Reference Method 100# (above a plasterboard ceiling covered by thermal insulation not exceeding 100 mm in thickness) 4mm is 27A not 30 yes I know surface you can use 4mm but very few houses are wired surface is that an up to date version of OSG?
I never bothered with 17th Edition version was not out when I took C&G2382
When you come to encounter practical situations, however, keep in mind that the "standard" radial circuit limits have changed quite regularly over the years.
The ring specification is not much different from when it was introduced 60 years ago. It's gone from 7/.029 to 2.5 sq. mm. cable, from 1000 sq. ft. to 100 sq. m., from 30A to 32A, and with minor variations in permitted spurs, but they are all relatively small changes.
Radial specifications, on the other hand, have varied quite widely over the years on the floor area and number of sockets.
All right I will agree if you use cable designed to go in stud walls which is rated at 90 deg C and not 70 deg C then you could use 33A (This from 27A for 70 deg cable [2.5 clipped direct] is shown as 33A for 90 deg cable so I would think method 100# where 70 deg cable is 27A the same difference is also true?) but have you tried buying Ali-tube cable? And what do you think are the chances of an apprentice even in collage of being given Ali-tube cable to play with?
I hear other talk about 4mm 32A radials so often and there seems to be no consideration of installation method.
To my mind all 13A sockets should be like the MK type able to take two 6mm cables but that's not the case.
The A1, A2, and A3 seem to be another case of jargon for jargon's sake.
As to unlimited sockets not really 314.1 (iv) means that leakage needs to be taken into consideration and in theory you can exceed the limit with 5 sockets 5 x 3.5ma > 15ma min which 30ma RCD must hold in at. (See 543.7.1.1) so around 20 sockets must be considered as about the max from one 30ma RCD. Yes you could wire in Ali-tube and use RCD sockets and so have as many as you want but in practical terms allowing for some unused sockets and some with appliances with no leakage maybe you could stretch to 30 sockets but can't really say unlimited?
With the move to discharge lights I think soon we will have major problems with houses limited to two RCD's I would prefer to see some figures on number of sockets per 30ma RCD rather than the hit and miss system we have. We need to say "This does not comply" not "This MIGHT not comply"!!!
Shurely it depends on what sort of application the circuit is intended for, in a household a fair few of the items will either be double insulated or have next to no earth leakage hence there isn't a need to look into this in great depth.
If we expect a circuit to be used with high earth leakage appliances then high integrity earthing needs to be employed.
The floor areas for the circuit sizes are also only a rule of thumb, they are not a regulation.
Sorry to butt in at this late stage, but I think lectricians answer is slightly wrong. A1 I believe is the 100sq m max. floor area ring circuit and 32A wlth 2.5mm min. cable and A3 is a radial circuit of max 50sq m floor area and 20A with 2.5mm min. cable.
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