CSCS Electrical Safety 2 — Questions and Answers
Question 1: What colour is the reduced low-voltage 110V plug and socket used on UK construction sites?
- Blue
- Yellow (Correct answer)
- Red
- Black
Correct answer: Yellow
110V plugs and sockets are coloured yellow in the UK, in accordance with BS EN 60309. Blue denotes 230V single phase, red denotes 415V three-phase. This colour coding helps operatives quickly identify the voltage and select the correct equipment.
Question 2: What does a CAT scanner detect when used before excavation work near electrical cables?
- Only metallic water pipes
- Underground power cables, metal pipes, and other buried services (Correct answer)
- Soil contamination levels
- Concrete reinforcement bars only
Correct answer: Underground power cables, metal pipes, and other buried services
A Cable Avoidance Tool (CAT) detects underground power cables, telecommunications cables, and metallic pipes using different detection modes (power, radio, and Genny modes). HSE guidance PG381 requires CAT and Genny surveys before any excavation to locate buried services and prevent cable strikes.
Question 3: Under BS 7671, what is the maximum disconnection time for a 230V final circuit protected by an RCD in a TT earthing system?
- 5 seconds
- 0.2 seconds (Correct answer)
- 0.4 seconds
- 1 second
Correct answer: 0.2 seconds
BS 7671 (IET Wiring Regulations) specifies a maximum disconnection time of 0.2 seconds for socket-outlet circuits in TT systems protected by a 30mA RCD. This rapid disconnection time ensures that any earth fault is cleared before a lethal shock can occur.
Question 4: What must be done if an underground electrical cable is accidentally damaged during excavation work?
- Cover it with soil and continue working
- Attempt to repair it with insulation tape
- Evacuate the area immediately, report to the site manager, and contact the utility provider (Correct answer)
- Ignore it if no sparking is visible
Correct answer: Evacuate the area immediately, report to the site manager, and contact the utility provider
If an underground cable is struck, all personnel must evacuate the immediate area as the cable may still be live. The site manager must be informed, the area secured, and the relevant Distribution Network Operator (DNO) contacted immediately. Under the Electricity at Work Regulations 1989, continuing to work near a damaged cable is extremely dangerous and unlawful.
Question 5: What is the minimum IP (Ingress Protection) rating generally recommended for electrical equipment used outdoors on UK construction sites?
- IP20
- IP44 (Correct answer)
- IP67
- IP00
Correct answer: IP44
IP44 is the minimum rating generally recommended for electrical equipment used outdoors on construction sites, providing protection against solid objects over 1mm and water splashing from all directions. BS 7671 and HSE guidance specify that equipment must be suitable for the environment in which it is used.
Question 6: What type of cable management practice should be followed to prevent tripping hazards on a construction site?
- Cables can be left loose across walkways if they are brightly coloured
- Cables should be routed overhead or protected by cable covers and kept away from walkways where practicable (Correct answer)
- Cables should be buried in shallow trenches across footpaths
- Cable management is only required in office areas, not on construction sites
Correct answer: Cables should be routed overhead or protected by cable covers and kept away from walkways where practicable
Under the Workplace (Health, Safety and Welfare) Regulations 1992 and CDM Regulations 2015, cables must be managed to prevent tripping hazards. Best practice is to route cables overhead on dedicated supports or use proprietary cable covers where they cross walkways. Trailing cables are a leading cause of slips, trips, and falls on construction sites.
CSCS Electrical Safety 2
What colour is the reduced low-voltage 110V plug and socket used on UK construction sites?