Can I join 2 radials to make a ring?

[Longhorn]

Well, I guess that's true of many of us here. If I'm safe just to extend the radials ad nauseam then it looks like we're in business. I'll make sure there's a 20A MCB on each.

 

[telectrix]

Well, I guess that's true of many of us here. If I'm safe just to extend the radials ad nauseam then it looks like we're in business. I'll make sure there's a 20A MCB on each.

best option would be a bigger CU. if you have. say. a 6 way, get a local spark to quote you for a 10/12 way dual RCD or RCBO board.

 

[Longhorn]

The board we have is a 10-way dual RCB MK board.

 

[telectrix]

that should be big enough for most houses. where you live? fawlty towers?

 

[Sparkingmad]

Might be worth getting a sparks in to test some of the other radials you may be able to convert some of those to ring mains to free up some room in that board. Lol

 

[Longhorn]

We seem to be going around in circles.

There are 10 MCBs, but one is the kitchen ring, one is the cooker, one is the alarm. So now we're down to 7. If each radial should have it's own MCB then theoretically we should have no more than 7 radials. Surely it would be better to have, say, an upstairs ring and a downstairs ring and maybe an outbuilding ring, and still have 4 MCBs left over for other things?

If I can connect the two newer radials as referenced in my original post I can add at least 3 more sockets along the way in very usable places, I just wanted to know it it was safe and legal to do this and whether it constituted notifiable work.

 

[telectrix]

altering circuits is not notifiable. a new circuit is.

 

[Deleted member 26818]

When rings were first introduced, sometimes two 15A radials were joined together to make the ring. If you were lucky, the two 15A fuses would be replaced with one 30A fuse.

 

[Mark42]

Hi Longhorn
What no one has explained yet is why radials can be safer: what you've heard about not spur-ing off spurs only applies to ring circuits, because rings are protected at 32A, so long lines of 2.5mm cable running spurs might mean - if multiple loads are plugged into the spurs - overloading that run of single 2.5mm cable. Genuinely possible, and genuinely dangerous.

Whereas radials on 2.5mm are never protected above 20A (sometimes 16A) so even if you have a hundred sockets on the thing, you can't overload the cable as the breaker would trip first. (Assuming the circuit is not stupidly long, but that's enough detail for now.)

Personally I dislike ring final circuits, and consider them outdated. Others will disagree. In your case I'd definitely go for keeping the two existing radials. You may add as many extra sockets locally as you wish. Make sure you have (or add) 30mA RCD protection. And do NOT connect the two radials together at any point.

Note: In my own house (which is 500 years old and made of wood) I did the opposite to what you're suggesting. I inherited only two 32A rings for the whole place. I started by splitting these rings, junking the 32A MCBs, and converting them to four radials, each with a 16A RCBO.

 

[Deleted member 26818]

Outdated?
If RFCs are outdated, what does that make Radials, which RFCs replaced?
It's not fashion week.

 

[Octopus]

Note: In my own house (which is 500 years old and made of wood) I did the opposite to what you're suggesting. I inherited only two 32A rings for the whole place. I started by splitting these rings, junking the 32A MCBs, and converting them to four radials, each with a 16A RCBO.

I'm guessing you didn't have much loading on them.................. 20A RCBO's may have been a better approach!

 

[Mark42]

I'm guessing you didn't have much loading on them.................. 20A RCBO's may have been a better approach!

Of course.
But whoever put the circuits in run the cables in and out of wattle and daub, up, down and all over the place, with tight bends: I just didn't trust the bloke, whoever it was.
I wanted to be sure that there was no chance, ever, of these hidden and buried wires running hot.
I added new 20A radial circuits for heavier loads, took the immersion heater off the old ring (aargh!) and installed all new kitchen circuits.

 

[Mark42]

Outdated?
If RFCs are outdated, what does that make Radials, which RFCs replaced?
It's not fashion week.

Indeed they did, to save copper.

But 2.5mm is now plentiful, cheap, and WWII is over

 

[kingeri]

Ring finals are not outdated, they are just another option for sparks to use where appropriate. These days I do install more radials than I used to, but rings are very versatile circuits, and where the building layout suits I still use rings when I need the 32A. Mainly kitchens and utilities these days. I don't like 32A 4mm^2 radials, the CCC is too close to the edge. The 32A 2.5mm^2 ring final has stood the test of time, and is far more flexible with installation methods. Fine, 20A radials for living rooms, bedrooms etc. are no problem, but for those areas which need higher current ratings, the ring final is still king for me.

 

[Mark42]

Ring finals are not outdated … rings are very versatile circuits, and where the building layout suits I still use rings when I need the 32A. Mainly kitchens and utilities these days. …

I’m not saying you’re wrong. It’s a possibly matter of personal preference.

Although I would argue that in kitchens and utility rooms, separate circuits for dishwasher, washing machine, tumble dryer, microwave, coffee machine and so on are preferable.

I concede that cost and time may be a consideration in commercial work, but that’s not the point I’m making.

