JohnW2]

Can you legitimately have a ring final on the end of a radial? Effectively bring the two last cable runs back to the consumer unit together into a single larger cable.

A lollipop. There is nothing electrically against this as long as all the cable ratings comply.

Indeed - and it might even make sense in some situations - e.g. if one wants a 'local' ring in a location very distant from the CU and wants to avoid VD (or even Zs) problems. It's really then just a 'poor man's version' of running a submain to a local CU - but I see nothing electrically wrong (or even 'poor') about it - and I know of nothing in the regs which forbids it (provided, as you say, cables and OPDs are correct).

When I moved into my current house (25 years ago), I had a couple of such circuits - the imperial equivalent of a 2.5mm² ring on the end of a very long (imperial equivalent of) 10mm² feed cable from a 30A fuse.

Kind Regards, John

 

[ericmark]

I have argued many times over this.

433.2.1 Except where Regulation 433.2.2 or 433.3 applies, a device for protection against overload shall be installed at the point where a reduction occurs in the value of the current-carrying capacity of the conductors of the installation.

To me feed in 6mm then split into two 2.5mm cables may be a change in cross sectional area but not current-carrying capacity so would be allowed. Clearly as a cable enters or leaves a insulated wall we don't add MCB's but treat the circuit as a whole so the same goes here.

Personally where there is likely to be a volt drop using even thicker cable to reduce volt drop or loop impedance would be in order but the problem arises where in the future some one may see a heavy cable and use a larger than 32A MCB.

I find the argument that some one may in the future do something wrong rather flawed as one can't really ever guard against what some one does in the future. However having said that we should always leave as as built plan and test data with notes. Clearly we can't stop owners loosing it after but today I suppose many records are kept by the LABC so in the future we could request assess to them?

I had a similar problem with my parents kitchen the house needs a re-wire but my dad refuses to allow it to happen says at 88 does not want the mess and it will be good enough for his live time. Likely true. But to install a new kitchen we clearly needed to follow current regulations including fitting RCD protection which is of course required for any new sockets. As with your problem best idea would be heavy cable to feed kitchen so we used a SWA cable outside the house clipped to wall to feed a mini consumer unit in the kitchen.

There was in our case a second problem in that my mother in a wheel chair could not access the existing consumer unit under the stairs and RCD's do from time to time trip without there being a fault so the mini consumer unit was placed where she could reach it.

My only problem with what you want to do is who is inspecting? Clearly new circuit so will come under Part P so either LABC and/or the scheme operator will need to accept the paper work. To argue after the event is hard so I would advise ask your scheme operator or LABC which ever is the case if they will accept this method.

Although I see nothing wrong my son did on a job we were doing together so clearly not all people consider this is acceptable. So ask before you do it rather than after to ensure they will accept it.

 

[JohnW2]

Currently in addition to the main ring main there is a 6mm radial which runs in the ceiling space to the otherside of the house where it terminates in a large round junction box in the ceiling space, which I have found and made an access hole to. From that there are five runs of 2.5 twin and earth, one goes to a double socket, one goes to a fcu which feeds the boiler, one feeds the downstairs loo light, and the final two run on, via a pair of junction boxes (presumably cut the cable too short) , to three double sockets in a ring around the conservatory which contains the washing machine and drier.
It would not be a hard job to move the loo light to onto the downstairs lighting circuit. But obviously to extend the ring back to the consumer unit would be a right pain, as would rewiring the conservatory as continuation of the radial because its all plastered in. Therefore my best thought is to crimp on an extension to the 6mm radial and run it down by the side of the boiler, where I can have an accessable junction to start the ring, which can be made to include the FCU and the socket.

I'm not sure that I understand why you are contemplating those changes and/or how you feel those changes would improve the situation. IF one accepts the concept of a 2.5mm² ring fed by a single 6mm² cable (lollipop style), protected by a 32A MCB, then I don't see any real problem with having an unfused spur (to the double socket) and a fused spur for the boiler both coming from the 'origin of the ring' (end of the 6mm² feed cable). The same would even go for the feed to the loo light if it was fed via an FCU. The only real 'improvement' I see resulting from your proposal (if I understand it correctly) is that the boiler FCU and double socket would then be part of the ring - maybe 'nicer' in ideal design terms, but there's really nothing wrong with spurs.

Am I missing something?

Kind Regards, John

 

[JohnW2]

I have argued many times over this.
433.2.1 Except where Regulation 433.2.2 or 433.3 applies, a device for protection against overload shall be installed at the point where a reduction occurs in the value of the current-carrying capacity of the conductors of the installation.
To me feed in 6mm then split into two 2.5mm cables may be a change in cross sectional area but not current-carrying capacity so would be allowed.

I don't think that's the real issue with the 'lollipop' circuit - even if one thought about a reduction in CSA as invoking 433.2.1, a combination of 433.2.2 and 434.2.2 would normally allow a circuit which reduced in CSA somewhere along its length to be protected only at the origin (i.e.CU), provided that the MCB rating was low enough to protect the cable beyond the CSA reduction. However, as I see it, the main potential 'issue' is that, under normal circumstances, it's not acceptable to have 2.5mm² cable protected only by a 32A MCB. As you know, 2.5mm² ring final circuits protectedby a 30/32A OPD are only allowed because 433.1.103 specifically allows such a circuit (provided that CCC of cable is at least 20A).

