NEBOSH CC Electrical Hazards on Site 4 — Questions and Answers
Question 1: What minimum qualification should an electrician have to carry out electrical installation work on a construction site?
- Demonstrable competence such as an NVQ Level 3 or equivalent with relevant experience (Correct answer)
- Any City & Guilds qualification
- A first aid certificate
- Completion of a one-day electrical safety course
Correct answer: Demonstrable competence such as an NVQ Level 3 or equivalent with relevant experience
Electricians carrying out installation work should be competent, typically demonstrated by holding an NVQ Level 3 in Electrical Installations or equivalent, with relevant practical experience. Competence must be appropriate to the specific work.
Question 2: What is the function of a transformer on a construction site?
- To reduce the mains supply voltage (typically 230V) to the safer 110V used for portable tools (Correct answer)
- To increase the voltage for heavy plant operation
- To distribute power to multiple outlets simultaneously
- To monitor electrical energy consumption
Correct answer: To reduce the mains supply voltage (typically 230V) to the safer 110V used for portable tools
A step-down transformer reduces the mains 230V supply to the safer 110V used for portable tools on construction sites. The centre-tapped earth configuration ensures the maximum voltage to earth is only 55V, limiting shock severity.
Question 3: What is a 'dead leg' in the context of site electrical supply?
- A section of electrical cable that is energised but not connected to any load (Correct answer)
- An isolated section of decommissioned cable
- An electrical circuit that has failed
- A cable route with no bend radius restrictions
Correct answer: A section of electrical cable that is energised but not connected to any load
A dead leg is a section of energised electrical cable or pipe that is not connected to a load but remains live. These are hazardous because workers may not know the cable is live, especially if it appears abandoned or decommissioned.
Question 4: What is the safe method for testing whether electrical equipment is dead before commencing work?
- Use an approved voltage indicator or multi-meter to test between all conductors and earth (Correct answer)
- Touch the terminal briefly with the back of your hand
- Listen for buzzing sounds from the equipment
- Assume it is dead if the main switch is off
Correct answer: Use an approved voltage indicator or multi-meter to test between all conductors and earth
The only safe method is to use an approved voltage indicator (test instrument) to test between all live conductors and between each conductor and earth. The instrument itself should be tested before and after use to confirm it is working correctly.
Question 5: Which type of cable is suitable for use outdoors on a construction site?
- Heavy-duty rubber or armoured cable rated for outdoor use (Correct answer)
- Standard household PVC cable
- Extension leads designed for indoor office use
- Any cable with PVC insulation
Correct answer: Heavy-duty rubber or armoured cable rated for outdoor use
Outdoor construction site cables must be heavy-duty rubber-insulated or armoured cables designed to withstand the mechanical damage, moisture and UV exposure typical of site conditions. Standard indoor cables are not suitable.
Question 6: What does 'bonding' mean in electrical safety?
- Connecting metalwork together to equalise potential and reduce electric shock risk (Correct answer)
- Insulating metalwork to prevent current flow
- Earthing all metalwork to the main earth terminal
- Securing cables to the structure using cable ties
Correct answer: Connecting metalwork together to equalise potential and reduce electric shock risk
Bonding means connecting all exposed metalwork (pipework, structural steelwork, etc.) together so they are at the same electrical potential. This reduces the risk of electric shock if a fault causes one metalwork item to become live.
NEBOSH CC Electrical Hazards on Site 4
What minimum qualification should an electrician have to carry out electrical installation work on a construction site?