Ring Final Circuit (RFC) versus Radial. Yes, again.

[Dustydazzler]

When you go into a rewired property and there are 3 RFCs one up one down.

One in the kitchen with drops for the appliances.

Kettle. Microwave, dishwasher, washing machine, usb sockets, toaster, coffee machine etc etc.

Is this where the debate of segregation of circuits come in.

From an circuit isolation POV one could possibly argue a ring with everything on it a poor design but in the real world it really isn't that big an issue. Maybe in a commercial kitchen setting where you only want to isolate part of a kitchen.

 

[mainline]

Its nearly always a burned out joint / terminal that is the issue , as you say usually a cheap carp accessory that burns out and not the actual cable itself.

I'm not anti-Ring, a well installed 30amp ring in 2.5 is bullet proof and will last a lifetime, its the gimps that infect the ring with spurs on spurs where the design faulters

Of the 21 cottages I look after, I only found 2 with RFCs that tested ok.

All the others have/had faults due to add-ons over the years.

Nothing against RFC as such, but I will avoid using where I can, and I think most will.

 

[Dustydazzler]

Of the 21 cottages I look after, I only found 2 with RFCs that tested ok.

All the others have/had faults due to add-ons over the years.

Nothing against RFC as such, but I will avoid using where I can, and I think most will.

Nearly all sparks I speak to over the past few years who do daily domestic and Eicrs IF they come across a broken down Ring they no longer bother trying to find the break they just change the MCB to a 20amp and in effect create a 20amp spider radial.
I rarely install rings anymore if adding a new circuit, I just do a 20amp in2.5 or 32amp in4mm.
I can't actually remember the last time I installed a brand new 30amp ring in a house,

 

[mainline]

From an circuit isolation POV one could possibly argue a ring with everything on it a poor design but in the real world it really isn't that big an issue. Maybe in a commercial kitchen setting where you only want to isolate part of a kitchen.

Difficult to comply with 531.3.2 though.

 

[brianmoooore]

Incidentally, did John Ward not do a video once that tried to burn out 2.5mm cable? Maybe testing the quality of Wagos, etc?

I vaguely remember it taking something quite large like 60 odd amps, etc.

Anyone with a conventional arc welder can recreate this. I've connected up odd lengths of various size cables to my 180A Pickhill when I've been bored.
Try it in a well ventilated area though. The gasses given off are lethal.

 

[mainline]

Incidentally, did John Ward not do a video once that tried to burn out 2.5mm cable? Maybe testing the quality of Wagos, etc?

I vaguely remember it taking something quite large like 60 odd amps, etc.

It was about a meter of 1mm.
At 50 amps it caught fire quite quickly, It seemed fine at twice its rating.

I would like to see one where the cables are in insulation, along with terminations etc and run at twice the rating for a sustained amount of time.

 

[happysteve]

I mostly do additions and alterations, infrequently new circuits, very rarely (partial) rewires. I've installed RFCs in new installs where voltage drop would have otherwise been an issue (e.g. upstairs sockets on large area 4-bed house), but otherwise install radials where I can.

The issue with RFCs, even correctly-installed ones, is you never know what you're going to find, which makes it harder to do a quote for a trivial job of adding another socket, because you never know (visually) if an existing socket it on the ring, or a spur. Yes, you can turn the circuit off, have a look behind, and check r1 rn r2, but that's a fair bit of faff when you're just popping round to do a quote. If it's a B20 or B16 supplying a radial circuit, then I smile because I just do a quick Zs check at the socket I'm going to extend from and - other than insulation resistance - the number of unknowns is massively reduced.

A typical case will be adding an outside socket on the back wall of the house, where there's an existing socket in the kitchen cupboard (or behind the washing machine). If it's on the ring - great! Add a DP isolator (or 13A SFCU), drill through the back wall, and away you go. If it's a spur? Sure, could add a 13A FCU to feed the existing socket, plus the new outside one... but what if the existing spur is a 2G socket that feeds a dishwasher and washing machine (or worse, tumble dryer)? The 13A FCU will end up working beyond its capacity, whereas the unfused spur supplying the two appliances on the existing 2G socket would have been fine.

So I propose a new Regulation:

433.1.205: Unfused spurs on a RFC should be clearly marked as such, either using a permanent label, or a small indication in the bottom right hand corner of the plate that can be seen with a UV light or similar​

I sleep soundly at night adding a 3A SFCU feeding an outside LED light (or a doorbell) to an unfused spur (with an existing 1G or 2G socket on it)... doesn't match the guidance in Appendix 15 (Informative), but does comply with 433.1.204 as the few extra mA of current are not going to make a jot of difference to the safety of the unfused spur.

 

[mainline]

 

[pc1966]

Yes, that is what I remembered seeing. Thanks!

 

[pc1966]

So I propose a new Regulation:

433.1.205: Unfused spurs on a RFC should be clearly marked as such, either using a permanent label, or a small indication in the bottom right hand corner of the plate that can be seen with a UV light or similar​

Sadly most of the problem additions will be done by folks who have never read the regs at all!

I sleep soundly at night adding a 3A SFCU feeding an outside LED light (or a doorbell) to an unfused spur (with an existing 1G or 2G socket on it)... doesn't match the guidance in Appendix 15 (Informative), but does comply with 433.1.204 as the few extra mA of current are not going to make a jot of difference to the safety of the unfused spur.

Indeed, while not how things should be done it actually presents no risk of overload/overheating.