Typical Examination Questions based on Element 6

1.	a) Describe the possible effects of electricity on the body. b) Outline FOUR factors that may affect the severity of injury from contact with electricity.	(4) (4)
	Affects such as interference with nerve/muscle action, tissue burns and cardio-respiratory effects, in particular the risk of fatal injury due to disruption of heart rhythm. As far as tissue burns are concerned, candidates should have identified as the main sites of damage the entry and exit points and warned of the possibility of damage to internal organs. Better responses included reference to secondary injuries such as head injuries caused by falls following electric shock. Factors such as the voltages involved the length of contact time, the route taken through the body, and the general health and age of the person involved. Additional factors that might affect the severity of the injury include the dryness of the skin, natural body resistance, ground conditions and the type of footwear being worn at the time.
2.	Outline the measures to be taken to minimize the risk of shock from the use of electric hand tools.	(8)
	Measures include: The use of reduced low voltage trough a transformer centre-tapped to earth The use of residual current devices or earth leakage protection. The protection and safe positioning of supply cables Using double-insulated equipment Using cordless (battery operated) equipment Ensuring the correct rating of fuses Introducing a system for routine visual inspection and testing of cables and equipment
3.	HSG65 Electricity at Work-Safe Working Practices gives guidance on the frequency of inspection for such equipment. State frequencies for the inspection and testing of electrical hand held tools and associate equipment used on a construction site and support your answers with appropriate examples.	(8)
	A hand held tool and equipment should be visually inspected before use, including cables, cord grips, casings and plugs. 230 volt equipment should be tested before first use and then at monthly intervals while a formal weekly inspection is also required. 110 volt equipment should be tested before first use and then at three monthly intervals while a formal monthly inspection is also required. Extension leads should have an initial test before first use followed and then at monthly intervals while a formal weekly inspection is also required
4.	List the items that should be included on an inspection checklist designed to ensure the safety of portable electrical hand-tools.	(8)
	Items on list could include: Equipment appropriate for the task and environment, equipment tested, plugs, connectors and cables free from damage or defect, correct wiring and sound connections, fuses and other means of preventing excess current in place and of correct rating, accessibility and appropriate means of isolation and system not overloaded.
5.	In relation to the use of electrical cables and plugs in the workplace: (i) Identify FOUR examples of faults and bad practice that could contribute to electrical accidents. (ii) Outline the corresponding precautions that should be taken for each of the examples identified in (i).	(4) (4)
	Examples include: Failure to select right equipment for the environment (armoured or heat resistant cables may be require). Incorrect rating of fuses. Ineffective or discontinuous earthing. Overload of Socket outlets. Cables unnecessarily long (or too short). The use of coiled extension leads. Poorly wired plugs (wires under tension or outer protective sheath not clamped). The use of defective cables and plugs. (ii) Precautions should have followed automatically from the deficiencies listed in (i)

Element 6 Electrical Hazards and Control

The section of the NCC1 describes what hazards are posed by the presence of electricity on a construction site, the hazards posed by the use of electricity and associated equipment such as hand tools, extension cables, portable and fixed lighting, temporary supplies from mains or generators.

The use of electrical hand tools is considered a major hazard on construction sites, therefore there are guidelines on the inspection and record keeping for these tools or equipment.

Testing

• Every installation should be tested in accordance with BS 7671: Requirements for Electrical Installation, before use on site, at three-monthly intervals or shorter periods if necessary.
  
• The record of any testing and inspections should be made by a responsible person on the appropriate certificates.
  
• Testing and inspections must include:
  
  • a visual inspection
    
  • the continuity of final circuit conductors
    
  • the continuity of protective conductors
    
  • the earth electrode resistance
    
  • the insulation resistance
    
  • polarity
    
  • the earth fault loop impedance
    
  • the correct operation of residual current devices and fault voltage operated protective devices.
    

Suggested inspection and test frequencies for electrical equipment on construction sites

Equipment/application	Voltage	User check	Formal visual	Combined inspection and check
Battery operated power tools and torches	Less than 25 volt	No	No	No
25V Portable hand lamps	25 volt secondary winding from transformer	No	No	No
50V portable hand lamps	Secondary winding centre tapped to earth (25 volt)	No	No	Yearly
110V portable and hand held tools, extension leads, site lighting, movable wiring systems and switchgear	Secondary winding centre tapped to earth (50 volt)	Weekly	Monthly	Before first use and then 3 monthly
230V portable and hand held tools, extension leads and portable floodlighting	230 volt mains supply through 30mA RCD	Daily/every shift	Weekly	Before first use and then monthly
230V equipment such as lifts, hoists and fixed floodlighting	230 volt supply fuses or MCBs	Weekly	Monthly	Before first use and then 3 monthly
RCDs fixed **		Daily/every shift	Weekly	* Before first use and then 3 monthly
Equipment in site offices	230 volt office equipment	Monthly	6 monthly	Before first use and then yearly
* Note: RCDs need a different range of tests to other portable equipment, and equipment designed to carry out appropriate tests on RCDs need to be used. ** It is recommended that portable RCDs are tested monthly

Key points

• Electricity can be a killer - you cannot see it and may not know that an item of equipment is live – until you touch it.
  
• Buried cables and those inside partition walls or other 'hidden places' are just waiting for the unwary to accidentally damage the cable and cause themselves serious injury or even death.
  
• The electrical distribution systems found on site tend to operate in a harsh environment and must be treated with care and respect.
  
• No-one other than a qualified electrician must alter the site distribution system.
  
• Ideally, apart from mains-powered equipment in site offices, all other equipment such as electrical hand tools will run off a 110 volt supply.
  
• The safest electrically powered tools and equipment are those that run off batteries.
  

Causes of electric shock

• Contact between a live conductor and earth.
  
• Contact between phase and neutral conductors (as the body is likely to have less electrical resistance than any load).
  
• According to the Health and Safety Executive, the majority of electrical accidents happen because people are working on or close to equipment which is either, assumed to be dead but is, in fact, live
  
• known to be live, but workers have not received adequate training, lack adequate equipment or have not taken adequate precautions
  

Legislation covering the use of electricity on construction sites

• The Management of Health and Safety at Work Regulations 1999 (as amended)
  
• The Construction (Design and Management) Regulations 2007
  
• The Electricity at Work Regulations 1989
  
• The Provision and Use of Work Equipment Regulations 1998 (as amended)
  

Working near overhead power lines

The local electricity company must be consulted before any work starts and a safe system of work must be devised and implemented. Other suppliers may also need to be consulted, for example, Local Authorities, National Grid and other electricity companies.

Special attention should be paid to traffic movements and the erection of appropriate warning sign and barrier (goalposts) should be erected, this apply to the use of excavating machinery near overhead power lines.