18th Edition Wiring Regulations

The BS 7671 : 2018 18th Edition IET Wiring Regulations

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Requirements for Additional Protection (30mA RCD)

The 18th Edition Wiring Regulations also has the requirement for additional protection from 30mA RCDs, summarised below.

  1. 421 Protection against fire caused by electrical equipment. 421.1.201
    • Within domestic (household) premises, consumer units and similar switchgear assemblies shall comply with BSEN 61439-3 and shall:

    • Have their enclosure manufactured from non-combustible material, or
    • Be enclosed in a cabinet or enclosure constructed of non-combustible material complying with Regulation 132.12
    • NOTE: Ferrous metal, e.g. Steel, is deemed to be an example of a non-combustible material

  2. 411 Protective Measure: Automatic disconnection of supply(section 411.3.3)

      Additional requirements for socket-outlets and for the supply of mobile equipment for use outdoors

      In AC systems, additional protection by means of an RCD with a rated residual operating current not exceeding 30mA shall be provided for:

    • Socket-outlets with a rated current not exceeding 32A, and
    • Mobile equipment with a rated current not exceeding32A for use outdoors
    • Exceptions are socket outlets under supervision of someone skilled/instructing, and labelled socket, e.g. ‘Freezer’
    • An exception to (i) is permitted where, other than for an installation in a dwelling, a documented risk assessment determines that RCD protection is not necessary

      The requirements of Regulation411.3.3 do not apply to FELV systems according to Regulation411.7 or reduced low voltage systems according to Regulation 411.8

      NOTE 1: See also Regulation 314.1(iv) and 531.3.2 concerning the avoidance of unwanted tripping

      NOTE 2: See Appendix 2, item 11 in respect of risk assessment

      NOTE 3: A lighting distribution unit complying with BS5733, luminaire track system, installation coupler, LSC or DCL is not regarded as a socket-outlet for the purposes of this regulation

  3. 522.6 Impact(section 522.6.201)

      A cable installed under a floor or above a ceiling shall be run in such a position that it is not liable to be damaged by contact with the floor or ceiling or their fixings

      A cable passing through a joist within a floor or ceiling construction or through a ceiling support (e.g. under floorboards), shall:

    • Be installed at least 50mm measured vertically from the top, bottom as appropriate, of the joist or batten, or
    • Comply with Regulation 522.6. All circuits serving or passing through a room with a fixed bath or showerss
  4. Location containing a bath or a shower (section 701.411.3.3)

      Additional protection by the use of one or more RCDs having the characteristics specified in Regulation 415.1.1 shall be provided for low voltage circuits

    • Serving the location
    • Passing through zones 1 and/or 2 not serving the location
    • NOTE: see also Regulations 314.1 (iv) and 531.3.2 concerning the avoidance of unwanted tripping

  5. 341 Division of installation (section 314.1)

      Every installation shall be divided into circuits, as necessary, to:

    • Avoid danger and minimize inconvenience in the event of a fault
    • Facilitate safe inspection, testing and maintenance (see also chapter 46 and section 537)
    • Take account of hazards that may arise from the failure of a single circuit such as a lighting circuitRegted by the failure of other circuits
    • Reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor (PE) currents not due to a fault
    • Mitigate the effects of electromagnetic disturbances (see also chapter 44)
    • Prevent the indirect energizing of a circuit intended to be isolated
  6. 56 Safety Services 560.7.1
    • Except where the recommendations of other safety standards apply, circuits of safety services shall be independent of other circuits

18th Edition BG Consumer Unit Options

Possible consumer unit options to support 18th Edition Wiring Regulations Compliance

Note:- The following diagrams use a 12 module consumer unit to demonstrate the available options

Main Switch

  • Main switch plus the use of RCBOs for every circuit

Split Load

  • Some circuits using MCBs protected by an RCD
  • Other independent circuits using RCBOs
  • Can be created using standard mains switch consumer unit, additional RCD and cable kit CUA5

Dual RCD

  • Some circuits using MCBs protected by an RCD1
  • Some circuits using MCBs protected by an RCD2

High Integrity Dual RCD

  • Some circuits using MCBs protected by an RCD1
  • Some circuits using MCBs protected by an RCD2
  • Other independent circuits using RCBOs

