Anyone ever seen a 4mm ring circuit like this??

[Engineer54]

As anyone come across a 4mm + 2.5mm RFC protected with a 40A RCBO??
Your opinions please....

 

[axel132132]

Thats a negative ive seen plenty of Radials done in 4mm i have seen one ring but that was protected by 32A RCBO rather than 40A

What loading does it have on it, is there high load on the ring or just couple of sockets for TV's and lamps?!

 

[SirKit Breaker]

I would drop the RCBO to a 32a, but otherwise i dont see any problems. I wouldn't do a ring in 4mm, it will be real donkey work terminating the ends into the sockets, especially if there are any single gang one's.

Cheers...............Howard

 

[Engineer54]

That's a negative Ive seen plenty of Radials done in 4mm i have seen one ring but that was protected by 32A RCBO rather than 40A

What loading does it have on it, is there high load on the ring or just couple of sockets for TV's and lamps?!

Potentially 12KW...lol!!

 

[MDJ]

I would drop the RCBO to a 32a, but otherwise i dont see any problems. I wouldn't do a ring in 4mm, it will be real donkey work terminating the ends into the sockets, especially if there are any single gang one's.

Cheers...............Howard

Hi-Howard,

I have wired dozens if not hundreds of rings in 4mm2, at commercial + Industrial level of course, and it is easy to use, anyhow back to the original question, is it really a problem I wonder?

 

[Engineer54]

Perhaps i should expand on this a bit. ...All loads are cooking appliances ranging from 2.2KW X 1, 3KW X 1, 3.5KW X 2...

This is for a workers kitchen, so no-way domestic...lol!!

 

[MDJ]

Can't see the problem myself, the cable should be able to handle the load, seems fine to me although unusual I suppose, can't say Ive seen a 40 amp ring before, but again no issue, unless theres a reg somewhere I haven't seen.

 

[SirKit Breaker]

Hi-Howard,

I have wired dozens if not hundreds of rings in 4mm2, at commercial + Industrial level of course, and it is easy to use, anyhow back to the original question, is it really a problem I wonder?

Good point, now you come to mention it. I now remember doing a PIR on a car repair workshop, and the workshop sockets were all 4mm SWA, and they were also rings. Cant remember what protection they had, was probably rewireable fuses, its that long ago.

Cheers............Howard

PS my memory is an age thing!

 

[SafetyFirst]

Hi E54, Is the installation 240V single phase or 415 3 phase?

How often are the cooking appliances on? are they maxed out all together sometimes or running on low to medium heat mostly?

If they're a busy outlet then a better setup may be in order IMO.

 

[Engineer54]

Let's say 220/230v single phase, they will all be used twice a day, can't really say how long for maybe 3 or 4 hours at a time. I would imagine a mixture of the two senerio's full wollop to kick off with, followed by medium heat... but i honestly can't say for sure!!

 

[SafetyFirst]

What are you doing there? a PIR?

 

[Engineer54]

Seeing as this has only just been put in, i wouldn't call it a PIR!!

I'm just asking for members opinions at the moment. The for and against brigades if you like, and the reasoning for the For or Against!! ...lol!!!

 

[SafetyFirst]

Well you never said how old it is tbf matey. I personally don't like the sound of it. It's probably safe enough as i'd imagine some diversity can be taken into account but what if there's a fault on that circuit? It'd be shut up shop time. Surely they would be better off rewiring or splitting the loads up somewhat.

 

[ackbarthestar]

We used to do work for a building company who specialized in prefabricated partition walls filled with insulating foam and designated conuit runs already assembled. Their specification was to use 4.0mm2 for all rfcs and 1.5mm2 for all lighting circuits.

I can't see a problem with the design myself.
1/ Its not a domestic installation so its up to the designer to make the call, not building control !
2/ Its not a rfc supplying socket outlets so app 15 is out the window and even if it was the circuit is protected effectively from both overload and earth fault currents. Just leaves installation methods and the effects of heat on the cable in enclosed spaces

Otherwise, its a lot of 2.5,4.0 and 6.0 mm2 radials.

 

[Adam W]

I've never come across one, but if you can wire a ring in 2.5 on a 32A breaker I don't really see the problem with upping the size and using a 40A breaker on a 4mm ring, apart from it not being one of the standard circuit arrangements out of the back of the OSG that's used for domestic properties.

 

[SafetyFirst]

Ackbar states the important fact, thermal effects. Whats the design of the cable run like E54?

Each to there own but as i say i'd have done it differently.

 

[Rockingit]

It's amusing this thread appearing, as I've been toying with exactly the same question for a while.

Personally, I can't see any practical reason not to - I haven't got the book with me to look up the figures to do the maths (and I'm sure you've done that already anyway!) - but it stands to logic that if 1 x 2.5mm will sustain a 20A radial, and 1 x 4mm will sustain a 32A radial then thats a factor of 8 - therefore if a 2 x 2.5mm ring is good for 32A then a 4mm one is good for 50A (subject to method, of course).

 

[SYKRAPS]

We have wired 4mm t+e ring finals on many occasions in domestic situations, due to the de-rating of 2.5 t+e running through 100mm + of loft insulation (in bungalows roof voids) thus enabling us to install the ring final on a 32a mcb/rcbo. I would be a bit dubious installing 40a protection though but I suppose it would depend on the installation method employed and external influences.

 

[benji]

well just think heating elements and rcd/rcbo can give problems one appliance trips and youve lost the lot ,should be on radials

 

[martinh287]

I agree with safety first in that if there is a fault on the circuit it is shut up shop time but can not see any other reason why not to run 4mm ring on a 40a as long as thermal effects are covered