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18th Edition - Changes to Part 4

05 July 2018

In order to align with the CLC Harmonised Document, the following sentence has been added to the end of Regulation 411.3.1.2 - Protective equipotential bonding:

Metallic pipes entering the building having an insulating section at their point of entry need not be connected to the protective equipotential bonding.

The scope of Regulation 411.3.2.2 has been expanded so that the disconnection times stated in Table 41.1 now apply to final circuits having a rated current not exceeding: 

- 63 A supplying one or more socket-outlets, and

- 32 A supplying only fixed connected current-using equipment.

Previously this requirement applied to all final circuits not exceeding 32 A where the protective measure of automatic disconnection of supply is employed. This change widens the number of circuits covered by Table 41.1 significantly.

Similarly, in Regulation 411.3.3, the scope of the requirement for the provision of additional protection for socket-outlets has been extended from those of rating not exceeding 20 A to 32 A, again broadening the number of cases where this requirement will apply.

An exception to this requirement is still permitted where, other than for an installation in a dwelling, a documented risk assessment determines that RCD protection of such socket-outlets is not necessary. 
However, the previous exception that applied to a specific labelled or otherwise suitably identified socket-outlet provided for connection of a particular item of equipment has been deleted.

To align with the base CLC Harmonised Document, the new Regulation 411.3.4 requires the provision of additional protection by RCD for AC final circuits supplying luminaires within domestic (household) premises.

In the most part, compliance with this is already achieved as a result of the ‘UK only’ requirements for impact protection of cables concealed in walls and partitions and so it will have limited impact on UK practice.

The reference to an operating time of 40 ms at a residual current of 5 IΔn has been removed from Regulation 415.1.1. 

Regulation 411.3.2.5 has been modified significantly and now refers to Section 419 where:

- it is not feasible for an overcurrent protective device to provide automatic disconnection in the event of a fault as required by Regulation 411.3.2, or

- the use of an RCD for this purpose would not be appropriate.  


Regulation 411.3.2.5 also states that disconnection may be required for reasons other than protection against electric shock.

The new Section 419 contains provisions to be applied where it is not feasible that the requirements for automatic disconnection in the event of fault will be met. 

Regulation 419.2 contains measures applicable to where electronic equipment with limited short-circuit current is installed and automatic disconnection is not feasible. It requires that, in the event of a fault between a live conductor and the protective conductor or Earth, for electronic converters of nominal voltage exceeding 50 V AC or 120 V DC, the output voltage of the source is reduced to 50 V AC or 120 V DC or less within the time ordinarily applicable for disconnection.

For all other cases where the requisite disconnection time of Chapter 41 cannot be achieved, Regulation 419.3 requires supplementary protective equipotential bonding is provided so that the voltage between simultaneously accessible exposed-conductive-parts and/or extraneous-conductive-parts does not exceed 50 V AC or 120 V DC.

Regulation 421.1.7 recommends the installation of arc fault detection devices conforming to BS EN 62606 to provide additional protection against fires caused by arc faults in AC final circuits.

All power, control and communication cables – not just low voltage electrical wiring cables - intended for permanent installation in a building or construction must be Construction Products Regulation 2011 (CPR) classified by the 1st July 2017 or they cannot be sold in the UK. Notes to Regulation 422.2.1 and 422.5 refer the reader to item 17 of Appendix 2 in BS 7671 which contains further information on the Construction Products Regulation.

Section 443, dealing with protection against overvoltages of atmospheric origin, has been revised significantly. 

To summarise, such protection is always required where overvoltage affects:

- human life

- public services and cultural heritage

- commercial or industrial activity

- a large number of individuals.

In all other cases a risk assessment is required except:

Where a choice is made to provide overvoltage protection anyway, or

For single dwelling units, where the value of the installation and equipment therein does not justify such protection - NICEIC ands ELECSA advise that any such decision is made only with the full, informed, and documented agreement of the person ordering the work.

Chapter 46 has been reintroduced and contains requirements for provision of isolation and switching, but NOT for the devices used to provide such functions, for which reference should be made to Section 537.

Regulation 463.1.2 states that functional switching devices need not necessarily switch off all live conductors of a circuit. It also permits a single-pole switch for a lighting circuit to be placed in the neutral conductor, albeit acting to energise a control device as shown in Figure 46.1 of BS 7671 and reproduced below. 

Control Circuit

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