NAPIT’s Don Holmes offers clarification and advice for contractors.
Every year, the use of electricity on construction sites results in accidents from electric shock and burns which can be serious or even fatal.
This article will consider the various regulations and requirements applicable to temporary electrical installations in construction and demolition sites.
The Health and Safety at Work etc. Act 1974 (HSAWA)
The HSAWA places a duty on every employer to ensure so far as is reasonably practical, the safety and welfare at work of all employees.
The Management of Health and Safety at Work Regulations 1999 (as amended)
These regulations place a requirement on every employer to assess every work activity in order to identify any hazard that employees or any other person might encounter as a result of the work being carried out.
HSE document INDG 163 gives advice on these regulations.
The Provision and Use of work Equipment Regulations 1998 (as amended)
All electrically- operated power tools are covered by these regulations.
HSE Approved Code of Practice L22, Safe use of work equipment, contains advice which has legal status.
The Electricity at Work Regulations 1989 (EAWR)
The EAWR apply to all situations involving electricity at any place of work. They place legal obligations on both employers and employees.
Guidance can be found in, Electricity at Work Regulations 1989, Guidance on Regulations (HSR25)
Requirements for Electrical Installations BS 7671:2018
Section 704 of BS 7671 contains requirements for construction and demolition site installations.
The Construction (Design and Management) Regulation 2015 (CDM)
The CDM regulations apply to all building and construction work and include new build, demolition, refurbishment, extensions, repairs and maintenance.
HSE publication L153 contains guidance on the CDM Regulations.
Electrical contractors starting work on a site
Site requirements must have a site-specific induction informing persons of the particular risks associated with the site and the arrangements made to control those risks. The detail provided will be determined by the risks involved.
Construction site facilities and equipment requiring an electrical supply
On a typical construction site for the construction of blocks of flats, the facilities and equipment requiring a temporary electrical supply include:
Three-phase
400 Volts
Tower crane. Fig 1
Batching plant. Fig 2
Fig 3
Single-phase
230 Volts
Welfare facilities.
Personnel security gate. Fig 4
Exterior floodlighting. Fig 5
Reduced Low Voltage (RLV) 110 V
Socket-outlets and site lighting.
50 V
Portable hand lamps.
25 V
Portable hand lamps for use in confined or damp situations.
Where an RCD protects a tower crane supply, it will need to have appropriate trip current and time-delay settings to avoid unwanted tripping and to achieve selectivity (discrimination) between RCDs.
Temporary Electrical Supply
Temporary supplies for construction sites often present challenges when the power requirements are estimated.
Provision needs be made for temporary supply cables to be terminated in a safe, secure and robust way. BS 7671 states that a PME facility shall not be used for a means of earthing unless all extraneous-conductive-parts are reliably connected to the main earthing terminal.
Since most electricity suppliers will not guarantee the integrity of the supply Earth, they will usually provide construction sites with a TT supply, which requires an RCD to protect the overall installation. Regulation 704.411.3.2.1 of BS 7671 states that an RCD with a rated residual operating current not exceeding 500 mA must be used.
Generators
As an alternative to a temporary electrical supply from an electricity supplier, or to supplement the supply, portable generator(s) may be used (Fig. 6). The manufacturer’s instructions must be followed.
Electrical site distribution equipment
All units for the distribution of electricity are to comply with BS 4363 Specification for distribution assemblies for RLV supplies on construction and building sites. Socket-outlets to BS EN 60309-2 are designed to prevent plugs designed for one voltage being connected to socket-outlets of another voltage. This is achieved by different positions of the keyway in the plug and socket-outlet.
Plugs, socket-outlets and cable couplers are colour- coded to identify the rated voltage (Table 1).
A typical range of site distribution equipment is illustrated in Fig 7.
Supply incoming unit (SIU)
Mains distribution unit (MDU)
Transformer unit (TU) a TU 1 unit for single-phase 230 /110 V.TU3 for three-phase 415 / 110 V.
Outlet unit (OU) for 110 V 16 A or 32 A socket-outlets.
Extension outlet units (EOU) for 110 V 16 A socket-outlets.
Cables
Cables should be installed in ducts below ground level, typically 0.5 metres. A record of the location should be recorded using maps or plans showing route and depth. Alternatively, a suitably protected overhead cable can be run at a suitable height.
All distribution cables which carry 400 V or 230 V on a construction site must have a metal sheath or armour which is effectively earthed.
Lighting
In order that work can continue effectively and safely in periods of insufficient natural light, suitable internal and external artificial lighting must be installed. The Clean Neighbourhoods and Environment Act allows Local Authorities to undertake action when external light emitted from premises is prejudicial to health or is a nuisance.
Testing and inspection
Table 3 of IET Guidance Note 3 Inspection and Testing, recommends that construction site installations should be inspected and tested every 3 months.
Portable tools used by contractors must be tested and proof of testing retained before they will be allowed on site. IET Code of Practice for In-service Inspection and Testing of Electrical Equipment, Table 7.1 provides guidance for formal inspections to be carried out and recorded at monthly intervals and combined inspection and testing every 3 months.
Conclusion
Construction sites are one of the more challenging environments to the safe use of electricity, as work is carried out in all weathers. Damp and wet conditions and sites which are constantly changing as work progresses can increase the risk of electric shock. Consequently, diligence and observation of relevant requirements are all the more necessary.
For more information on NAPIT, please visit: https://www.napit.org.uk/
