Ring Finals Vs Radials

[JohnW2]

Better off to replace the 2.5 with 4....

Maybe, but as I implied in my previous post, although we hear so much about 32A (or 30A) 4mm² radial finals, that's only actually possible if the cable is 'clipped direct' throughout - otherwise one is up to 6mm², which is probably not (or not often) very practical. This is perhaps one of the reasons why there are still a lot of supporters of 32A 2.5mm² ring finals.

Kind Regards, John.

 

[ericmark]

OK I will admit main reason was I didn't want them to use fan heaters instead of the storage heaters as I was right on the edge of the 300A supply during the day and did not want the fuses to blow in the transformer room as I could not change them. The radial was a good excuse.

As to over 32A then one would need to do ones own calculations and the idea is to use a pre-calculated system be it 20A radial or 32A ring.

As to the kitchen I have said before many so called rings are not really rings but two conductors in parallel as they both feed a grid switch with equal lenght conductors so could be 40A and still be within regulations. Only reason for two 2.5mm instead of one 4mm is can't get 4mm in terminals of the grid switches.

Items which are fixed should have there own dedicated supply which should it would seem include washing machine and tumble drier so if two of the switches on the grid plate have their own supply then why use a ring or conductors in parallel?

Would it not be better to just have 4 x 2.5mm feeding 4 grid switches each on 20A MCB/RCBO then there is no way it can be overloaded? So question is where is the advantage of the ring?

OK post WW2 there was a copper shortage and it all made sense. But with 1/3 rule the ring has become longer than radial so no longer any real point.

 

[plugwash]

Better off to replace the 2.5 with 4....

Maybe, but as I implied in my previous post, although we hear so much about 32A (or 30A) 4mm² radial finals, that's only actually possible if the cable is 'clipped direct' throughout - otherwise one is up to 6mm², which is probably not (or not often) very practical.

mmm, the problem with 6mm² is that even MK sockets are only rated to take two of them. So its ok if your circuit is a pure straight line but if you need to branch for any reason things get messy.

 

[JohnW2]

mmm, the problem with 6mm² is that even MK sockets are only rated to take two of them. So its ok if your circuit is a pure straight line but if you need to branch for any reason things get messy.

That's certainly one problem and another, certainly for mere amateurs, is that I'm sure that trying to play 6mm² within standard backboxes would feel more like plumbing than electrical installation, and a complete pain - 4mm² is bad enough! However, I do wonder how many of these 4mm² radials we hear about really do have their cables 'clipped direct' (or equivalent) throughout their run?

The fact that one can have a 32A ring final in 2.5mm² with installation methods A, 100 or 102, yet would need 6mm² cable for a 32A radial with any of those installation methods is presumably one of the attractions of the ring final?

Kind Regards, John.

 

[ban-all-sheds]

Quite apart from the CCC, the terminal capacity is quite likely to be an issue. As far as I can make out, even for a 32A radial, unless it's all clipped direct, you'd be having to use 6mm² - and for a 40A radial, unless it was all clipped direct, you'd have to use 10mm². I think some sockets (e.g. MK) have terminals rated to take 2 x 6mm², but I don't think any would take 2 x 10mm².

Don't forget that directly buried in a wall is also Ref Method C.

 

[ban-all-sheds]

Are the terminals on sockets OK for 40A ?

A good point, which I'd overlooked when I made that suggestion.

But then according to BS 1363 they only have to be good for 20A.

 

[ban-all-sheds]

Ban, I thought you took a dim view of anyone suggesting a non-standard circuit arrangement...

OK - forget the 40A, revise the Q to "why not use a 32A radial for the kitchen?"

Which is a "standard circuit" despite the apparent anomaly vis-a-vis the required current ratings in BS 1363.....

 

[ban-all-sheds]

That's certainly one problem and another, certainly for mere amateurs, is that I'm sure that trying to play 6mm² within standard backboxes would feel more like plumbing than electrical installation, and a complete pain - 4mm² is bad enough!

Is that necessarily a reason to eschew the design if it's the most appropriate?

Many amateurs would struggle to install SWA, steel conduit or MICC, but that doesn't mean they shouldn't be used if they are a good solution.

 

[stillp]

But then according to BS 1363 they only have to be good for 20A.

Not correct. That's only the current used for the temperature rise test.

I'm getting a feeling we've been here before though.

 

[ericmark]

Although I am sure with mineral or Ali-tube 4mm sq cable we can have a 32A radial Reference Method A it's 33A but in the main it is 20A radials v 32A ring that we look at and instead of maybe 3 rings we can have maybe 5 radials with if required RCBO protection reducing the chance of tripping and if they do trip reducing the area affected.

However I have an issue with multi-RCD as one can trip without it being noticed and supply to fridge and freezer can be lost without one realising.

So question is should one use good quality RCDs like the X-Pole or many RCD's in the form or RCBO's?

 

[ban-all-sheds]

Not correct. That's only the current used for the temperature rise test.

I'm getting a feeling we've been here before though.

Is there anything stopping someone selling a socket which cannot tolerate more than 20A on the cable?

 

[ban-all-sheds]

However I have an issue with multi-RCD as one can trip without it being noticed and supply to fridge and freezer can be lost without one realising.

1) You can have an alarm/alert notifier of some sort.

2) It's possible to install a circuit for F/F that does not need an RCD.

 

[JohnW2]

Don't forget that directly buried in a wall is also Ref Method C.

Indeed. That's why in my most recent post I wrote "'clipped direct' (or equivalent)". However, by no means all wiring is Ref Method C, yet it's the only method which is actually OK for a 32A radial in 4mm².

Kind Regards, John

 

[JohnW2]

That's certainly one problem and another, certainly for mere amateurs, is that I'm sure that trying to play 6mm² within standard backboxes would feel more like plumbing than electrical installation, and a complete pain - 4mm² is bad enough!

Is that necessarily a reason to eschew the design if it's the most appropriate?

No - but I didn't say it was. I do, however, seriously doubt that even a professional would normally contemplate wiring sockets in 6mm² - and, as has already been said, that would limit one to a non-branching radial circuit, because of consderations of terminal capacity (even with MK).

Kind Regards, John.

 

[stillp]

Not correct. That's only the current used for the temperature rise test.

I'm getting a feeling we've been here before though.

Is there anything stopping someone selling a socket which cannot tolerate more than 20A on the cable?

Good question.
There's a general requirement: "Socket-outlets shall be so designed and constructed that in normal use their performance is reliable and without danger to the user or to the surroundings". Given that "normal use" when the standard was written meant in the context of a 30A ring final, I think that would cover it. However BS 1363 doesn't refer to BS 7671 or to the (then) IEE Wiring Regs.

Does anyone sell a socket-outlet limited to use on say a 20A radial?