The 17th Edition requires socket-outlets rated at up to 20 A and intended for use by ordinary persons to be provided with additional protection by means of a 30 mA RCD. Many socket-outlets in offices may be considered to be subject to this requirement. However, many offices will have computers producing protective conductor current, individually and/or collectively. This accumulated protective conductor current could cause the circuit RCD to operate. Such disruption will not be acceptable to the office users, particularly in banks etc. How can such unwanted tripping be avoided?

Where additional protection by RCD is necessary, unwanted tripping can be avoided by appropriate sub-division of circuits.

Which 13 A socket-outlets in commercial and industrial premises are required to have additional protection by RCD?

Socket-outlets in commercial and industrial premises must have additional protection by means of an RCD if they are rated at 20 A or less and are for general use without the supervision of a skilled or instructed person.  An exception is made for a specific labelled/identified socket-outlet for a particular item of equipment.

The decision as to which socket-outlets are provided with RCD protection in accordance with these criteria should be made in consultation with the client’s duty holder under the Electricity at Work Regulations 1989.

Which socket-outlets in commercial and industrial premises are NOT required to have additional protection by RCD?

Socket-outlets in commercial and industrial premises must have additional protection by means of an RCD if they are rated at 20 A or less and are for general use without the supervision of a skilled or instructed person.  An exception is made for a specific labelled/identified socket-outlet for a particular item of equipment.

The decision as to which socket-outlets are provided with RCD protection in accordance with these criteria should be made in consultation with the client’s duty holder under the Electricity at Work Regulations 1989.

As a general principle, it may be considered that socket-outlets in commercial and industrial premises NOT needing to have additional protection by means of an RCD include the following: a socket-outlet labelled for the connection of a specific item of equipment; socket-outlets not intended for general use, such as those in floor service boxes intended for the connection of workstations and other IT equipment; socket-outlets for use under the supervision of skilled or instructed persons so as to minimize the possibility of careless use.

How do I decide what grade and/or type of fire alarm and emergency lighting systems should be provided for a commercial property?

Reference should be to the applicable Building Regulations, BS 5839-1 and BS 5266 which give specific recommendations.

If an RCD is used to achieve automatic disconnection within the prescribed time, is the supplementary bonding called for in 411.3.2.6 still required?

No. An RCD is a valid way of complying with automatic disconnection requirements.

In a milking parlour, is supplementary bonding required only where livestock can make simultaneous contact with extraneous-conductive parts (such as metallic gate posts and gates) and exposed-conductive-parts?

No. The 17th Edition requires all extraneous- and exposed-conductive-parts that can be touched by livestock to be supplementary bonded, whether or not the parts are simultaneously accessible.

Does a portacabin that is intended to be moved from place to place only infrequently, and which is supplied for example by SWA cable, fall within the scope of Section 717 of the 17th Edition?

No. Section 717 applies to transportable units that are intended to be moved relatively frequently from place to place and which therefore need to be supplied through flexible cables.

Where automatic disconnection to Regulation 411.3.2.1 cannot be achieved in the prescribed time and supplementary bonding is be provided in accordance with Regulation 415.2, where should the supplementary bonding be located?

At the location of the equipment which cannot be disconnected in the prescribed time. Consideration must be given to disconnection required for reasons other than electric shock, for example, overcurrent protection.

Where automatic disconnection to Regulation 411.3.2.1 cannot be achieved in the prescribed time and supplementary bonding in accordance with Regulation 415.2 cannot be provided because there are no simultaneously accessible exposed-conductive-parts and extraneous-conductive-parts, (including flooring) is shock compliance achieved?

Yes.