Are people moving away from rings

[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.

 

[Flanders]

Deleted duplicate post

 

[Flanders]

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.

Looks like we need John Ward to do one of his experiments

 

[Mike Johnson]

I suppose eventually we will adopt the EU standard of dual MCB's and spur's, together with dedicated spur's for appliances, Brexit accepted.

 

[Mike Johnson]

Duplicate post?

 

[Pete999]

I suppose eventually we will adopt the EU standard of dual MCB's and spur's, together with dedicated spur's for appliances, Brexit accepted.

By Dual CBs I presume you mean DP CBs, as for appliances on their own dedicated circuit, a good idea in my book especially for the larger appliances greater than 2KW as an example.

 

[Shoei]

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.

Agree, those numbers illustrate worst case if you have a 32A protected 2.5mm RFC, and it breaks somewhere, putting max current on one sector of the ring.

 

[Mike Johnson]

Most of the special circuits, that should be on an individual DP CB if I can remember them all are:
Washing Machine
Tumble Dryer
Oven
Hob
Dish Washer
Water Heater
UFH
Fridge On separate RCD
Freezer On separate RCD
Alarms
Outside dependancies
Garage
Electric heating inc ASHP
Towel Rails
Extract Fans
Max of eight sockets on 1.5mm protected by 16A
Max of twelve sockets on 2.5mm protected by 20A
No ring mains allowed
All lighting to have an earth running to them even if not used
Everything metal has to be earthed even if built into the walls
No T & E allowed all cables must be double insulated and of the same cross section
That's all I can think of at the moment, but if anyone is interested PM me and I can direct to the best information source.

 

[chrisdungan]

I'm a Kiwi sparkie ( actually a registered electrical inspector). I've worked in Eire and the UK 2007/8. in our part of the world ring circuits are almost completely unknown in domestic. Probably for the same reason you guys do rings. "Because that's the way we've always done it........"
There are pluses and minuses in both systems.
Here we usually wire our radial circuits in 2.5 stranded, the cheapskates will use 1.5. Yes I know seems weird to you guys but we wire domestic lighting circuits in 1.0mm. the only time we use solid conductor is in 1.omm all the other sizes are stranded!
So modern kitchens usually have 2 circuits with a separate circuit going to the separate laundry. In kiwi land we don't put clothes washers in the kitchen, they go in a serarate laundry room or a laundry space in the garage ( usually a double or treble in a bigger house)
These days that 2.5mm circuit will often be rated at 16amp rather than 20 because of our derating factors due to thermal insulation. RCDs are required and now AFDDs are becoming the norm.
Faultfinding and testing with radials is a breeze.
The only downside with a house full of radials and a switchboard full of CBs, RCDs and AFDDs is you need a minimum of 45 ways. 60 ways if you have PV and you live in the country with a water pump and septic disposal system. There are even some councils that now require rain water storage and pumping for non potable water like toilet flushing and garden watering in town.

 

[Deleted member 26818]

Have they done away with Licencing for Electricians now?

 

[Mike Johnson]

No you don't need a licence to be a SA