Have the rules for ring mains changed over the years?

[nicebutdim]

Yup in my view good working practices, unlimited 20A radials IMO is just ridiculous

It is and it isn't.

If likely to be subjected to loads in excess of protective device rating, it would be poor design and ridiculous on the part of designer.

If that 20A radial serves three bedrooms in a modern home, with lots of points provided for convenience, then there should be no issue as it's highly unlikely that total load at any given time would trouble the 20A breaker.

Edit: What I do find ridiculous is the idea that anyone might refuse to consider a particular option, because of preconceived notions. I've read a number of comments during my time here to the effect of 'I'd never install a ring' and can't help asking myself why?

 

[mainline]

I still like the flexibility of a RFC

What flexibility does an RFC have over a 4 mm radial ?

as for fault finding them if you know what you are doing it is quite simple.

Trying to reinstate an RFC that's 40 years old with multiple faults isn't always simple, even if you unlike us trainee types know what you're doing.

Dropped the mcd down to 20A because had to break the ring convert to radials temporary.

Jb full of water meant you had to break the ring in two places.

Went back when could take the floor boards up in the area of the damaged section JB full of water.

Better off leaving it as a radial

 

[mainline]

Could be same with a radial and multiple branches. Still have to find the fault and disconnect.
But with an rfc, you might not lose the function of the majority of the circuit until repaired.

One of the problems with an RFC is you may not know there is a fault until you have a fire

 

[7029 dave]

One of the problems with an RFC is you may not know there is a fault until you have a fire

If you twist the legs together this will reduce the risk of , and if it drops out of the socket terminal then in won't work a good reason for twisting RFC IMO for the anti Twister's

 

[mainline]

If you twist the legs together this will reduce the risk of , and if it drops out of the socket terminal then in won't work a good reason for twisting RFC IMO for the anti Twister's

The twisting together of solid core weakens them, so could cause more of a hazard.
I don't think a twisted joint is going to be very good at carrying a decent current.

 

[Pretty Mouth]

What flexibility does an RFC have over a 4 mm radial ?

Installation reference methods. 4mm radials can only be installed ref C (or B if using singles in conduit IIRC), whereas 2.5mm rings can be installed 100, 102, A, B, C.

Also, a much longer circuit length is permitted in terms of voltage drop (106m vs 43m), although obviously both ends must be terminated at the CU. This tends to work well for many domestic socket arrangements, although not in all instances.

One of the problems with an RFC is you may not know there is a fault until you have a fire

OTOH, a ring is less prone to arcing should a loose connection occur, so is probably less likely to cause a fire IMO.

Horses for courses, there are advantages and disadvantages to both types of circuits. I personally am happy to work on rings, and install them where appropriate.

 

[mainline]

Installation reference methods. 4mm radials can only be installed ref C (or B if using singles in conduit IIRC), whereas 2.5mm rings can be installed 100, 102, A, B, C.

Also, a much longer circuit length is permitted in terms of voltage drop (106m vs 43m), although obviously both ends must be terminated at the CU. This tends to work well for many domestic socket arrangements, although not in all instances.

Most domestic circuits can be satisfied with radial circuits.

OTOH, a ring is less prone to arcing should a loose connection occur, so is probably less likely to cause a fire IMO.

Also, less likely for AFDDs to work properly?

Horses for courses, there are advantages and disadvantages to both types of circuits. I personally am happy to work on rings, and install them where appropriate.

I have nothing against the use of RFCs, but would prefer not.

 

[timhoward]

Have no idea how true but the old boys on-site were adamant you should only put 4 sockets max on a 20a radial

If they were old enough to know the 14th edition, there were indeed once such rules in the main regs.

 

[Pretty Mouth]

Most domestic circuits can be satisfied with radial circuits.

Probably, but a ring may be a better option in many instances. If you want a 32A socket circuit for, say, a kitchen, where the cables are installed method 102, then you're looking at either a 6mm radial, or a 2.5mm ring.

Also, less likely for AFDDs to work properly?

