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

 

[yellowvanman]

E54 you sure the CPC is 2.5mm? 4mm T&E here in the UK is 4/1.5, not that it affects the discussion.

A 32A ring in 2.5mm has to have 20A current capacity on all legs. Not sure where the 20A for 2.5 comes from, but in Table 4D5 20A on 2.5mm compares to 26A on 4mm (ref Method A)

Using the 20/32 ratio, if you've got a minimum 26A CCC on each leg the OPD could be up to 41.6A. Could be higher if you know the CCC of each leg is higher.

 

[tigerpaul]

I've seen 4mm rings with 2.5mm cpcs before. Wired in singles a long time ago before copper was so expensive.

However in your situation I would have thought dedicated radials would be the more obvious choice.

 

[vjsmarwick]

I have fitted a 4mm ring fused at 32A because of the distance from the consumer unit but that's only reason

 

[shagbite]

i think i've read this a bit differently to you lot. i thought he was saying the circuit has one 4mm leg & one 2.5mm leg. if so, i'd be inclined to treat it as a standard 2.5 ring, and drop the 40amp to a 32amp.

 

[Guest55]

my 2p
there is no problem in doing a 40a ring in 4mm , seen it and done it in warehouses with a large floor areas.
but its the connected loads that are of concern.
is it not still standard practice to put loads of 3kw and above that are on for lengthy periods on individual radials ?

 

[SYKRAPS]

i think i've read this a bit differently to you lot. i thought he was saying the circuit has one 4mm leg & one 2.5mm leg. if so, i'd be inclined to treat it as a standard 2.5 ring, and drop the 40amp to a 32amp.

I think the 2.5 is the cpc

 

[SYKRAPS]

is it not still standard practice to put loads of 3kw and above that are on for lengthy periods on individual radials ?

I do radials for this on 2KW or above

 

[GLENNSPARK]

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

and if there was loads of insulation under the floor Howard?....as in many newbuilds...

 

[shagbite]

I think the 2.5 is the cpc

looks like you're right. it just seemed a strange question, as i've done a fair few 4mm rings, so they're not that unusual. i thought e54 must be throwing us a googly and trying to make us think.

 

[ackbarthestar]

i thought e54 must be throwing us a googly and trying to make us think.

Did they run the cables along the ground - surely not?

 

[Engineer54]

No, i'm not throwing you a googly. ...lol!!

I found this arrangement in the site contractors workers kitchen yesterday morning, it's not part of the project works as such. Only when i first come across it, it was actually a ''lollipop ring'' (this contractor seems to like lollipops for some reason lol!!) fed by a 3 core 6mm SWA to a metal back box behind a 100X50mm dado type trunking and singles within the trunking. (There is no T&E type wiring over here by the way) I wonder what some would have said about that arrangement?? lol!!

The run from the DB is about 10m Max. There is no insulation problems, as the SWA's are run on a tray and then into a stud partition wall for about 1.5m to the metal back box. The length of the run in the trunking is only around 3 metres, covering only the area under the extraction hood, so no long distances are involved here. Very little chance of a fault appearing on this installation either. The heavier loads are on 20A DP switches. There is another radial 4mm circuit covering 6 double outlets further along the trunking for the smaller kitchen appliances etc not mentioned above.


I'll tell you what i think, later on today (your tomorrow) when i come back on line... lol!!

 

[ackbarthestar]

E54,
IMO, there is no problem with this arrangement. 'Lollipops' are quite common, unless there is more.....

However, if you feel there is some amiss then you then maybe we aught to change your name to E45 and then apply liberally

 

[Engineer54]

E54,
IMO, there is no problem with this arrangement. 'Lollipops' are quite common, unless there is more.....

However, if you feel there is some amiss then you then maybe we aught to change your name to E45 and then apply liberally

Did i say that i had a problem with lollipops etc??

No, there is no more that i can think of as being relevant...

 

[SafetyFirst]

Well lets just hope theres's never ever a fault around the 10am time!!

The contractors will have to settle for salt and pepper sandwhiches!lol.

 

[ackbarthestar]

Its really a question of probabilities.

Running radials in T&E on tray is not such a good strategy and more likely to get damaged, unless you either cable tied them or ran them in SWA and that would require a lot of fiddling about at the kitchen end.

You could just run a sub-main to a kitchen DB. which again would require more work and also leave the protective devices open to environmental degradation.

It seems an obvious solution to me.
1/ Its quick to install
2/ No environmental damage to the supply and final circuits

 

[Engineer54]

Its really a question of probabilities.

Running radials in T&E on tray is not such a good strategy and more likely to get damaged, unless you either cable tied them or ran them in SWA and that would require a lot of fiddling about at the kitchen end.

You could just run a sub-main to a kitchen DB. which again would require more work and also leave the protective devices open to environmental degradation.

It seems an obvious solution to me.
1/ Its quick to install
2/ No environmental damage to the supply and final circuits

As stated there is NO T&E cables used over here. All wiring is either SWA, or singles in containment, in this case PVC trunking !!

 

[shagbite]

As stated there is NO T&E cables used over here. All wiring is either SWA, or singles in containment, in this case PVC trunking !!

i worked with a team of italians, on a big industrial site a couple of years ago. they said that they'd never worked with swa before. apparently it's not used over there.

 

[Engineer54]

i worked with a team of italians, on a big industrial site a couple of years ago. they said that they'd never worked with swa before. apparently it's not used over there.

That's the Italians for you!!! lol!! Seen a few nightmare supposidly new installations in Rome....

 

[SPARTYKUS]

Sounds fine. The standard circuit layouts in the regs do not preclude other designs, domestic or otherwise!

I have installed a 4.0mm2 ring before. Zs was amazing.

 

[Engineer54]

And now the latest, ...lol!! Went to have a look just before lunch time today, and the head cook has decided he wants more equipment to be connected to this 4mm ring, another 9KW of deep fat fryers (3 No) no less!! So the upstart is, that they are now installing another 4mm ring to this area.

I by the way, have no objection to the 40A rcbo 4mm FRC's. The change from lollipop ring to standard ring, was the call of the contractors supervisor. Which may of been based on me not allowing a similar arrangement in a project building!! ...lol!!

 

[shagbite]

And now the latest, ...lol!! Went to have a look just before lunch time today, and the head cook has decided he wants more equipment to be connected to this 4mm ring, another 9KW of deep fat fryers (3 No) no less!! So the upstart is, that they are now installing another 4mm ring to this area.

I by the way, have no objection to the 40A rcbo 4mm FRC's. The change from lollipop ring to standard ring, was the call of the contractors supervisor. Which may of been based on me not allowing a similar arrangement in a project building!! ...lol!!

all this talk about deep fried lollipops is making me hungry.

 

[SafetyFirst]

Have they only got 4mm cable on that site or something???