Ring main.

K

kai

Is it the case, if you have a ring main, with all sockets protected by a 30ma RCD at the mains supply in the CU, you can NOT run off a fused spur from the ring, into the Garden, feeding a MK masterseal double socket, if the total floor area including the garden exceeds 100 square metres?

A lot of books seem to still say that you can run a fused spur into the Garden, as long as the circuit has 30ma RCD protection on.
 
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kai said:
Is it the case, if you have a ring main, with all sockets protected by a 30ma RCD at the mains supply in the CU, you can NOT run off a fused spur from the ring, into the Garden, feeding a MK masterseal double socket, if the total floor area including the garden exceeds 100 square metres?

A lot of books seem to still say that you can run a fused spur into the Garden, as long as the circuit has 30ma RCD protection on.

ive never herd of that 1 before. i think its allowed, since you cant define the outside area. or you could just plug in an extension lead and take that outside. has the same effect
 
kai said:
Is it the case, if you have a ring main, with all sockets protected by a 30ma RCD at the mains supply in the CU, you can NOT run off a fused spur from the ring, into the Garden, feeding a MK masterseal double socket, if the total floor area including the garden exceeds 100 square metres?

A lot of books seem to still say that you can run a fused spur into the Garden, as long as the circuit has 30ma RCD protection on.

The 100m² is a rule of thumb which, in most cases, will allow you to install a ring final circuit with as many sockets as you like without using an excessive length of cable which might lead to either/or excessive volt drop or insufficiently low earth fault loop impedance. You can then spur off as many of these sockets as you like with no restriction in the length of those spurs except common sense and the usual consideration of volt drop/Zs - nowhere is it stated that you have to include the area of your garden in the 100m².

The use of RCD for supplementary protection against direct and/or indirect contact has nothing whatsoever to do with the size of your garden, house, driveway, distance to the nearest post office, or anything else.
 
Surely it's a bit more than a rule of thumb. More like written down somewhere. Though I would have to agree that including the total area of the garden would be a bit of a nonsense.

I have the idea it says something like 'the area served must not be more than 100sq m'. Which, worded like that, would indeed suggest including your entire 1000 sq m garden.
 
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On Site Guide, page 151, snappily titled: Final Circuits using socket-outlets complying with BS1363-2 and fused connection units complying with BS 1363-4

A ring or radial circuit, with spurs if any, feeds permanently connected equipment and an unlimited number of socket-outlets and fused connection units.

The floor area served by the circuit is determined by the known or estimated load and does not exceed the value given in Table 8A.

A single 30A or 32A ring circuit may serve a floor area of up to 100m²...
[some stuff about washine machines]...

Diversity between socket-outlets and permanently connected equipment has already been taken into account in Table 8A and no further diversity shoule be applied.


The garden area is nothing to do with the calculation, as the floor area in question is expected to be contained within the equipotential zone of the building.

The application of diversity involves a certain amount of educated guesswork, because no designer can fully anticipate what load may be applied to a socket-outlet circuit in the future. Table 8A summarises how that educated guesswork can be applied. By one definition I found, a rule of thumb is an "easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination." I think that covers it nicely.
 

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