I don't believe so. As I understand it, they should detect arcs on a ring just as they would on radial. Hager's take on it:

Contrary to common belief, AFDD’s do offer protection against arc faults in ring final circuits and to the equipment being fed from this circuit. A series arc fault in one leg however, is unlikely to be at a dangerous level so will not be detected. This is due to current in this instance flowing around the other leg of the ring. A series arc fault will be detected in equipment and in flexible cables connected to the ring final circuit. Parallel arc faults are detected and disconnected in all parts of the ring circuit and on all connected equipment.

 

[mainline]

Probably, but a ring may be a better option in many instances. If you want a 32A socket circuit for, say, a kitchen, where the cables are installed method 102, then you're looking at either a 6mm radial, or a 2.5mm ring.

True, but unlikely to need a 32amp socket circuit for most kitchens, radial for sockets, radials, for appliances.
Less nuisance tripping easier to test and safer.

I don't believe so. As I understand it, they should detect arcs on a ring just as they would on radial.

Not true, they cannot detect a series fault in a ring final circuit

A series arc fault in one leg however, is unlikely to be at a dangerous level so will not be detected.

Saying that, the arc is unlikely to be at a dangerous level, doesn't instil confidence.

 

[timhoward]

True, but unlikely to need a 32amp socket circuit for most kitchens, radial for sockets, radials, for appliances.
Less nuisance tripping easier to test and safer.

We seem to have a knack in this country of having limited space for consumer units, and the luxury of 3 RCBOs for a kitchen may not be a given.
Of late, for living rooms and bedrooms I’ve been doing radials, and kitchens usually an rfc.
I don’t mind testing rings - there is something nice about confirming the connections are all good on the points that will regularly see the most current draw.

 

[Dustydazzler]

Rings are great when first installed as a Ring with No spurs etc,
Trouble with rings it comes after years of DIY alterations , they become infected with multiple spurs , become spilt rings / spider rings , faults develop , you get broken legs / lost continuity.
Rings still have a function but I think sooner or later they will become obsolete and we will be using 20a radials for sockets in smaller bunches. Like kitchen radial , lounge radial , bedroom 1&2 radial , bedroom 3&4 radial , hall & landing radial. The days of an entire house being on 1 or maybe 2 rings will soon phase out

 

[pc1966]

Trouble with rings it comes after years of DIY alterations , they become infected with multiple spurs , become spilt rings / spider rings , faults develop , you get broken legs / lost continuity.

That is kind of a false argument, as DIY bodges can make the same issue out of a radial, for example missing CPC that no one notices, swapped L & N, etc.

If faults are in hidden junctions behind walls or under floors it matters not what the intended configuration is (RFC or radial), you still have a pain to find & fix it, or have to abandon that part and put in new cables to get around it.

 

[pc1966]

Less nuisance tripping easier to test and safer.

No, no no! The standard radial test is only easier because you are not doing as much fault coverage.

Do you check the N resistance matches L with a radial to the final socket, and verify that the CPC resistance is in ratio to the L/N? Or just do the R1+R2 look OK for the ADS aspect of the certificate?

You check that as part of the r1, r2, rN of the RFC testing and so have verified there are no high resistance joints along the way, most folks never think to check that with a radial.

Do you check on each socket on a radial that the R1+R2 is very close to the correct value for that (very probably) unknown length of cable?

Probably not, where as with the figure-of-eight test on the RFC you know that every socket's "R1+R2" check should be identical, and therefore any that are high are either a spur (which I agree are bad things for various reasons), or a socket with a dodgy switch or similar.

So while you might prefer "easier testing" on a radial as it saves you time and ticks the box for ADS requirement, you are not doing as comprehensive a test as the RFC permits, and expects, you to do which really does lead to safer installation (e.g. less fire risk from bad connection, etc)

 

[Dustydazzler]

I still believe a radial is a better more simplistic circuit with less potential for future issues.
As I say Rings served a purpose when cable was in very short supply and you need 1 circuit to supply all the socket outlets in the entire house.
In 2023 you can install 4 or 5 dedicated 20amp radials which offer better segrigation of circuits , reduces nuisance tripping and in event of a trip you only lose 3 or 4 sockets rather than the entire house etc