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Discuss Ring final circuit vs Radial final circuit in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

M

mandinga1975

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Hello all

I am sure there is an easy explanation but I am curious ...

Would be interested to know whether there is any major differences between the Ring final circuit and the Radial final circuit.

I am currently studying my NVQ 2330 level 2 and the only difference I can see from the wiring diagrams is that the phase, cpc and neutral go back to the consumer board with the Ring and doesn't with the Radial.

Is there something that the phase, cpc and neutral do when they are wired back to the consumer board on the Ring circuit?

If they don't then why is it used as it seems that it's just a waste of wiring!!

Cheers and apologies if it's something very simple (it's not explained very well in my course notes).

Mandinga
 
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S

simonatlondon

  • Thread Starter Thread Starter
  • #2
Hello mandinga,

the point of a ring final circuit is to use a particular size cable to carry more current than it would if it was a radial circuit. This idea apparentley came about after the 2nd world war. To save on copper wires.

Now the maximum amount of current a 2.5mm T&E is 24 amps. If we are using 2 cables to go to each point of that circuit, then in theory, you can pull twice as much current. Its actually a little less, thats why we use a 32a mcb for a 2.5mm ring circuit not a 40a or 45a. Remember we must always protect the cable from exceeding its current carying capacity.

So 20a mcb for a 2.5mm radial and 32a mcb for a 2.5mm mcb.

Also because the circuit is a ring, the resistance of that circuit is half that of a radial (in theory) and therefore providing a lower r1 + r2.

Hope that helps mate. Sorry, not too great at wording things I want to say.
 
S

simopesh

  • Thread Starter Thread Starter
  • #3
Ring final circuit has virtually no voltage drop and it is mainly used in dwelling larger than 100 square meters. (If my memory serves me correctly)
However, if you use a 4.0mm twin and earth as radial the specs are almost the same as on a 2.5mm ring final circuit.
 
H

hughesy

  • Thread Starter Thread Starter
  • #4
a ring is also one of 2 instances in a domestic premises where diversity is allowed ie a a 2.5 protected by a 32a mcb the other is the 0.5 flex on a ceiling rose protected by whatever protects the lighting circuit ie 10a mcb this is allowed as the light bulb wont pull more current than allowed on a 0.75/0.5 2c flex from a ceiling rose.Hope ive not confused things not very good at using the right words.
 
S

simopesh

  • Thread Starter Thread Starter
  • #5
The radial's phase,cpc,neutral does go back to the consumer unit otherwise it would not work.

Its not a waste of wiring but a valid point on cost. Interesting to note wether 4mm radials would equate to the same cost as rings. AND alot less hassle and confusion.
4.0 mm twin ant earth cost twice as 2.5mm twin and earth. The trick is that you are using only half the length when building a radial with it and it is also quicker to build. Majority of my rewires in the last 6 years are done with 4.0mm radial - 32amp fuse. No faults found!
 
S

sivoodoo

  • Thread Starter Thread Starter
  • #6
2.5mm is easier to work with too :)
 
J

JulesHurley

  • Thread Starter Thread Starter
  • #7
I have done some research into this, and from distant memory, the english love of ring mains being able to supply 32A, is to enable us to use "two bar electric fires", just as our Gran had!

I am a strong beliver that the only area that needs 32A ring main is the kitchen / utility. I prefer to fit circuits for bedrooms etc as 16A radials. May need one or two more MCbs.

From memory, we are one of the only countries that still exist on using Ring mains.
 
M

marshr02

  • Thread Starter Thread Starter
  • #8
Totally agree with JulesHurley. There is however a lot of resistance to moving away from the ringmain cct. It was an excellent ecomomic solution after the war to design ccts that could be used for heating while using least copper. Now we would use radial on Economy7 if using electrical heating...
 
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sivoodoo

  • Thread Starter Thread Starter
  • #9
...so, whats the negative aspects of a ring cct? Apart from more cable clips.
 
M

marshr02

  • Thread Starter Thread Starter
  • #10
- It's overkill in terms of cable runs, when a 32A cct not required i.e. bedroom. Sometimes the topography of a building can make a cable ring uneconomic, and the cable run stops being a ring, more like a doubled up loop.

- the ring can become broken, say due to intermittent connection. The cct is now dangerous, but the fault is not apparent. I wonder how many ring ccts are in this fault condition?

- this is a minor one, but maybe of increasing issue; in a radial cct with no borrowed neutrals etc the flow & return currents are alongside each other - in the ring there can be a large area between flow & return currents, hence increasing EMI interference within the home.


Don't get me wrong. The ring circuit can be an excellent solution in a true 'power' cct where the topology suits a ring cable run..
 
...so, whats the negative aspects of a ring cct? Apart from more cable clips.
Radials are easier to test,can tee off with less restrictions than on a ring,easier to wire,less cable(sorry these are all positive aspects of a radial,just turn that about)
 
P

PhaseShift

  • Thread Starter Thread Starter
  • #12
A ring circuit would be the equivalent of running conductors in parallel. If one conductor becomes open on one side, then more current must flow in the other wire. Seems like the potential exists for more current to flow on a wire that isn't rated for it. The circuit would appear to operate normally until it failed completely or catastrophically.

In the U.S, we aren't allowed to parallel conductors unless they are 1/0 or larger. I don't know what that translates to in mm^2. And when we do, they must be the same length, same material, same insulation, same size, and terminate in the same manner. This is usually only done for services, or large equipment in industrial applications.
 
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PhaseShift

  • Thread Starter Thread Starter
  • #13
Strange coz flex has multiple strands for each conductor and in effect they are in paralel
By flex, do you mean stranded wire? If so, each strand is in intimate electrical contact with every other strand, forming effectively one conductor. I would say that a stranded conductor, and two insulated conductors in parallel, are different animals altogether.
 
L

lawsonium

  • Thread Starter Thread Starter
  • #14
Hello, first post on here for me :)

Sorry to hijack your post but it is related... Promise ;-)

This is a perfect thread for me. I have just bought my first house and I am really excited about doing most of the work myself.
I'm not a newcomer to DIY and have installed a few additions to several electrical installations since I was quite young.

I googled my first big question about my newly acquired house circuit just now which was Ring versus Radial circuits :) haha.

I have identified that my house has been wired in the last 10 - 15 years by the local authority before it was bought by the previous owners and they appear to have installed a radial setup.

I was thinking that this was probably insufficient if I wanted to expand the usage of the system (e.g. new sockets, lights, spurs to outhouses etc) but after reading this thread I am now thinking that the radial setup is actually better suited to increasing the installation.

What are everyone's thoughts on this and what limitations should I consider?

There is also an Economy 7 system installed which is also on a radial circuit. One of the things I'd like to do with this is run an extension from one of the storage heaters into the outhouse to run the washing machine after 12 midnight. What are your thoughts on this?

Kindest Regards,

Matt.
 
G

Guest123

  • Thread Starter Thread Starter
  • #15
Do you intend to notify local building control before you do any electrical work on your house???

Dont get me wrong I dont mind giving anyone a few pointers but technically your not allowed to do much more than change a plug without notifying these days.

As for spurring off an existing storage heater circuit - definately not!!!! those heaters use a lot of power which is why it's one circuit per heater.
 
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