I have been told the electrics in the loft have to be on their own
consumer unit. Fine I suppose - except they now say it will be sited
on the ground floor next to the existing CU, which has plenty of spare
capacity. Is it definitely a requirement for a separate CU? Seems
Have you been told on what specific grounds a new one is required? The
only thing I can think of is that there's some something to do with your
scenario which maybe you don't even know about which means it might be
needed? Can't imagine what though.
I don't see how that follows, assuming that the existing circuits on the
CU aren't being modified. The EIC can cover the new circuits only (and
report any observations made on the old). In any case adequacy of the
existing supply, meter tails, earthing and bonding will need to be
checked and if necessary upgraded to ensure compliance of the new work.
Adding a second CU might also require adding a isolator
(switch-disconnector) in order to meet the requirement for a single main
Seems different folk, different tales. Spoke to the BCO and he
confirmed providing the existing CU has the capacity, there is no such
As an aside, 2 smoke detectors run on mains power are required and
must be on a separate circuit. Can each be taken off a different
light circuit or must they be standalone circuits just for the
Either - pros and cons of each. It was discussed here very recently
actually: http://tinyurl.com/3yjg59 (or
The OSG (p56) says they must have battery backup and that supply from a
local, regularly used lighting circuit is OK. (It goes on to say that
they shouldn't be fed via a 30 mA RCD - that'll have to be re-written
Which while not exactly conflicting with the building regs (other than
the "must have battery backup" bit), only covers one of the options they
1.17 The power supply for a smoke alarm system should be derived from
the dwelling's mains electricity supply. The mains supply to the smoke
alarm(s) should comprise a single independent circuit at the dwellings
main distribution board (consumer unit). If the smoke alarm installation
does not include a stand-by power supply, no other electrical equipment
should be connected to this circuit (apart from a dedicated monitoring
device installed to indicate failure of the mains supply to the smoke
alarms - see below).
1.18 A smoke alarm, or smoke alarm system, that includes a standby
power supply or supplies, can operate during mains failure. It can
therefore be connected to a regularly-used local lighting circuit. This
has the advantage that the circuit is unlikely to be disconnected for
any prolonged period. "
Thanks for all that (which I see is reproduced in the EGBR).
B1-1.20 (2000 version) and the EGBR says that the non-use of an RCD is
only "preferable" and that any RCD should not also protect sockets for
outdoor portable equipment. All quite sensible and an obvious case for
an RCBO in a TT system or in 17th edition land.
B1-1.20 (2006 version) just says that the electrical installation should
comply with Approved Doc. P, which is about as vague as it comes. In
fact the 2006 version of AD-P refers you back to the 2000 version of B1
- what a mess.
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