Electrical Safety Flashcards

What class of electrical equipment relies solely on double insulation for protection rather than an earth connection?

Answer: Class II

Class II equipment (marked with the double square symbol) relies on double or reinforced insulation for protection against electric shock and does not require an earth connection. The Electricity at Work Regulations 1989 recognise double insulation as a valid protective measure. Class I equipment relies on an earth connection, while Class III uses Safety Extra-Low Voltage (SELV).

What is the maximum recommended length of an extension lead used with 110V equipment on a construction site?

Answer: 15 metres

Extension leads for 110V equipment should generally not exceed 15 metres to minimise voltage drop and reduce the risk of damage. Longer leads increase resistance, can cause overheating, and create additional tripping hazards. HSE guidance recommends keeping leads as short as practicable and fully unwound from any drum to prevent overheating.

What action is required under the Electricity at Work Regulations 1989 if an electrical distribution board on site is found to have a broken door or missing cover?

Answer: It must be immediately taken out of service, isolated, and repaired before being re-energised

Under Regulation 4 of the Electricity at Work Regulations 1989, all electrical systems must be constructed and maintained to prevent danger. A broken door or missing cover exposes live parts and creates a risk of electric shock, water ingress, and accidental contact. The board must be isolated immediately, repaired, and re-inspected before being returned to service.

What is the role of the DNO in relation to construction site electrical supplies?

Answer: The Distribution Network Operator provides and maintains the electricity supply up to the meter point and must be consulted about nearby overhead or underground cables

The Distribution Network Operator (DNO) owns and maintains the electricity distribution network. They provide the supply to the site's meter point and must be consulted when work is planned near their overhead lines or underground cables. Under the Electricity at Work Regulations 1989 and HSE guidance GS6, the DNO can arrange diversions, isolations, or additional protection.

What additional precaution must be taken when using electrical equipment in a confined space on a construction site?

Answer: Use battery-powered or SELV (Safety Extra-Low Voltage) equipment not exceeding 25V, and ensure RCD protection is in place

In confined spaces, the risk of electric shock is greatly increased due to the proximity of earthed metalwork and potentially damp conditions. BS 7671 and HSE guidance require the use of SELV equipment (not exceeding 25V) or battery-powered tools wherever practicable. If 110V equipment must be used, additional RCD protection at 30mA is essential.

How should temporary site lighting circuits be protected on a construction site according to BS 7671?

Answer: By 30mA RCD protection, with circuits rated at 110V where portable, and fixed lighting at 230V only where inaccessible to site operatives

BS 7671 requires temporary site lighting to be protected by 30mA RCDs. Portable and temporary lighting must operate at 110V CTE. Fixed lighting at 230V is only permissible where it is out of reach of site operatives and adequately protected. All lighting circuits must be properly installed, tested, and maintained throughout the project.