Ring and Radial
- Thread starter Blimey
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There is no real reason these days for having any ring circuits.
They were introduced to allow smaller cable to be used with 30A rewireable fuses - (metric equivalent 2.5mm² instead of 6mm²)
With MCBs this does not apply.
The layout (if, for example, the accessories actually go all the way round the kitchen from near the CU) may make a ring advantageous.
Edit - inserted accessories instead of circuit
They were introduced to allow smaller cable to be used with 30A rewireable fuses - (metric equivalent 2.5mm² instead of 6mm²)
With MCBs this does not apply.
The layout (if, for example, the accessories actually go all the way round the kitchen from near the CU) may make a ring advantageous.
Edit - inserted accessories instead of circuit
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Whilst I'm no champion of ring circuits, it obviously remains the case that smaller cable (2.5mm²) can usually be used for a ring final protected by a 32A MCB than would be required for a radial circuit protected by a 32A MCB. Whether that is sufficient reason for using a ring is a different question!
Ring finals also offer the advantage of CPC redundancy, but that may or may not be outweighed by the risk of the L or N ring being (unknowingly) broken, with the consequent risk of cable overloading.
Kind Regards, John
Yes, but a radial with 30A BS3036 would require a cable with >41A CCC - as opposed to 4mm² (<2x2.5) with 32A MCB.
So they devised the 30A 3036 ring.
So they devised the 30A 3036 ring.
I never quite see the validity of that argument when it applies to no other circuit.
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It must be 15 years since I last installed a ring from scratch, radials every time for me
@EFLImpudence @JohnW2 Thanks for the quick replies. The radial circuit (2.5mm² with 20A fuse) downstairs will have six sockets and a fused connection to the boiler. It's an old consumer unit at present that will be replaced.
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You mean just "radial" ?
I don't quite understand your point. Ring finals and (some) circuits with explicit 'high integrity earthing' are the only ones which have this feature - which, in itself, enhances safety. So, yes, that 'safety feature' does not exist in relation to any other types of circuit - but that doesn't alter the fact that, in those two situations, it does (in that one respect) enhance safety.
Kind Regards, John
My point is that CPC redundancy is not a consideration when installing circuits.
That a ring has this this 'advantage' is countered by, as you say, the same thing occurring to the live conductors.
You are always free to fit 'HI earthing' should you wish but we don't.
That a ring has this this 'advantage' is countered by, as you say, the same thing occurring to the live conductors.
You are always free to fit 'HI earthing' should you wish but we don't.
@EFLImpudence (should have said circuit not ring) yes, only the radial circuit on 20A
I do not know if it is true, but stillp is always telling us that it was a significant consideration in relation to the introduction of ring finals.
Kind Regards, John
Neither do I. It doesn't really make sense.
Perhaps it was a persuasive tool for those who weren't to keen.
In the absence of downsides, CPC redundancy obviously makes sense (just as does the {I presume} dual braking system you have in your car). As for the downsides, given the 'margins' we often discuss, and given how unlikely it is that both L and N rings would be broken simultaneously (unless by human act!), I don't think there is really an appreciable risk of 20A CCC cable being 'seriously overloaded'. Of course, if (as commonly) the CCC is 27A, I would say that the chances of a 'serious overload' are then virtually non-existent.
Do I take it that, unless explicitly asked to by a customer, you would not install a ring final new circuit?
Kind Regards, John
Well, I have retired but -
I would not - unless the route was very favourable - as above.
If you are now going to argue for ring finals wherever possible, for that reason, then perhaps we could have T&T (Twin & Two earth, instead of T&E) for radial circuits.
Fair enough.
As I said, I'm no champion of ring finals - so, no, I would not argue that. However, what I would argue is that IF one would feel more comfortable with CPC redundancy, then one should implement it, one way or another (but should also take into consideration any downsides of the method of implementation one chooses).
As for those downsides, I would be interested to know how often (if ever) electricians have come across a ring final cable which has come to any significant harm (or posed a significant hazard) as a result of a break in the ring..
Kind Regards, John