In earth fault loop impedance measurements, what do R1 and R2 represent?

• A. R1 and R2 are resistors used to limit current in the RCD coil.
• B. R1 and R2 are only used in lighting circuits.
• C. R1 and R2 refer to phase conductor resistances in loop.
• D. R1 and R2 are the earth fault loop impedance components used when assessing earth continuity; measured values indicate path resistance.

Answer: (D)

When checking earth fault loop impedance, you’re looking at the path fault current would take from the live conductor, through the protective device, along the conductors, and back via the earth to the source. This loop has two main resistive parts: R1 is the resistance of the phase conductor from the supply to the fault point, and R2 is the resistance of the protective/earth return path back to the source. Adding these together (and including any earth electrode resistance in some systems) gives the total earth fault loop impedance. This total tells you how easily fault current can flow and whether the protective device will trip quickly enough to clear the fault. So R1 and R2 are the components of the earth fault loop impedance that quantify the path resistance, which is exactly what the measurement assesses. The other statements don’t fit because components described as current-limiting parts in an RCD coil or as exclusive to lighting circuits don’t describe the fault-loop path used for continuity and disconnection timing.