CSCS Electrical Safety 4

Question 1

What does the abbreviation 'CTE' stand for in relation to 110V site transformers?

Accepted Answer

Centre-Tapped Earth

Answer

CTE stands for Centre-Tapped Earth. A 110V CTE transformer takes a 230V supply and steps it down to 110V, with the secondary winding centre-tapped to earth. This means the maximum voltage to earth is only 55V, which is considered a non-lethal level and provides enhanced safety on construction sites as required by BS 7671.

Question 2

What user checks should be carried out on a portable electrical tool before each use on a construction site?

Accepted Answer

Visual inspection of the plug, cable, and casing for damage, and checking the PAT test date is current

Answer

Before each use, operatives must visually inspect the plug (no cracks, pins straight), cable (no cuts, kinks, or exposed conductors), casing (no damage), and confirm the PAT test label is current. This is required under the Electricity at Work Regulations 1989 and PUWER 1998. A current PAT sticker does not guarantee the tool has not been damaged since the last test.

Question 3

What action should be taken if a 110V tool gives the user a tingling sensation during use?

Accepted Answer

Stop using it immediately, disconnect it, label it as defective, and report it to the supervisor

Answer

Any tingling sensation indicates an earth fault or insulation breakdown. The tool must be stopped immediately, disconnected, labelled as defective, and reported. Although 110V CTE limits voltage to earth to 55V, this can still cause injury particularly in wet conditions. Under the Electricity at Work Regulations 1989, defective equipment must be withdrawn from service.

Question 4

What is the purpose of earthing and bonding in a temporary electrical installation on a construction site?

Accepted Answer

To provide a low-resistance path to earth so that protective devices operate quickly in the event of a fault

Answer

Earthing and bonding provide a low-resistance path for fault current to flow to earth, enabling protective devices (fuses, MCBs, RCDs) to operate quickly and disconnect the supply. BS 7671 requires all exposed and extraneous conductive parts to be earthed and bonded to prevent them becoming live during a fault, which could cause electric shock.

Question 5

Under the Electricity at Work Regulations 1989, what standard must a voltage tester meet for safe isolation procedures?

Accepted Answer

It must comply with HSE Guidance Note GS38

Answer

HSE Guidance Note GS38 specifies the requirements for test instruments used during safe isolation. Voltage testers must have fused test leads, finger guards, insulated probes with limited exposed tips, and be proved on a known live source before and after testing. Non-contact voltage indicators (volt sticks) are useful aids but must not be relied upon as the sole means of proving dead.

CSCS Green Card Practice Test

CSCS Green Card Practice Test

CSCS Electrical Safety 4