Radial circuit.

[Russell griffiths]

Can somebody explain in dumbo language what a radial circuit is please as opposed to the old ring main (final)

Hand scribbled diagrams appreciated. 

Edited February 16, 2020 by Russell griffiths

[Jeremy Harris]

5 minutes ago, Russell griffiths said:

Can somebody explain in dumbo language what a radial circuit is please as opposed to the old ring main. 

Hand scribbled diagrams appreciated. 

 

 

John Ward has some details and diagrams here: https://www.flameport.com/electric/socket_outlet_circuits/ring.cs4

 

and here: https://www.flameport.com/electric/socket_outlet_circuits/radial.cs4

 

 

 

 

[joth]

One other thing to note that I don't see mentioned on the linked pages is you can't convert a ring main (also called a ring final) to radial simply by disconnecting the final connection back into the consumer unit.

All cabling used throughout the circuit also needs increasing from 2.5 to 4mm²

https://www.homebuilding.co.uk/electrics-cabling-circuits-and-switches/ (unless the circuit breaker is down rated to 24A)

 

It's the cost savings of using smaller cable that is the reason for popularity of the ring main. 

[ProDave]

11 minutes ago, joth said:

One other thing to note that I don't see mentioned on the linked pages is you can't convert a ring main (also called a ring final) to radial simply by disconnecting the final connection back into the consumer unit.

All cabling used throughout the circuit also needs increasing from 2.5 to 4mm²

 

But you CAN split a ring into two separate radials as long as you change the mcb size, you can usually put the 2 halves on 20A mcb's.  I have done this occasionally to solve a problem on a ring final by disconnecting a damaged section and converting to 2 radials where the disruption needed to replace the damaged section would be too great.

 

[Jeremy Harris]

32 minutes ago, joth said:

One other thing to note that I don't see mentioned on the linked pages is you can't convert a ring main (also called a ring final) to radial simply by disconnecting the final connection back into the consumer unit.

All cabling used throughout the circuit also needs increasing from 2.5 to 4mm²

https://www.homebuilding.co.uk/electrics-cabling-circuits-and-switches/ (unless the circuit breaker is down rated to 24A)

 

It's the cost savings of using smaller cable that is the reason for popularity of the ring main. 

 

 

First off a "ring main" is something the DNO use in their LV power distribution system, and is not something usually found within a domestic installation.  A ring final is the looped circuit used for domestic power distribution.

 

As @ProDave says, there's no reason not to split a ring final into two radials, and there isn't often a need to increase the cable size.  2.5mm² T&E is OK for up to 27 A clipped direct, so with 20 A protection is fine.  It would only need to be increased to 4mm² if there was something causing the cable current carrying capacity to be reduced, like running it through insulation.

 

The original reason that the rather bizarre, and uniquely British,  ring final arrangement was introduced was because of a copper shortage in the 1950's when the new regulations were being framed.  Prior to that British homes had been wired with radial circuits feeding round pin outlets with no plug fuse.  Quite why we've stuck with it is a mystery, as there are a lot of advantages to using the same radial configuration that just about every other country uses.

[Ed Davies]

44 minutes ago, joth said:

a ring main (also called a ring final)

 

Let me rephrase that for you: “a ring final (also widely but incorrectly called a ring main)”, though why we don't just call them “rings” or “ring circuits”, as we do with radials, escapes me; a house will likely only contain final circuits and maybe the odd sub-main.

 

PS: a “lighting ring” is almost never a ring. It's usually a branching radial.

Edited February 16, 2020 by Ed Davies
Add PS.

[ToughButterCup]

1 minute ago, Ed Davies said:

... “a ring final (also widely but incorrectly called a ring main)”, though why we don't just call them “rings” or “ring circuits”, as we do with radials, escapes me; a house will likely only contain final circuits and maybe the odd sub-main.

 

Thank you very much ..... at last.

They know what they know, and since they learned about it so long ago,  they don't know why they know it, so they can't explain it. Why should they? They're not teachers.

 

Wiring: there's nowt more jangling for Know-Nowts like me than a scattering of technical terms all meaning the same thing, spoken by people who seem often to me not to be able to answer simple questions - like

What the difference between a ring main and a ring final then?

 

 

[Jeremy Harris]

24 minutes ago, AnonymousBosch said:

Wiring: there's nowt more jangling for Know-Nowts like me than a scattering of technical terms all meaning the same thing, spoken by people who seem often to me not to be able to answer simple questions - like

What the difference between a ring main and a ring final then?

 

 

A ring main is a wiring configuration that a DNO (Distribution Network Operator, the electricity delivery company) might use in the LV (Low Voltage - typically 230 VAC in this case) power distribution network.  They will sometimes use a ring main in order to reduce the voltage drop, although they are only usually found in an urban environment, where the configuration can work OK without needing lots of additional cable (somewhere like a housing estate, for example).  In rural areas DNOs more often use a radial main configuration.  The cable size will usually be the same for either main configuration, although for a long rural area LV run the cable size may be increased to reduce the voltage drop.  A ring main also gives a degree of fault tolerance to the supply, in that the ring can be broken and power will still be delivered to some end users.

 

A ring final is a domestic wiring configuration where the cable is configured into a ring, fed at both ends.  The reason for using this configuration in a domestic installation isn't primarily to reduce voltage drop, it's to allow thinner cable to carry a current in excess of that which it could carry safely in a radial configuration.  For example, ring finals are commonly wired with 2.5mm² cable, that can safety carry 27 A when clipped direct to a surface.  However the over-current protection for such a circuit will often be a 32 A circuit breaker.  Safety depends on the ring final being complete and unbroken, so that current can be shared around both sides of the ring, from the consumer unit to the outlet(s).  If a ring final circuit is broken it present a potential fire hazard, as the over-current protection device will have a higher current rating than the cable.  It is for this reason that one of the very first checks when doing a periodic inspection is ensuring that the rings are complete, by testing continuity and resistance where they terminate in the consumer unit.

[Russell griffiths]

Thanks all, I thought it was more complicated than that. 

[joth]

7 hours ago, Ed Davies said:

8 hours ago, joth said:

a ring main (also called a ring final)

 

Let me rephrase that for you: “a ring final (also widely but incorrectly called a ring main)”, though why we don't just call them “rings” or “ring circuits”, as we do with radials, escapes me; a house will likely only contain final circuits and maybe the odd sub-main.

 

Right. I'd go as far as say they're universally called Ring Mains by Joe public, so I intentionally kept with that terminology as it what was used in the OP