Standard Dual RCD consumer unit offers option of High Integrity Dual RCD as standard
Note: High Integrity Triple RCD is achieved using only the 22 module Consumer Unit

Technical Information


New all metal consumer units comply with 18th Edition Wiring Regulations BS 7671'

Product Standard
Consumer Unit BS EN 61439-3
Main Switch EN/IEC 60947-3
MCB EN/IEC 60898
RCBO EN/IEC 61009-1
Product Standard
RCD EN/IEC 61008
Enclosure EN/IEC 60439
Contactor EN/IEC 60947, 61095
RCBO EN/IEC 61558-1


Devices - Pole pitch 18mm

Consumer Unit Metal(A)
8 modules 244mm
12 modules 316mm
16 modules 388mm
19 modules 442mm
22 modules 496mm


Device Capacity mm2 Max Torque Nm
Switch 35 2.5
MCB 16(32-50A 25mm2) 2
RCD 35 2.5(80A 3.5Nm)
RCBO 16(32-40A 25mm2) 2

*Note 8 & 12 module ‘Tall’ variant, height is 261mm

Cut Outs and Knockouts

Range Top & Bottom Face Sides Base
Metal 8 Module 6 x ø20mm, 1 x ø32mm 1 x ø32mm 1 x ø50 x 100mm
Metal 12 Module 8 x ø20mm, 1 x ø32mm 1 x ø32mm 1 x ø50 x 100mm
Metal 16 Module 9 x ø20mm, 2 x ø32mm 1 x ø32mm 2 x ø50mm, 1 x ø50 x 100mm
Metal 19 Module 11 x ø20mm, 2 x ø32mm 1 x ø32mm 2 x ø50mm, 1 x ø50 x 100mm
Metal 22 Module 13 x ø20mm, 2 x ø32mm 1 x ø32mm 3 x ø50 x 100mm
Insulated 8 Module 4 off - 40, 25 x 16mm 40, 25 x 16mm 3 off - 50, 30 x 40mm
Insulated 12 Module 6 off - 40, 25 x 16mm 40, 25 x 16mm 4 off - 50, 30 x 50mm
Insulated 12 Module Tall 6 off - 40, 25 x 16mm 40, 25 x 16mm, 1 x Ø25 or Ø20mm 4 off - 50, 30 x 50mm
Insulated 16 Module 8 off - 40, 25 x 16mm 40, 25 x 16mm 2 off 50,30 x 50, 4 off 50,30 x 40mm
Insulated 19 Module 9 off - 40, 25 x 16mm 40, 25 x 16mm 6 off - 50, 30 x 50mm
Insulated 22 Module 10 off - 40, 25 x 16mm 40, 25 x 16mm 2 off 50,30 x 50, 6 off 50,30 x 40mm

• Positive contact status indication on Switch, MCB, RCD & RCBO provided by green indicator to show contacts are open

Consumer Unit

  • Max current rating 100A
  • Operating Voltage 230V
  • Short circuit withstand 16kA rms
  • Metal CU base manufactured from
  • 1.2mm steel


  • IP65
  • 5 Module
  • Dims- W-176mm, H- 241mm, D- 100mm
  • Knockouts- Dia ø20mm can be drilled to 32mm, sides - 2 off, top and bottom - 3 off, base - 1 off

Bell Transformer

  • Output voltage 4, 6, 8, 12, 16, 24V
  • Rated output 8VA
  • Consumption 1, 15W


  • Type AC
  • Tripping Time : 1 x In≤100mS, 5 x In≤40mS


  • Type AC
  • Poles: 1 (1P + N)


  • Breaking Capacity 6000A
  • Type B operating 3-5 x In
  • Type C operating 5-10 x In


  • Poles: 2 (1 +N)
  • NO (Normally Open)

Metal Consumer Units

Consumer units for use in domestic household premises

  • Modern stylish design with a profile that matches Nexus wiring accessories
  • Flexibility for maximum circuit combinations, and easy upgrades
  • Fast and simple installation
  • Taller 8 & 12 module consumer unit, with extra space for RCBO’s
  • Consumer unit and devices tested to all relevant standards
  • 10 Year Guarantee
Find out more about Metal Consumer Units
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