… The 32A 2.5mm^2 ring final has stood the test of time, and is far more flexible with installation methods.

My main niggle with 32A rings is that a single point of failure (broken ring on one conductor - and surely every electrician has found this at some time) may result in a potentially dangerous cable overload which could sit undetected for years.

… I don't like 32A 4mm^2 radials, the CCC is too close to the edge.

I agree. Horrible, pointless things and awkward to connect accessories if the boxes aren’t deep enough. No argument there.

 

[Andy78]

My main niggle with 32A rings is that a single point of failure (broken ring on one conductor - and surely every electrician has found this at some time) may result in a potentially dangerous cable overload which could sit undetected for years.

I have found plenty of non-continuous ring conductors. I have never discovered any thermal damage to cable due to overload caused by this lack of continuity though.

It's a potential hazard that exists only in theory in my experience. It would be interesting to see a bench test however and see how 2.5mm cable performs in this overload situation.
Wonder if JW has ever done this ?

 

[Mark42]

I have found plenty of non-continuous ring conductors. I have never discovered any thermal damage to cable due to overload caused by this lack of continuity though.

It's a potential hazard that exists only in theory in my experience. It would be interesting to see a bench test however and see how 2.5mm cable performs in this overload situation.
Wonder if JW has ever done this ?

Hmm. I don't entirely disagree, but to extrapolate your argument would be to say it's OK to protect buried 2.5mm T&E at 32A. Would you ever do that?

It would indeed be interesting to run, say, two old-skool 3kw fires down a long bit of 2.5 T&E to see what actually happens. I do collect such things, but have enough on this week!

 

[Andy78]

Hmm. I don't entirely disagree, but to extrapolate your argument would be to say it's OK to protect buried 2.5mm T&E at 32A. Would you ever do that?

It would indeed be interesting to run, say, two old-skool 3kw fires down a long bit of 2.5 T&E to see what actually happens.

I would, and have installed 2.5mm cable protected by a 32A device. As a spur from a ring.

2 x 3kW fires on a bit of 2.5mm I would expect to be fine almost indefinitely with regards the cable. It is certainly just under the tabulated CCC of the cable.
If both were plugged into a double socket however, I would expect that to be the weak link as they are only rated at 20A.

 

[Mark42]

I would, and have installed 2.5mm cable protected by a 32A device. As a spur from a ring.
2 x 3kW fires on a bit of 2.5mm I would expect to be fine almost indefinitely with regards the cable. It is certainly just under the tabulated CCC of the cable.
If both were plugged into a double socket however, I would expect that to be the weak link as they are only rated at 20A.

Ha! Yes, correct of course, but you know that's not what I meant.

And sure, I once fused 0.5mm at 200A. For indicator lights in a main incomer switch panel. But I wouldn't use 0.5mm for 200A distribution, even if the budget was tight.

In the very specific case of a short spur or two, you are absolutely right in that the risk really is only theoretical, as no sensible person plugs two 3kW fires into the same double socket, or even in the same room. The radiated heat alone would set the curtains on fire before they needed to worry about the wiring.

My example was ill thought-out. How about a 3kW fire, a 1.5kW washing machine, a 1.5kW dishwasher, then a 1.5kW kettle on a broken long ring buried in insulation? Unlikely, but not impossible. And if it's said that such loads are very rare in practice, then why do we need 32A anyway?

I don't disagree that with quality modern cable, it would probably be OK for years. But I still say that any design which may need to take advantage of over-cautious specs and luck, is bad design!

 

[Andy78]

Ha! Yes, correct of course, but you know that's not what I meant.

And sure, I once fused 0.5mm at 200A. For indicator lights in a main incomer switch panel. But I wouldn't use 0.5mm for 200A distribution, even if the budget was tight.

In the very specific case of a short spur or two, you are absolutely right in that the risk really is only theoretical, as no sensible person plugs two 3kW fires into the same double socket, or even in the same room. The radiated heat alone would set the curtains on fire before they needed to worry about the wiring.

My example was ill thought-out. How about a 3kW fire, a 1.5kW washing machine, a 1.5kW dishwasher, then a 1.5kW kettle on a broken long ring buried in insulation? Unlikely, but not impossible. And if it's said that such loads are very rare in practice, then why do we need 32A anyway?

I don't disagree that with quality modern cable, it would probably be OK for years. But I still say that any design which may need to take advantage of over-cautious specs and luck, is bad design!

The new example given is not really relevant to highlighting the shortcomings of a ring final circuit either.
A 2.5mm twin and earth cable buried in insulation would likely not have been installed to comply with the regulations as this installation method would likely see the CCC below the required 20A at the end of the cable calculation.

I do get your point though and it's very refreshing that you are debating this issue with a bit of thought. Most ring haters really don't know why they do so.

As I say I'd like to see prolonged bench tests of 2.5mm cable under various overload conditions with arrangements simulating non-continuous ring final arrangements of various permutations before I was convinced there is an inherent problem with the standard arrangement.