Electrical & Excavation Safety
Electrical hazards and underground services pose life-threatening risks on construction sites. This section covers electrical safety isolation procedures, working near overhead power lines (approach distances), locating underground services before excavation (Dial Before You Dig), excavation safety including shoring and benching, and confined space entry requirements.
Study Guide: Electrical & Excavation Safety
Review these sample questions before starting the practice test.
Q1: What is the safe approach distance for overhead powerlines when using a crane?
- A. 1 metre
- B. As close as needed
- C. The exclusion zone varies by voltage β at least 3 metres for lines up to 132 kV, and more for higher voltages β
- D. 10 centimetres
Safe approach distances for overhead powerlines vary by voltage: typically 3m for lines up to 132 kV, 6m for 132-330 kV, and 8m for above 330 kV. Always confirm with the electricity provider.
Q2: What is a residual current device (RCD)?
- A. A safety device that detects current imbalance and quickly cuts power to prevent electrocution β
- B. A type of electrical meter
- C. A battery backup system
- D. A circuit breaker for overloads only
An RCD detects imbalances between active and neutral conductors (indicating current leaking to earth, possibly through a person) and cuts power within milliseconds to prevent electrocution.
Q3: How often must RCDs be tested on a construction site?
- A. Once a year
- B. Only when they trip
- C. Daily (push-button test) and regularly by a competent person β
- D. Never β they are maintenance-free
RCDs on construction sites should be push-button tested daily before first use and regularly tested and tagged by a competent person (typically every 3 months) as per AS/NZS 3760.
Q4: What does "lockout/tagout" (LOTO) mean?
- A. Locking the site office and tagging the door
- B. Locking tools in a toolbox
- C. A procedure to isolate energy sources and prevent accidental re-energisation during maintenance or repair β
- D. Signing out equipment
Lockout/tagout is a safety procedure where energy sources (electrical, hydraulic, pneumatic) are physically isolated and locked, with tags attached to prevent accidental re-energisation during work.
Q5: Before digging or excavating, what must be done to locate underground services?
- A. Contact Dial Before You Dig (DBYD) to obtain plans showing underground utilities, then use a service locator β
- B. Nothing β just dig carefully
- C. Ask neighbours where pipes are
- D. Only check for water pipes
Before any excavation, contact Dial Before You Dig (DBYD) to obtain plans of underground services (gas, water, electricity, communications), then use a cable and pipe locator on site.
Q6: What is the purpose of shoring in an excavation?
- A. To support the walls of the excavation and prevent collapse onto workers β
- B. To make the excavation deeper
- C. To waterproof the excavation
- D. To store materials
Shoring supports the walls of an excavation using hydraulic, timber, or steel props to prevent soil collapse, which can trap, crush, or suffocate workers in the trench.
Q7: At what depth does an excavation generally require shoring or battering?
- A. Excavations deeper than 1.5 metres in general conditions β
- B. Any depth
- C. 5 metres
- D. 10 metres
As a general guide, excavations deeper than 1.5 metres may require shoring, benching, or battering to prevent collapse. However, risk assessment is needed for all depths based on soil conditions.
Q8: What is "battering" in the context of excavation safety?
- A. Sloping the sides of an excavation to a safe angle to prevent collapse β
- B. Hitting the ground with equipment
- C. A type of concrete technique
- D. Waterproofing the excavation walls
Battering (or benching) involves sloping the sides of an excavation back to a safe angle, reducing the risk of wall collapse. The angle depends on soil type and conditions.
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