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

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mandinga1975

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
 
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.
 
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.
 
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.
 
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!
 
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.
 
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...
 
...so, whats the negative aspects of a ring cct? Apart from more cable clips.
 
- 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..
 
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.
 
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.
 
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.
 
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.
 
Last edited by a moderator:
Thanks for your replies...

Do you intend to notify local building control before you do any electrical work on your house???

Is it really necessary to notify them when you are simply wiring in a couple of lights in an outhouse? Surely the proliferation of kits for outside security lights etc etc in popular DIY stores flies in the face of this idea?


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

Well, the property I have is ex local authority and subsequently has been wired and re-wired by the local authority.
There are three separate economy7 circuits in the house, two of them are just a single heater per circuit but the third has (or should I say had) two large storage heaters on it.
I have removed both heaters as they were either side of a wall I needed to put a doorway through. I now have a single circuit with nothing on it (i.e. not spurring off another appliance).

My question was/is, does anyone here think it is a good idea to run this, now unused economy7 circuit, to the outhouse laundry to run the washing machine/drier after 12 midnight?
Also, can you purchase some kind of automatic switch to switch over to economy7 on a timer basis for a fridge freezer?

Kindest Regards,

Matt.
 
Thanks for your replies...



Is it really necessary to notify them when you are simply wiring in a couple of lights in an outhouse? Surely the proliferation of kits for outside security lights etc etc in popular DIY stores flies in the face of this idea?


quote]

Hey Matt.

Probably without knowing it you have hit upon the biggest problem with the whole part P thing since it began.

What you have said is absolutely bang on, how can anyone take part P seriously when all the DIY stores continue to sell electrical equipment to anyone but technically, depending on what your doing and where your doing it it's against the law!!!!!

I'm sure if you look through the forum you will find numerous threads on this very topic.

Anyhow if the circuit is unused I dont see a problem with extending it providing that you make sure the earthing is upto standard and all disconnection times are still met. Bear in mind that the circuit will only be "live" between 12 + 7am so it wouldn't really be practical for a fridge.

Also you would need to check the loading of the washing machine and the drier if they are to be used at the same time, to make sure you dont exceed the current carrying capacity of the cable used in that circuit.

Cheers.
 
Thanks for your replies...



Is it really necessary to notify them when you are simply wiring in a couple of lights in an outhouse? Surely the proliferation of kits for outside security lights etc etc in popular DIY stores flies in the face of this idea?




Well, the property I have is ex local authority and subsequently has been wired and re-wired by the local authority.
There are three separate economy7 circuits in the house, two of them are just a single heater per circuit but the third has (or should I say had) two large storage heaters on it.
I have removed both heaters as they were either side of a wall I needed to put a doorway through. I now have a single circuit with nothing on it (i.e. not spurring off another appliance).

My question was/is, does anyone here think it is a good idea to run this, now unused economy7 circuit, to the outhouse laundry to run the washing machine/drier after 12 midnight?
Also, can you purchase some kind of automatic switch to switch over to economy7 on a timer basis for a fridge freezer?

Kindest Regards,

Matt.

I don't know how technical you are but your fridgefreezer changeover could be performed with a simple relay,suitably rated and installed beside your consumer unit,if you have a dedicated circuit.
 
Hey Matt.

Probably without knowing it you have hit upon the biggest problem with the whole part P thing since it began.

What you have said is absolutely bang on, how can anyone take part P seriously when all the DIY stores continue to sell electrical equipment to anyone but technically, depending on what your doing and where your doing it it's against the law!!!!!

Hi Lenny, thanks for the input. I have to say I tend to get infuriated by all the red tape in the world. Over complicates things. Virtually everything is against the law these days or offends someone.


Anyhow if the circuit is unused I dont see a problem with extending it providing that you make sure the earthing is upto standard and all disconnection times are still met. Bear in mind that the circuit will only be "live" between 12 + 7am so it wouldn't really be practical for a fridge.

Also you would need to check the loading of the washing machine and the drier if they are to be used at the same time, to make sure you dont exceed the current carrying capacity of the cable used in that circuit.

I haven't calculated it yet but I can't see that a washing machine and a drier are going to out load two big storage heaters. I will check the values and cable ratings before I install though, thanks for the warning.

As for the fridge/freezer, I am hoping to implement some kind of relay as per mrloy99 has suggested to automatically switch the power over at the point of changeover.
I don't know exactly how this is to be acheived but I can imagine it is readily available.


I don't know how technical you are but your fridgefreezer changeover could be performed with a simple relay,suitably rated and installed beside your consumer unit,if you have a dedicated circuit.

Hi mrloy99, thanks for your reply. I am keen to know more about this relaying idea. I assumed there would be a device available for this very application as I can imagine it would be commonly required.
Is it better to run an E7 circuit AND a normal circuit to the laundry and have a switch/relay near the utilities or as you have said near the CU, which I am guessing would require using the same cabling to the laundry for both types of supply?

Kindest Regards,

Matt.
 

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