Tuesday, 6 November 2012


Persons involved in electrical installation work must be competent,competent, competent.
The Electricity at Work Regulations 1989 imposes duties on persons involved in
electrical work commercially, whether employers, the self-employed or
employees, including most trainees.
Regulation 16 (Persons to be competent to prevent danger and injury) states: “No person shall be
engaged in any work activity where technical knowledge or experience is necessary to prevent danger or, where appropriate, injury, unless he possesses such knowledge or experience, or is under such degree of supervision as may be appropriate having regard to the nature of the work.”
The Memorandum of guidance on the Electricity at Work Regulations 1989 (HSR25, HSE: 1989) states that: “the object of the regulation is to ensure that persons are not placed at risk due to a
lack of skills on the part of themselves or others in dealing with electrical equipment”.
It continues:
“the scope of ‘technical knowledge or experience’ may include:
(a) adequate knowledge of electricity;
(b) adequate experience of electrical work;
(c) adequate understanding of the system to be worked on and practical experience of that class of system;
(d) understanding of the hazards which may arise during the work and the precautions which need to be taken;
(e) ability to recognise at all times whether it is safe for work to continue.”

Construction sites are potentially dangerous in many ways. Four factors contribute to the high risk of electric shock on a construction site:
1 the possibility of damage to cables and equipment.
2 the widespread use of hand tools with trailing leads (this problem
is mitigated by the increasing use of battery operated tools).
3 the accessibility of many extraneous-conductive parts, which cannot practically be bonded.
4 the works are generally open to the elements.
Section 704 of Amendment 1 of BS 7671:2008 prescribes particular measures to reduce the risks caused by this harsh environment. For example:
BS 7671 strongly prefers the reduced low voltage system to supply portable hand lamps for general use and portable hand tools and local lighting up to 2kW, while SELV is strongly preferred for portable hand lamps in confined or damp locations.
It is usually impracticable to comply with the bonding requirements of the Electricity Safety, Quality and Continuity Regulations on construction sites for PME. Hence BS 7671:2008(2011) states
that a PME earthing facility shall not be used for the means of earthing for a construction site installation unless all extraneous-conductive-parts are reliably connected to the main earthing
terminal. See Regulation 704.411.3.1 Section 704 prohibits the protective measures of obstacles and placing out of reach (Section 417), non-conducting location (Regulation 418.1), and earthfree
local equipotential bonding (Regulation 418.2).
Cables on a construction site location should preferably not be installed across walkways or site roads as they are susceptible to mechanical damage.
If cables are installed in this manner they require the appropriate level of mechanical protection.
For reduced low-voltage systems flexible thermoplastic cables rated at 300/500V and suitable for low
temperature (BS 7919) should be used. These cables remain flexible at lower temperatures than standard PVC cables, and are ideal for outdoor use. They are referred to as arcticgrade cable and typically have yellow (refer to section 4.6 of IET Guidance note 7) or blue sheaths.
For cables used for applications exceeding reduced low voltage, flexible cables rated at 450/750V that are resistant to abrasion and water should be used, type H07RN-F (BS EN 50525
part 2.21). (Please note, whilst BS7019 is still current, it is expected to be
withdrawn end of December 2012).
These are heavy duty rubber insulated and sheathed flexible cables suitable for outdoor use.
All equipment that is part of the movable installation should have a degree of protection appropriate to the external influences. Equipment for external use should be at least IP44.
However, equipment installed in aweather protected location, such as an office being refurbished, should be at least IP 2X (see BS 7671 for exact requirements).
It is recommended that the maximum period between inspections of construction site installations is three months.
Fixed installation RCDs should additionally be tested daily (using the integral test button). Should RCDs be used as supplementary protection to protect mobile equipment they must be tested by the operative before each period of use (again using the integral test button) and by the responsible
person every three months (using anRCD tester). *

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