Are people moving away from rings

[MG201]

hi all I’m just wondering are the forum members moving away from doing ring circuits and doing radials instead ? I have been reading that this may be the way industry is going wether this is to aid in the introduction of AFDDs I don’t know , obviously AFDDs won’t work in rings, that’s why I recon radials will have to be standard before AFDDs are used.
There will no doughy be some sparks who install AFDDs on rings which will defeat the purpose of them , ( if I’m right )
Should all new builds now be installing radials ??

 

[MG201]

I'll occasionally wire a 4mm ring as well.

What circumstances would you choose this option , I have a good idea but just reassuring my thoughts

 

[Dave OCD]

Well if the overall length was close to max Zs values, or in a kitchen with a lot of appliances- and also installation methods where insulation is everywhere for example. And I also like a bit of 4mm

 

[Toneyz]

The layout of outlets would be a design consideration.

 

[Dave OCD]

Yes that's what I was getting at in a roundabout way.

 

[Lucien Nunes]

I don't install general purpose circuits so I don't have to make this choice, but I would use 32A rings where appropriate if I did. They are an effective and flexible means of providing for a high total loading over a large area with a minimum number of redundant or little-used circuits. Whilst open to some theoretical objections, in practice they have served reliably for over 70 years.

It's important to make the distinction between two choices:
20A circuits vs. 32A circuits.
Ring circuits vs. radial circuits.

Obviously there is no difference in usability between a 32A radial and a 32A ring. But there is a difference between say two 20A circuits and a 32A circuit. Although the total current available from two 20A circuits is higher, you cannot plug two 13A loads in wherever you please, only one can be on each circuit, whereas on a 32A circuit they can be anywhere i.e. there is greater diversity so you can do more with a given total circuit capacity.

Horses for courses, I would say. And there you've got the betting ring, the parade ring...

 

[gnuuser]

Going back into the mists of time I remember being told during my initial electrical training that ring circuits were standard because you could use smaller cable. It was a resource thing following WW2 and it meant limited copper stretched further. I never looked into it any further and it could have been complete bobbins from my instructor at the time but it sounds plausible.

correct and the benefit of the ring circuit was that you didn't have as much voltage drop in the circuit because you had 2 points of supply on the circuit.
this effectively halved the distance calculations for voltage drop that you required for a radial circuit.
less voltage drop= smaller sized conductor being suitable for the job

 

[Deleted member 26818]

Not forgetting of course, that when RFCs were introduced, they were replacing multiple single point radials (each individually sized for the expected load) with a single multi-point circuit that could be used for a variety of loads.

 

[Shoei]

So RFCs aren't compatible with AFDDs because a break in a ring doesn't create an arc. Doesn't that make the ring safer because it's more fault-tolerant?

You don't want a break but better to find it on a routine inspection, rather than wire to increase the likelihood of an arc just so the AFDD can detect it.
Open to interpretation but I'd have thought protection against arcing with a single break is an argument in favour of rings.

 

[Deleted member 26818]

So RFCs aren't compatible with AFDDs because a break in a ring doesn't create an arc. Doesn't that make the ring safer because it's more fault-tolerant?

You don't want a break but better to find it on a routine inspection, rather than wire to increase the likelihood of an arc just so the AFDD can detect it.
Open to interpretation but I'd have thought protection against arcing with a single break is an argument in favour of rings.

Taking on board, that arcs can cause fires, then yes it would appear that an RFC is safer.
However, the fact that a break in the circuit would be undetectable and could cause one of the legs to be overloaded, which could also cause a fire, kind of negates the safety side of no arcs.

 

[Shoei]

Taking on board, that arcs can cause fires, then yes it would appear that an RFC is safer.
However, the fact that a break in the circuit would be undetectable and could cause one of the legs to be overloaded, which could also cause a fire, kind of negates the safety side of no arcs.

Fair point, but in real life it's not obvious whether more fires would result from arcs or overloads, worst case for a 2.5mm cable at 32A would be 15.2W/m which is warm but not catastrophic. I don't know, but arc faults could be a greater fire risk than overloads in most real installations. I'd like to see UK research-based evidence before calling it either way.

 

[Lucien Nunes]

Has anyone ever seen hard evidence of correctly-installed ring cables damaged by overheating specifically due to a break in the ring? (Obviously discounting localised heat damage from a faulty termination.) I haven't, and I suspect that far from causing a fire, the usual result of a broken ring is that the cables run a few degrees hotter than normal but still less than rated temp. Exceptional outliers where the full 32A load is all on one leg, and the cable installation method pushed the rating in the first place, might get warm enough to have their useful life slightly shortened.

By contrast, we've all seen connections burn up, which is what AFDDs are looking for.

 

[Deleted member 26818]

If we discount the overloading of one of the legs in the event of a break in a conductor, as being a safety issue.
Can we then discount the advice to ensure an RFC is not overloaded during normal use?

 

[Shoei]

If we discount the overloading of one of the legs in the event of a break in a conductor, as being a safety issue.
Can we then discount the advice to ensure an RFC is not overloaded during normal use?

No one has discounted overloading as a safety issue, the observation was about comparative risk from a fault condition. RFCs have a useful safety feature that they suppress arcing if a conductor breaks, but now we are asked to make an arc more likely so an AFDD can detect it. It's fair to ask whether that improves or degrades electrical safety.

What's the greater hazard, a 5000 degree plasma in part of a PVC cable, or a temperature rise of a few degrees along it's length? I don't know the answer but I'd like to see some UK evidence before dumping RFCs and adopting a solution designed for the hazards of American domestic wiring.

 

[Marti]

One of the most informative discussions I've read in here - thank you folk.

 

[Pete999]

Fair point, but in real life it's not obvious whether more fires would result from arcs or overloads, worst case for a 2.5mm cable at 32A would be 15.2W/m which is warm but not catastrophic. I don't know, but arc faults could be a greater fire risk than overloads in most real installations. I'd like to see UK research-based evidence before calling it either way.

Don't protect a 2.5mm2 socket radial with a 32 Amp OCPD should be a 20 Amp, 32 Amp radial will require 4mm2 Amendment 15 BBB.