Excavations and Electrical Safety Flashcards

Before commencing excavation work on a construction site in Ireland, what must be done regarding underground services?

Answer: The location of all underground services (gas, electricity, water, telecoms) must be identified and marked before digging begins

Before any excavation, all underground services must be identified using service drawings, CAT scanning (Cable Avoidance Tool), and liaison with utility companies. Striking a live cable or gas main can be fatal.

What is the recommended minimum safe distance from an underground electrical cable when using a mechanical excavator?

Answer: 0.5 metres — hand digging should be used within 0.5 m of a known cable

Mechanical excavation should stop at least 0.5 metres from a known buried electrical cable. Hand digging should then be used to expose the cable safely. Even with marking, cables may not be exactly where records show.

What must be provided at the edge of every excavation over 2 metres deep on a construction site?

Answer: Barriers or guardrails to prevent people and vehicles from falling in

Excavations over 2 metres deep must have rigid barriers or guardrails around the edges. Warning signs alone are insufficient as people or vehicles can still fall or drive into unprotected excavations.

What is the primary risk of excavation collapse on a construction site?

Answer: Workers being buried alive or crushed, which can be fatal within minutes

An excavation collapse can bury a worker in seconds under tonnes of soil. Rescue is extremely difficult and often fatal. Ground conditions must be assessed and appropriate support (trench sheets, shoring, battering) installed.

What is the safe voltage for portable electrical tools used in damp or confined conditions on Irish construction sites?

Answer: 110 volts (centre-tapped to earth, with a maximum of 55 V to earth)

110 V centre-tapped to earth (CTE) is the standard safe voltage for construction sites in Ireland and the UK. The maximum voltage to earth is 55 V, significantly reducing the risk of a fatal shock compared to 240 V mains supply.

What colour are 110-volt cables and equipment typically marked on Irish construction sites?

Answer: Yellow

110 V construction equipment is typically identified by a yellow colour coding on cables, plugs, and transformers. This helps distinguish it from 230 V (blue) and 415 V (red) equipment.