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

[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!!