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TECHN I CAL DATA
1 7 t h ED I T I ON COMP L I ANCE
MAINS SUPPLIES FOR SMOKE ALARMS
WITHIN DOMESTIC SETTINGS
Clause 7.1 of BS 5839-6 defines a Grade D system
as: “A system
of one or more mains-powered smoke alarms, each with an integral
standby supply (The system may in addition, incorporate one or more
mains-powered heat alarms each with an integral standby supply).
The 17th Edition of the wiring regulations do not cover every item of
Electrical Equipment likely to be installed. They do not specifically
mention Smoke Alarms. However:
CHAPTER 13 REGULATION 134.1.1
states that electrical equipment
shall be installed in accordance with the instructions of the
manufacturer of the equipment.
CHAPTER 51 REGULATION 510.2
states that every item of electrical
equipment shall be selected and erected so as to allow compliance
with the regulations stated in this chapter and the relevant regulations
in other parts of BS7671 and shall take account of manufacturers
instructions.
Elements of Electrical Protection will include short circuit, overcurrent
and may also include additional protection by a residual current device
(30mA) for certain installation methods covered by BS7671 (522.6.7)
& (522.6.8)
IF ADDITIONAL PROTECTION IS REQUIRED BY BS7671 THE NEED
FOR SEPARATE ELECTRICAL PROTECTION CANNOT BE MET BY
DUAL RCD CONSUMER UNIT ARRANGEMENTS WHERE SINGLE
RESIDUAL CURRENT DEVICES PROTECT GROUPS OF CIRCUITS.
REQUIREMENTS FOR ELECTRICAL INSTALLATIONS.
l
SOCKET CIRCUITS 411.3.3
RCDs are now required to provide additional protection. To be recognised
as providing additional protection the RCD must be rated at 30mA or less
and operate within 40ms when tested at 5x rated residual operating current.
RCDs are now required for all general use socket outlets
rated up to 20A.
Two exceptions are allowed for ;
1.
Socket outlets used under supervision of skilled or instructed persons.
2.
A socket outlet suitably identified for connection of a particular
item of equipment.
Additional protection must be provided in the event of failure of the
provision of basic protection and/or the provision of fault protection or
carelessness by users of the installation.
Protection by 30mA RCD will
be required for;
Upstairs ring circuit
Downstairs ring circuit
Kitchen ring circuit
Cooker control unit c/w socket outlet
CABLES 522.6.6 522.6.7 522.6.8
Regulation 522.6.6
A cable concealed in a wall or partition at less than 50mm from the
surface shall;
1.
Incorporate an earthed metallic covering suitable for service as the
circuit CPC -
or
2.
Be enclosed in earthed conduit
or
3.
Be enclosed in trunking or ducting
or
4.
Be mechanically protected against damage from penetration by nails
or screws and the like
or
5.
Be installed in the prescribed zones.
Regulation 522.6.7
Where 522.6.6 applies and the installation is
not
intended to be under the supervision of skilled or instructed
persons,
cables installed in accordance with 522.6.6(5) but not having
mechanical protection of 1,2,3 or 4 shall be provided with additional
protection by means of a 30mA RCD.
In the majority of domestic situations cables installed beneath a plaster
surface within partition walls without mechanical protection will require
additional protection by
30mA RCD regardless
of their routing.
Upstairs lighting
Downstairs lighting
Immersion heater
Smoke alarm
Burglar alarm
Bathrooms
Section 7
Special installations or Locations.
Section 701
Locations containing a bath or shower.
Zone 3 has been removed.
Suitable equipment can be within 600mm of a bath, excluding 13A
sockets to BS1363 which must be 3m from the edge of a bath or
shower.
Additional protection shall be provided by the use of
one or more
residual current device
with a rated operating current not
exceeding 30mA (701.411.3.3).
Supplementary bonding is not required so long as any Protective
Equipotential Bonding has been installed (411.3.1.2).
Additional protection must be provided by one or more 30mA RCDs.
shower circuit
lighting circuit
Heating circuit
Ventilation circuit
Chapter 31
314.1 Requires that; Every installation shall be divided into circuits,
as necessary, to:
i.
Avoid danger and minimise inconvenience in the event of a fault
ii.
Facilitate safe inspection, testing and maintenance
iii.
Take account of danger that may arise from the failure of a single
circuit such as a lighting circuit
iv.
Reduce the possibility of unwanted tripping of residual current
devices (RCDs) due to excessive protection conductor currents
produced by equipment in normal operation.
British Standards and IEE regulations are subject to change and
amendment. This guide to Crabtree consumer units is not a
substitute for the regulations which should always be used for
all types of electrical installation design, and installation work.
Manufacturers
Instructions
BS7671
BS5839-6
Installation shall be in
accordance with
BS 7671 & BS5839-6
522.6.7
522.6.8
560.7.1
cable installation
method
Clause 15.5 states that
Grade D systems can be
wired from either:
A. An independent
circuit at the dwellings
main distribution board.
B. A separately
electrically protected
regularly used lighting
circuit.
Main
Switch
RCD
MCB
MCB
MCB
MCB
MCB
MCB
RCD
SD
SD
MCB or RCBO
MCB or RCBO
Main
Switch
RCD
MCB or RCBO
MCB or RCBO
MCB
MCB
MCB
MCB
MCB
MCB
RCD
SD
SD
SD
A.
B.