CSCS Electrical Safety 3 — Questions and Answers
Question 1: What is the purpose of a permit-to-work system for electrical work on construction sites?
- To record the hours worked by electricians
- To formally control high-risk electrical work by documenting the hazards, precautions, and authorisation (Correct answer)
- To track material costs for electrical installations
- To schedule routine maintenance visits
Correct answer: To formally control high-risk electrical work by documenting the hazards, precautions, and authorisation
A permit-to-work is a formal documented system used to control high-risk activities including live electrical work. It identifies hazards, specifies precautions, and requires authorisation before work begins. The Electricity at Work Regulations 1989 require that no live working is undertaken unless it is unreasonable to work dead, and a permit system manages this risk.
Question 2: Under what circumstances is live electrical working permitted on a construction site under Regulation 14 of the Electricity at Work Regulations 1989?
- Whenever it is more convenient than isolating the supply
- Only when it is unreasonable to work dead, and suitable precautions are in place (Correct answer)
- When the operative holds a CSCS card
- Live working is never permitted under any circumstances
Correct answer: Only when it is unreasonable to work dead, and suitable precautions are in place
Regulation 14 of the Electricity at Work Regulations 1989 states that live working is only permitted when it is unreasonable in all circumstances for the equipment to be dead, and suitable precautions (including technical knowledge, insulated tools, and accompaniment) are taken to prevent injury.
Question 3: What is the recommended trip current for an RCD providing additional personal protection on a construction site?
- 100mA
- 300mA
- 30mA (Correct answer)
- 500mA
Correct answer: 30mA
A 30mA RCD is recommended for additional personal protection as it will disconnect the supply before the current reaches a level that could cause a fatal electric shock. BS 7671 specifies 30mA RCDs for socket-outlet circuits and for circuits supplying mobile equipment outdoors. Higher rated RCDs (100mA, 300mA) provide fire protection but not reliable personal shock protection.
Question 4: What documentation should be checked before using a portable generator on a construction site?
- Only the fuel receipt
- The PAT test certificate, maintenance records, and confirmation it provides 110V CTE output (Correct answer)
- The manufacturer's marketing brochure
- No documentation is required for generators
Correct answer: The PAT test certificate, maintenance records, and confirmation it provides 110V CTE output
Before using a portable generator, operatives should verify it has a current PAT test, is properly maintained, and provides 110V via a centre-tapped earth (CTE) transformer for construction site use. The Provision and Use of Work Equipment Regulations 1998 (PUWER) require that all work equipment is suitable, properly maintained, and inspected.
Question 5: What is the safe distance that must be maintained from 33kV overhead power lines when operating a crane or MEWPs?
- 3 metres
- 6 metres (Correct answer)
- 15 metres
- 1 metre
Correct answer: 6 metres
HSE guidance note GS6 specifies a minimum safe distance of 6 metres from overhead power lines up to 33kV for mobile plant such as cranes and MEWPs. This accounts for the reach of equipment, cable sag, and wind movement. If work must take place within this zone, the DNO must be contacted to discuss isolation or diversion.
Question 6: Who is legally responsible for ensuring that a construction site's temporary electrical installation complies with BS 7671?
- The client only
- The architect who designed the building
- The principal contractor and any electrical contractor undertaking the installation (Correct answer)
- The local council building control officer
Correct answer: The principal contractor and any electrical contractor undertaking the installation
Under CDM Regulations 2015, the principal contractor has overall responsibility for site safety including temporary electrical installations. The electrical contractor carrying out the work must also ensure compliance with BS 7671. Both parties share responsibility for ensuring the installation is designed, installed, inspected, and tested to the required standard.
CSCS Electrical Safety 3
What is the purpose of a permit-to-work system for electrical work on construction sites?