This article is the second part of two that looks at summarising protective measures applied to special installations or locations defined in Part 7 of the 17th Edition of the IEE wiring Regulations (BS 7671:2008). In particular, this article looks at Sections 712 to 753.
One of the fundamental principles for electrical installations is protection for safety (Section 131) in which Regulation 131.2 Protection against electric shock requires protection to prevent a person or livestock coming into contact with live parts by the provision of basic protection (direct contact) as well as fault protection (indirect contact) to prevent an electric shock when an exposed conductive part becomes live due to a fault. The technical requirements of this principle are dealt with in Part 4 of the Regulations by Chapter 41 “Protection Against Electric Shock”. This chapter highlights four protective
measures that are generally permitted (Regulation 410.3.3);
- Automatic disconnection of supply (Section 411)
- Double or reinforced insulation (Section 412)
- Electrical separation for the supply to one item of current using equipment (Section 413)
- Extra –low voltage SELV and PELV (Section 414)
The application of one or more of these protective measures in an installation needs to take into account the external influence. Section 415 also gives requirements to provide
additional protection by the provision of a residual current device (RCD) and supplementary equipotential bonding for certain conditions, including special installations or locations. For special installations or locations there are particular requirements for each Section that either supplement or modify the requirements of the protective measures defined in Chapter 41. Table 1 overleaf summarises the application of the above protective measures
for the listed special installations or locations, highlighting the specific supplementary or modified requirements for a protective measure. In certain instances there are additional general requirements as well as additional protection (Section 415) requirements which
enhance the protective measures.
In addition to the general protective measures already highlighted there is the protective measure of obstacles and placing out of reach (Section 417). It is worth highlighting that this is a protective measure that only provides basic protection and would only be applicable in installations that are restricted to skilled or instructed persons under the supervision of skilled persons.
To view the full article and Tables from the IET's Wiring Matters Summer 2009, click on the attachment below...