New UK electrical wiring regulations for medical and dental centres

28 October 2011

Background to the new regulations

The amended Wiring Regulations, BS 7671:2008(2011) is based on CENELEC HDs and IEC standards, ie those of Europe and of the international community.

The standardisation process is perpetual and standards are continually evolving requiring national standards bodies to incorporate the technical changes. Therefore, the amended Wiring Regulations embody the most recent changes made at a European and International level.

One of the major changes, which those working within medical locations should familiarise themselves with, is Section 710 which sets out requirements for electrical installations in hospitals, private clinics, medical and dental practices, healthcare centres and dedicated medical rooms in the work place.

In addition, a number of new sections have been added which are also relevant. These relate to electromagnetic disturbances, devices for protection against overvoltage, and operating and maintenance gangways. This article outlines these key changes.

Section 710 — Medical Locations

Electrical equipment based in medical locations presents particular risks to patients. Section 710 therefore sets out stringent measures which are necessary to ensure the safety of patients likely to be subjected to the application of electrical medical equipment.

The human body's natural protection against electric shock is considerably reduced when certain clinical procedures are being performed on it. Surgical or clinical invasive procedures bypass the skin's resistance when applied parts are being used inside the body.

One of the main measures introduced by Section 710 is in the division of medical rooms in to 3 different groups depending upon the type of treatment they deliver and the potential hazards of electrical shock to patients. The 3 different groups are:

• Group 0 — Medical locations where no applied parts are intended to be used and where discontinuity (failure) of the supply cannot cause danger to life.
• Group 1 — Medical locations where discontinuity of the electrical supply does not represent a threat to the safety of the patient and applied parts are intended to be used as follows: externally — invasively to any part of the body, except where 710.3.7 applies.
• Group 2 — Medical locations where applied parts are intended to be used in applications such as intracardiac procedures, vital treatments and surgical operations where discontinuity (failure) of the supply can cause danger to life.

To protect patients from possible electrical hazards, Section 710 sets out other additional protective measures to be adhered to. These include: particular requirements for protection against electric shock; medical IT systems — requirements concerning supplementary equipotential bonding; additional requirements for the selection and erection of electrical equipment including switchgear and controlgear; and safety services including the sources and detailed requirements for safety lighting.

Section 444 — Electromagnetic disturbances

This is an entirely new section brought about by developments in CENELEC — HD 60364-4-444 Measures against electromagnetic disturbances. In 1996, the EMC Directive (89/336/EEC) was issued requiring electromagnetic compatibility of products being sold across Europe. The Directive relies on harmonised standards to which products are to comply; the CE mark, for example, is a direct result of the work undertaken to remove trade barriers and, hence, allowed development of the EMC Directive. In 2004, the EMC Directive was modified as 2004/108/EC and came into force in July 2007; the main change was the inclusion of fixed installations.

Therefore, Section 444 has been developed to provide the basic requirements and recommendations to enable the avoidance and reduction of electromagnetic disturbances and meet the Directive. The section includes guidance for the location and sources of electromagnetic disturbances relative to the positioning of other equipment as well as measures for minimising electromagnetic disturbances.

Section 534 — Devices for protection from over voltage
This is a new section which has been implemented by CENELEC in HD 60364-5-53. A surge protective device (SPD) is a device that is intended to limit transient overvoltages and divert damaging surge current away from sensitive equipment. Equipment is now more precise with little tolerance on the components, hence, less robust than it ever was, making SPDs more important than ever.

SPDs must have the necessary capability to deal with the current levels and durations involved in the surges to be expected at their point of installation. SPDs can operate in one of two ways, based on the component technologies within them.

One way is as a voltage switching device where under normal conditions, the device is an open circuit, but at a certain threshold voltage the SPD conducts and diverts the current through it. It has two states, ON and OFF, hence the name of voltage switching.
Another way is as a voltage limiting device. Voltage limiting SPDs again present an open circuit under normal circuit conditions. When an overvoltage is detected the device begins to conduct, dropping its resistance dramatically such that the overvoltage is limited and the surge current is diverted away from the protected equipment.

Section 534 gives detailed requirements on the selection, connection, installation and co-ordination of Surge Protection Devices.

Section 729 — Operating and maintenance gangways

Section 729 is intended to ensure a safe working environment for skilled or instructed persons working in areas such as switchrooms and controlgear assemblies where, historically, not much space has been allocated. The Section has been incorporated into Amendment Number 1 in order to align with the European Harmonised Document. Regulation 15 of the Electricity at Work Regulations requires that adequate working space, means of access and lighting shall be provided at all electrical equipment on which, or near which, work is being done.

The Section sets out minimum requirements for the provision of adequate working space, means of operational and emergency access and evacuation at, or near, electrical equipment which is being worked on. The amended Regulations outline new requirements that the width of gangways and access areas shall be adequate for work, operational access, emergency access, emergency evacuation and for the movement of equipment.

For more information

If you have any questions about the IET Wiring Regulations, 17th Edition, BS 7671:2008 incorporating Amendment No 1: 2011 you can call the free Technical Helpline to speak to an expert at the IET on 01438 765599 or email: technical (at) theiet.org

You can purchase the new Wiring Regulations here www.theiet.org/amend1. As the authority on the requirements for electrical installations, the IET also offers a series of Guidance Notes which you can find out more about here: www.theiet.org/electrical.