What is the purpose of earthing an exposed metal luminaire, and when might it be omitted?

• A. To prevent electric shock by keeping the body at earth potential; it might be omitted for Class II double-insulated fittings.
• B. To improve lighting efficiency.
• C. To provide a return path for current in fault; always required.
• D. To reduce electromagnetic interference.

Answer: (A)

Earthing a metal luminaire is about safety: it gives any fault current a low-impedance path to earth so the metal housing stays at earth potential. If a live conductor invades the housing due to insulation failure, the fault current flows through the earth conductor and, because it is a strong, fast path, a protective device (fuse or circuit breaker) trips quickly. This reduces the risk of electric shock to someone who touches the fixture.

The reason earthing can be omitted is that some luminaires are Class II, meaning they are double-insulated and have no exposed conductive path to live. Their design ensures there isn’t a accessible metal part that could become live, so an earth connection isn’t required for safety.

The other ideas miss the core purpose: earthing isn’t about improving lighting efficiency, it isn’t always required for all equipment (especially Class II devices), and while a return path for fault current is related, calling it "always required" ignores the class of the fitting and its safety design.