Although one can argue that nothing in 433.1.103 precludes a ring final having a lollipop design, others may well argue that they believe that 433.1.103 only applies to rings which start and finish at the OPD (usually CU), per the example shown in Appendix 15. That doesn't mean that a lollipop design is 'outlawed' by the regs but, if one takes the view that it is not specifically allowed (i.e. not 'deemed to satisfy' 433.1.1), one would have to be prepared to present one's own argument (with calculations) that 32A protection of the 2.5mm² ring cable was acceptable - presumably in the same manner as the IET did when justifying (at least to themselves!) 433.1.103.

Kind Regards, John

 

[dhutch]

Thanks for all the replies.

The main reason for making the change, effectively just moving the point it diverges into the 2.5, is to place the junction in an accessable place , on the wall by the boiler, rather than plastered into the ceiling void above the utiliy/boiler room as I beleve it is very much non prefered to have conventional jb's in inaccesable locations. You could then incorporate the boiler fcu and the other socket near enough for free as there all in basically the same place.

Moving the loo light onto the lighting circuit just seems the neatest way given the proximity of the other lighting.

Im looking at getting an electrician in to wire up the garage, and am getting some plastering done, so might as well chase the wall out and get it all done while he's here.


Daniel

 

[dhutch]

I presume a crimped/heatshrunk joint joining two peices of 6mm in the ceiling space, with a junction on a wall box, is perferable to a round junction box in the ceiling space.

There is a false ceiling in the kitchen (plasterboard and 4*2 framing) which im looking to remove to open up to the origanal ceiling and the junction box is in this space between the two ceilings at present.


Daniel

 

[JohnW2]

The main reason for making the change, effectively just moving the point it diverges into the 2.5, is to place the junction in an accessable place , on the wall by the boiler, rather than plastered into the ceiling void above the utiliy/boiler room as I beleve it is very much non prefered to have conventional jb's in inaccesable locations. You could then incorporate the boiler fcu and the other socket near enough for free as there all in basically the same place.

Ah, I see - I misunderstood. When you wrote in your OP "...a large round junction box in the ceiling space, which I have found and made an access hole to...", I thought you meant that you had created permanent access to the JB (i.e. with an access panel or somesuch). I agree that, if you want to move the JB for that reason, then you might as well take the opportunity to incorporate everything into the ring.

Moving the loo light onto the lighting circuit just seems the neatest way given the proximity of the other lighting.

Yes, if that's fairly straightforward to do, it also makes sense.

Kind Regards, John

 

[JohnW2]

I presume a crimped/heatshrunk joint joining two peices of 6mm in the ceiling space, with a junction on a wall box, is perferable to a round junction box in the ceiling space.

Yes, but there are now alternatives. Although Ashley mainetenance-free JBs will not take 6mm² conductors, Wago 773-173 connectors in a Wagobox (which is now maintenance free up to 32A) will take 6mm².

Kind Regards, John

 

[Iggifer]

and screwfix now sell Wagos + Wagoboxes

 

[dhutch]

Ah, I see - I misunderstood. I thought you meant that you had created permanent access to the JB.

Sorry, it was open to interpretation, but I have simply chain drilled some holes in the PB so I can see it.

I was first drawn to the fact that there was something slightly a-miss when I realised the loo light wasnt on either of the lighting circuits (I was trying to isolate it to correct a loose connection behind the switch) at which point it transpired the two runs of 2.5 leaving the 'conservatory ring main' mcb where infact only 2ft long and turned into said lenght of 6mm (which was long enough to reach the consumer unit) and that the boiler was also on this ring. At which point I knew there was a junction somewhere and set about to find it. Presumably the previous owner (a builder by trade) and done this to disguise the fact he had reused what might quite well have been an old shower feed when adding the convertory and moving the bathroom upstairs. Didnt show up on the elec survey, could have been less clever if I had not have tested for dead before resecuring the loose wire.

Wago 773-173 connectors in a Wagobox will take 6mm².

and screwfix now sell Wagos + Wagoboxes

Fair enough, yes, only the three way ones, random.
http://www.tlc-direct.co.uk/Products/WA173.html

Feels slightly better to have it crimped and covered in adheasive shrink tube with crimps below as you get some mechanical strenght back. But im sure either works so I guess i dont mind which is used. Presumably they would just use the yellow 6mm crimp joiners, which can take 32amps or more?

http://www.tlc-direct.co.uk/Products/CTBUTTslashY.html


Daniel

 

[Iggifer]

Wago 773-173 connectors in a Wagobox will take 6mm².

and screwfix now sell Wagos + Wagoboxes

Fair enough, yes, only the three way ones, random.
http://www.tlc-direct.co.uk/Products/WA173.html[/QUOTE]

I'm not sure what you're saying about the Wagos. Only the 773-173 will take 6mm² / 32a? If so then yea, but they're massive compared to the others.

From personal experience, it can be an absolute pig to get cables (especially solid stranded) cables out of Wago's when you're actually trying to, so I would be happy to use them in a Wagobox as a MF junctionbox. You have to twist and pull, a lot, to get them out, whereas a crimp you can just pull (hard, admittedly)