Changing a Radial Circuit to a Ring Main

T

TomBridges

Hi Everyone,

I have had a New CU fitted in a victorian semi (protected by MCB).

The house needs rewiring which has fallen to me.

Currently I have extended the existing Radial Circuit downstairs, from 2 sockets to 6.

If I want to run from the last socket back to the CU, to turn it into a Ring Main, can I attach this wire to the CU myself? or would I need an electrician to attach it to the CU?

Cheers,
Tom
 
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TomBridges

Well there isn't a need for any more sockets downstairs, and as I understand it, the ring would mean there is less stress on the inital cable (it being split between the 2 instead).. and the ring would be protected by a 32amp mcb instead of the 20amp it is currently protected by.
 
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Do you need more than a 20amp circuit, you say you have already added/extended the circuit to add more sockets, this circuit does it serve the kitchen?
 
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I personally think you are creating yourself unnecessary work, changing a radial to a ring circuit.
But to answer your question, you can do it yourself, but as the circuit will no longer be a radial and then becomes a ring final, the rating of the breaker will be upgraded and then becomes a new circuit, it is then notifiable to building controls.
Link for you to ponder.
http://www.diynot.com/wiki/electrics:part_p
 
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Don't bother. Radial circuits are sound engineering design, ring circuits are a terrible cowboy design.

You have no need for more than 20a on this circuit, so why change it?

It also makes adding any further outlets in the future much much easier, and it's impossible to overload a radial due to poor load spreading or a loose connection (but this is very possible on ring!).


In short,
Radials = good
Rings = bad

You have a radial = :cool:
 
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Do you have any engineering facts to support that statement ?

Yes.

In order to install a ring circuit protected by a 32a OPD device, the cable must have a CCC of only 20a. The HUGE assumption being that in all cases the load will be nicely balanced so as no more than 20a will flow in each leg. A simple fault such as a loose connection somewhere (or a DIYer splitting the ring in the future) will NOT manifest itself, as all outlets will continue to work, however now you can have 32a on a 20a cable.
Even with the ring intact, if there are heavy loads at one end of the ring, it's quite easy to see that more than 20a will flow on that cable (one ring for downstairs, CU next to kitchen - for example).
They are more difficult to test.
It is much more complicated when it comes to adding outlets, and if not done properly (as is all to often the case - spurs from spurs etc) creates other overload dangers.

They were introduced after WWII as a cowboy measure to save on copper, there's no great shortage of copper now, but they remain because of the good old British "we've always done it like that" mentality.


Do you have any engineering facts to refute the statement?
 
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I agree with you on some points, but the fact is that it is no different to any other circuit in that as long as it is properly designed and installed then no problem. Anyone inexperienced can make a mistake on any circuit (reverse polarity, loose connection on high current loads etc) and a so-called 'cowboy' designed circuit should not be blamed for someone's lack of research/understanding of that circuit before carrying out works on it.
 
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HI Loverocket/ricicle,

I agree with both of you.

Having wired a number of rental properties, i would always choose radials over rings where it makes sense.

..Easier/quicker to test
..less chance of abuse by tenants deciding that they can just put an extra socket in, breaking the ring.
..makes more sense considering and applying 314.1 and generally having more ways in a modern C/U
.. less chance of a tenant calling saying that lots of their sockets don't work, less chance of that call turning into an expensive out of hours sparky visit.

perhaps the only normal exception to that would be supplying devices in a kitchen, where there may be a greater chance of seeing a high load.
 
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Tom B,

How many ways (used and spare) in the new c/u?
How big is the house?

If you are rewiring the whole property, you might want to reconsider your layout, depending on answer to the questions above
 
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I agree with you on some points, but the fact is that it is no different to any other circuit in that as long as it is properly designed and installed then no problem. Anyone inexperienced can make a mistake on any circuit (reverse polarity, loose connection on high current loads etc) and a so-called 'cowboy' designed circuit should not be blamed for someone's lack of research/understanding of that circuit before carrying out works on it.
1) True, but in a domestic environment you know that the circuit will, at some point in the rest of its life, be fiddled with by someone insufficiently skilled, and to say "well they shouldn't so I won't allow for that in my design" is a bit like building a motorway with no Armco because people shouldn't cross the central reservation. Ring finals bring very few benefits, but they do bring a lot of drawbacks and potential for dangerous modifications.

2) If we had never had them, if all the world had ever known was the radial, and in a draft for public comment the IET suggested that the next version of the regulations would allow socket circuits to be installed with 20A cable on 32A breakers as long as it was a ring, and as long as you could be sure that you wouldn't get a lot of current in one part of the ring for long periods, and as long as people didn't add more than one socket outlet to unfused branches in the future, do you think the prevailing opinion would be:

a) Fantastic - what a great idea, why did nobody think of this before?

or

b) WTF? Are you mad?
 

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