NEBOSH CC Electrical Hazards on Site 1 — Questions and Answers
Question 1: What voltage is used as the standard supply for portable power tools on UK construction sites to reduce electrocution risk?
- 110V centre-tapped to earth (CTE) (Correct answer)
- 230V single phase
- 415V three phase
- 12V battery only
Correct answer: 110V centre-tapped to earth (CTE)
110V centre-tapped to earth (CTE) is used on UK construction sites. The transformer centre tap is earthed so the maximum voltage to earth is 55V, significantly reducing the severity of an electric shock compared to 230V.
Question 2: What colour is typically used for 110V electrical supply equipment on UK construction sites?
- Yellow (Correct answer)
- Blue
- Red
- Orange
Correct answer: Yellow
110V electrical equipment and leads on UK construction sites are colour-coded yellow to distinguish them from 230V (blue for single phase) and 415V (red for three phase) equipment, helping workers identify the correct supply voltage.
Question 3: What is the primary hazard when using electrical equipment near water on a construction site?
- Electrocution from current passing through the water (Correct answer)
- Damage to electrical cables
- Short circuit causing equipment failure
- Reduced power output
Correct answer: Electrocution from current passing through the water
Water is a conductor of electricity. When electrical current passes through water, anyone in contact with the water who is also touching an earthed surface can receive a lethal electric shock.
Question 4: What device provides protection against electrocution by detecting earth leakage current and cutting off the supply within milliseconds?
- Residual Current Device (RCD) (Correct answer)
- Miniature Circuit Breaker (MCB)
- Fuse
- Isolation switch
Correct answer: Residual Current Device (RCD)
A Residual Current Device (RCD) detects any difference between the current in the live and neutral conductors, indicating a fault or leakage to earth, and disconnects the supply within 30 milliseconds — fast enough to prevent electrocution.
Question 5: What does 'dead working' mean in the context of electrical safety?
- Working on electrical equipment that has been isolated and proved dead before work begins (Correct answer)
- Working on live electrical equipment
- Working after normal business hours
- Working in areas with no electrical supply
Correct answer: Working on electrical equipment that has been isolated and proved dead before work begins
Dead working means all electrical equipment and conductors in the work area are isolated from the electrical supply and proved dead (tested) before work begins. This is the safest method of working on electrical systems.
Question 6: Which regulations govern the safe use of electrical equipment in the workplace?
- Electricity at Work Regulations 1989 (Correct answer)
- Health and Safety at Work etc. Act 1974
- Electrical Equipment (Safety) Regulations 2016
- Provision and Use of Work Equipment Regulations 1998
Correct answer: Electricity at Work Regulations 1989
The Electricity at Work Regulations 1989 (EAW Regs) set out the legal requirements for the safe use, maintenance and operation of electrical equipment in the workplace, including construction sites.
NEBOSH CC Electrical Hazards on Site 1
What voltage is used as the standard supply for portable power tools on UK construction sites to reduce electrocution risk?