I don't mind a ring final circuit but diyers dont know how to add to them properly....anyone (ish) can add to a radial circuit
Advice - First Fix Ring main or Radial?
- Thread starter bilabonic
- Start date
So people don't use 4mm² because it is dearer because people don't use it.
How could that be overcome?
How could that be overcome?
Indeed - but if one was only installing 32A Method C radials, one would only need to buy 4mm² cable. As I've said before, if the only possible installation methods would require 6mm for a radial, I probably would revert to a ring, since (unlike 4mm²), 6mm² T+E is not so easy to use with (and a problem to get three dictators into a terminal for branches).
It obviously depends upon the topology of the circuit, but the cable for a 4mm² radial will often cost much the same as, and sometimes less than, that for a 2.5mm² ring. Current TLC prices (excluding VAT) are £40 for a 50m reel of 2.5mm and £35.25 for a 25m reel of 4mm. Hence, in the simplest hypothetical case of sockets arranged in a straight line radiating from the CU, with the furthest socket 25m from CU, it would cost about 13% more (in cable) to have a 2.5mm² ring than a 4mm² radial.
Good question - but maybe almost moot - since, as I've just written, using 4mm² (radials) is not necessarily 'dearer'.
A valid point - but I'm not convinced that DIYers with the degree of knowledge you're talking about would necessarily always use the correct size cable when 'adding to' a 32A radial!
There is a 'saving grace', although I suppose I shouldn't mention it - since it flies flagrantly in the face of the regs! .... I would suggest that the reality is that it is exceedingly unlikley that a domestic 32A radial wired (in part or all) with 2.5mm² would ever result in any problems - given that it would be very rare that such a circuit would ever be asked to carry more than 27A (or, probably, more than 20A or so) in total for appreciable periods of time!
Yeah I think 2.5mm takes 32 amp easy, don't tell anyone I said that.
If the furthest socket is 25m away for the CU then I think that is a big old house rather than a normal/modern house.
I won't
... but you're in good company, since even BS7671 effectively acknowledges that (if installed Method C) it can safely carry over 39A for an hour (and higher currents for shorter periods)!
We're obviously talking about 25m (or whatever) 'as the cable flies', which (even in a 'normal/modern' house) can sometimes equate to a much shorter distance from the distance 'as the moth (or even human) flies' (see **) - but I'm pleased to see you saying that, and I hope you might remind people of it next time eric start talking about 'maximum circuit lengths' of 106m (or even 32m)
[ In the room of a house (e.g. a modern bungalow) in which there are, say, 6 sockets each on, say, 1.5m drops from above the ceiling, the cable length could well be 20m-25m just for that one room ]
If you also promise not to tell anyone I said this .... in the context of a domestic 32A radial, I might possibly even have said something similar about 1.5mm² (and maybe even 1.0mm²) cable, for the same reasons
A catch is, of course, that the maximum Zs for adequate fault protection, remains 1.37Ω with a B32, regardless of the cable size. Assuming Method C and a TN-S Ze of about 0.6Ω (say about 0.8Ω maximum R1+R2), that equates to a maximum (radial circuit) cable length of only about 34m for 2.5/1.5mm² T+E, about 22m for 1.5/1.0 mm² T+E and about 18m for 1.0/1.0 mm² T+E !!
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