CSCS Electrical Safety 2 — Questions and Answers
Question 1: Why is 110V preferred over 230V for portable tools on construction sites?
- It uses less electricity and reduces running costs
- The centre-tapped earth system limits maximum shock voltage to 55V, greatly reducing the risk of a fatal shock (Correct answer)
- It requires smaller, lighter cables
- 230V tools are not available for construction use
Correct answer: The centre-tapped earth system limits maximum shock voltage to 55V, greatly reducing the risk of a fatal shock
In a 110V CTE system the midpoint of the transformer secondary is earthed, so the maximum voltage to earth at either conductor is only 55V, significantly reducing electrocution risk.
Question 2: What does a Residual Current Device (RCD) do?
- Reduces the supply voltage to a safe level
- Detects an imbalance caused by an earth fault and rapidly disconnects the power supply (Correct answer)
- Tests electrical equipment to confirm it has passed PAT
- Increases the working life of power tools
Correct answer: Detects an imbalance caused by an earth fault and rapidly disconnects the power supply
An RCD continuously monitors the current balance between live and neutral conductors; any leakage to earth triggers a near-instant disconnection, protecting against electric shock.
Question 3: Which of the following is a visual warning sign that electrical equipment may be unsafe to use?
- The cable is neatly coiled and secured
- The plug is firmly fitted with no missing pins
- The outer casing is cracked or has pieces broken away (Correct answer)
- The equipment carries a current PAT test label
Correct answer: The outer casing is cracked or has pieces broken away
A cracked or broken casing can expose live internal components, creating a direct electrocution hazard for the user.
Question 4: Who is qualified to carry out repairs on electrical equipment or installations on a construction site?
- Any worker who feels confident doing so
- The site manager after completing the site induction
- A competent electrician with the relevant training and qualifications (Correct answer)
- Only the original equipment manufacturer
Correct answer: A competent electrician with the relevant training and qualifications
Only a competent electrician with appropriate training, knowledge, and experience should perform electrical repairs to ensure the work is carried out safely and correctly.
Question 5: What is the primary function of the earth wire in an electrical circuit?
- To carry the main working current to the equipment
- To provide a low-resistance fault path so protective devices operate and disconnect the supply (Correct answer)
- To reduce the operating voltage of the tool
- To improve the efficiency and performance of the motor
Correct answer: To provide a low-resistance fault path so protective devices operate and disconnect the supply
The earth wire (green and yellow) provides a safe fault-current path that causes fuses or circuit breakers to operate, removing the dangerous voltage before a person can be shocked.
Question 6: What steps should be taken before excavating in an area where underground electrical cables may be present?
- Start digging slowly and look for cables as you go
- Obtain service drawings, use a Cable Avoidance Tool (CAT), and follow safe digging procedures (Correct answer)
- Ask a colleague whether they remember seeing any cables
- Work as quickly as possible to minimize exposure time
Correct answer: Obtain service drawings, use a Cable Avoidance Tool (CAT), and follow safe digging procedures
Service drawings locate known cables on paper, a CAT scanner detects live cables by their electromagnetic field, and safe digging procedures ensure workers avoid striking buried services.
Question 7: Which specialist tool is used to detect the electromagnetic field emitted by buried electrical cables before excavation?
- A standard metal detector
- A Cable Avoidance Tool (CAT) (Correct answer)
- A thermal imaging camera
- A standard electric drill set to reverse
Correct answer: A Cable Avoidance Tool (CAT)
A Cable Avoidance Tool (CAT) is purpose-built to detect the electromagnetic field radiated by live cables, allowing workers to locate and avoid them during excavation.
CSCS Electrical Safety 2
Why is 110V preferred over 230V for portable tools on construction sites?