NEBOSH CC Electrical Hazards on Site 2 — Questions and Answers
Question 1: What is the purpose of PAT testing (Portable Appliance Testing) on a construction site?
- To check that portable electrical equipment is safe and in good working order (Correct answer)
- To calibrate electrical test equipment
- To test the earthing resistance of the site installation
- To check the site power supply voltage
Correct answer: To check that portable electrical equipment is safe and in good working order
PAT testing involves inspection and electrical testing of portable electrical appliances to ensure they are safe. On construction sites, harsh conditions mean equipment deteriorates quickly and regular testing is essential.
Question 2: What is the safe distance that should be maintained from overhead power lines when using plant such as cranes or excavators?
- At least 3 metres from uninsulated overhead lines under 33kV (Correct answer)
- 1 metre from all overhead lines
- 5 metres from all overhead lines
- No fixed distance — just avoid contact
Correct answer: At least 3 metres from uninsulated overhead lines under 33kV
The safe working distance from uninsulated overhead lines depends on voltage, but for lines up to 33kV, a minimum exclusion zone of 3 metres is typically required. Higher voltage lines require greater distances and specialist assessment.
Question 3: What measures should be used when construction plant must work near overhead power lines?
- Goal posts, banksmen and exclusion zones (Correct answer)
- Only a banksman
- Insulating gloves for the operator
- Reducing machine speed only
Correct answer: Goal posts, banksmen and exclusion zones
When plant must work near overhead power lines, goal posts (height restriction barriers) must be erected to prevent plant from reaching the lines. A banksman should guide operations, and exclusion zones must be established. The power company should be contacted to consider de-energising the line.
Question 4: What is the meaning of 'isolation' in electrical safety?
- Disconnecting electrical equipment from all sources of supply and securing so it cannot be inadvertently re-energised (Correct answer)
- Turning off the main switch only
- Removing the fuse only
- Switching equipment to standby mode
Correct answer: Disconnecting electrical equipment from all sources of supply and securing so it cannot be inadvertently re-energised
Isolation means completely disconnecting equipment from all electrical energy sources and securing the isolation (e.g., with a lock) to prevent inadvertent re-energisation. Simply switching off is not sufficient — the supply must be physically disconnected.
Question 5: What is the risk of using a damaged extension lead on a construction site?
- Electrocution, electric shock or fire due to exposed conductors or poor connections (Correct answer)
- Only a risk of equipment damage
- The lead will automatically cut off the supply
- The lead will trip the MCB immediately
Correct answer: Electrocution, electric shock or fire due to exposed conductors or poor connections
A damaged extension lead with exposed conductors, damaged insulation or faulty connections can cause electric shock to anyone who touches it, and may cause arcing which leads to fire. All electrical leads must be regularly inspected.
Question 6: What colour coding is used for 415V three-phase electrical supply equipment on UK construction sites?
- Red (Correct answer)
- Blue
- Yellow
- Green
Correct answer: Red
415V three-phase electrical supply equipment on UK construction sites is colour-coded red. This distinguishes it from 230V (blue) and 110V (yellow) equipment, helping workers identify and use the correct supply.
NEBOSH CC Electrical Hazards on Site 2
What is the purpose of PAT testing (Portable Appliance Testing) on a construction site?