An appliance technician is investigating the wiring of an electrical device designed for connection to a standard UK mains supply. They measure the potential differences across three incoming lines, $P$, $Q$, and $R$, which correspond to the live, neutral, and earth connections (not necessarily in that order).

The setup and measurements are shown in the diagram below:

Under normal operating conditions, the wire connected to line $R$ carries no current and is designed solely as a path to ground for safety.

Which option correctly identifies lines $P$, $Q$, and $R$?