Electrical Fuse box
Of what should be composed a consumer unit in order to comply with latest regulation?
By regulation BS 531.3.2 that emphasize the use of RCD- (Residual protective device) for each circuit, which is a good feature for your house, let’s say for example on the outside light circuit occurs a fault, by having Residual protective device installed in your consumer unit, only the specific circuit that has the fault, will trip and won’t affect the rest of the house as it use to happen with the older version of double RCD protected consumer units.
Obviously consideration should be given to vital circuits as ‘’disabled stair chair’’ ‘’fire alarm’’ ‘’access control’’.
To make a comparison between old Dual protected RCD Consumer Unit and the newest one described above, the Dual RCD protected consumer unit has around 5-8 breakers protected by one main RCD, therefore in the case of a fault occurring down to PE –(protective earth) on one of the circuits, the RCD that protect it and all others circuits under it will trip causing a major disruption of electricity in the house that could affect (lights, main ring, smoke alarm) and with only option to put electricity back on when the fault is been found and fixed.
Of what is composed a consumer unit?
In regulation to comply with latest regulation every consumer should have:
Ref1
‘’Enclosures barriers and fixings
BS 421.1.201 Consumer unit shall have enclosures manufactured from non combustible materials (e.g stell) and comply with BS EN 61439-3.
416.2.1 Basic Protection – Live parts must be inside enclosures and suitable provisions must be made to prevent contact with live parts.
416.2.2 Installed consumer units must achieve IP4X on the top elevation of the enclosure.
416.2.3 Barriers must be secured in place with sufficient stability and durability to achieve and maintain appropriate levels of protection from live parts.
522.8.5 Every cable must be installed to that there is no undue stress or strain on the conductors and terminations (including meter tails) appropriate supports, clips/fixings should be used.
Devices and Components
536.4.203 Only manufacturer approved parts can be used in low voltage assemblies i.e consumer units. Do not mix brands. If in doubt, check with the manufacturer, otherwise the installer becomes the responsible manufacturer.
Additional Protection By 30mA RCD
415.1.1 RCD’s (including RCBOs) with a residual operating current of no more than 30mA are prescribed for provision of additional protection.
411.3.4 Additional protection by use of 30mA RCD shall be provided for all luminaire circuits in domestic household premises.
411.3.3 Additional protection by use of a 30mA RCD shall be provided for all socket outlets up to and including 32 rating.
411.3.3 Additional protection by use of 30mA RCD shall be provided for all mobile equipment for use outdoors up to and including 32A rating.
522.6.203 Cables buried in walls or partitions (which include metallic parts in their construction) shall be provided with additional protection by 30mA RCD, or be installed in earthed metallic, carrier systems that also provide mechanical protection.
701.411.3.3 Additional protection by use of a 30mA RCD, shall be provided for all circuits serving or passing through a location with a fixed bath or shower.
531.1.1 Devices for protection against electric shock must be suitable for isolation as required in Chapter 46 & Section 537.
Protection against unwanted tripping of RCDs & Division of the Installation
314.1 (iv) Every installation shall be divided into circuits as necessary to reduce the possibility of unwanted tripping of RCDs from PE current (not due to a fault).
314.1 (i) Every installation shall be divided into circuits as necessary to avoid danger and inconvenience in the event of a fault.
314.1(iii) Every installation shall be divided into circuits as necessary to take account hazards that may arise from the failure of a single circuit such as a lighting circuit.
531.3.2 RCDs shall be selected and installed so as to limit the risk of unwanted tripping, by either dividing the installation into individual circuits using a 30mA RCBO on each circuit, or by ensuring that PE current is no more than 30% of 30mA.
560.7.1 Circuits of safety services, e.g. fire detection and alarm systems, CO detection and alarm systems, shall be independent of other circuits.
Protection against fires caused by arc faults
131.1.1 The risk of ignition of flammable materials from high temperature or electric arc shall be minimized, there should be minimal risk of burns to people.
421.1.1 Protection against harmful effects from fire caused by electrical equipment is required. Such effects from heat or fire may be caused by failure of equipment or insulation faults, or arcs, sparks and high temperature particles.
421.1.7 AFDDs (arc fault detection devices) are devices that are recommended as a method for providing additional protection against fires caused by arc faults in final AC circuits. Such devices can be used in premises with sleeping accommodation in several other types of location/building
532.6 AFDDs should be installed at the origin of each final (230V AC) circuit that is being protected i.e in the consumer unit.
Safe isolation using main switches/ Protective Devices
462.1.201 A mains switch intended to be operated by ordinary persons must switch both live conductors (L&N) of a single phase supply.
462.2 A means of isolation shall be provided for each circuit, for all live conductors (except as in 461.2) where the neutral is reliably connected to earth by a low resistance and required disconnection times can be met.
422.3.13 Every circuit requires a means of isolation from all live supply conductors. Common isolation of a group of circuits may be provided if service conditions allow.
Protection against overvoltage
443.4 (&5) Overvoltage protection is required in single dwellings where the value of the installation and equipment connected to it justifies the protection.
Identification
514.1.1 A suitable means of identification shall be provided for the identification & purpose of each item of switchgear.’’
Bibliography:
Ref1: 03948-75 Wylex Domestic Installations Poster_v6.indd (wylexreasons.co.uk) 2 January 2021