CSCS Ireland Excavations and Electrical Safety 2 — Questions and Answers
Question 1: What is a Residual Current Device (RCD) and why is it used on construction sites?
- A safety device that detects earth faults and cuts power within milliseconds to prevent fatal electrocution (Correct answer)
- A device that regulates voltage to tools
- A piece of equipment that measures electrical consumption
- A lockout device for isolating equipment during maintenance
Correct answer: A safety device that detects earth faults and cuts power within milliseconds to prevent fatal electrocution
An RCD detects imbalances in current flow (indicating a fault or someone touching a live conductor) and disconnects power in 30 milliseconds or less, potentially before a fatal shock can be delivered.
Question 2: What should a worker do if they find a damaged electrical cable on a construction site?
- Stop using the equipment, isolate the power source, report it immediately, and tag the equipment out of service (Correct answer)
- Wrap the damaged section in insulating tape and continue working
- Continue using it carefully, avoiding the damaged section
- Leave it for the electrician to find at the next inspection
Correct answer: Stop using the equipment, isolate the power source, report it immediately, and tag the equipment out of service
A damaged cable is a serious electrical hazard. The equipment must be immediately taken out of service, the power isolated, the defect reported, and the item tagged to prevent accidental use until properly repaired.
Question 3: What is the correct approach to excavating close to overhead electricity lines on a construction site?
- Establish safe exclusion zones, use goal posts to limit vehicle height, and liaise with the network operator (Correct answer)
- Work quickly to minimise time spent near the lines
- Post a lookout person to watch for contact
- Only work during daylight hours
Correct answer: Establish safe exclusion zones, use goal posts to limit vehicle height, and liaise with the network operator
Work near overhead lines requires establishing safe clearance zones, erecting goal post-type barriers to limit plant height, and coordinating with the network operator who may need to isolate or divert the line.
Question 4: What is the purpose of trench sheeting or shoring in an excavation?
- To support the sides of the excavation and prevent soil collapse (Correct answer)
- To cover the excavation when not in use
- To channel groundwater away from the excavation
- To provide a working platform inside the trench
Correct answer: To support the sides of the excavation and prevent soil collapse
Trench sheets, shoring boxes, or drag boxes support the walls of an excavation, preventing soil from collapsing onto workers. They must be designed or selected based on soil type, depth, and surcharge loads.
Question 5: How often must an excavation on a construction site be formally inspected in Ireland?
- Before every work shift, after any ground movement or blasting, and after any unexpected fall of material (Correct answer)
- Once a week on Monday morning
- Only at the start of the excavation
- Only when it exceeds 3 metres in depth
Correct answer: Before every work shift, after any ground movement or blasting, and after any unexpected fall of material
Excavations must be inspected by a competent person before each shift, after any event that may have affected stability (rain, vibration, blasting), and when there is any indication of danger.
Question 6: What is the meaning of 'isolation' in electrical safety on a construction site?
- Disconnecting equipment from all sources of electrical energy and preventing accidental reconnection through lockout/tagout (Correct answer)
- Turning off a tool with its on/off switch
- Wrapping cables in insulation
- Moving electrical equipment away from water
Correct answer: Disconnecting equipment from all sources of electrical energy and preventing accidental reconnection through lockout/tagout
Electrical isolation means physically disconnecting all energy sources and securing the isolation point (typically with a lock and personal danger tag) so the equipment cannot be accidentally re-energised while work is being carried out.
CSCS Ireland Excavations and Electrical Safety 2
What is a Residual Current Device (RCD) and why is it used on construction sites?