Earthing in PVC-U Conduit Systems
This one is worth stating plainly, because it is the single most common misunderstanding when a contractor moves from steel conduit to PVC-U: the containment provides no earth path.
Also searched as: earth terminal, earthing terminal, MET1, CPC, circuit protective conductor, earth screw
Why a separate earth is essential
Steel conduit systems can serve as the circuit protective conductor. PVC-U cannot — the properties that make it corrosion proof, lightweight and safe to handle also make it an insulator. Every circuit run in PVC-U conduit requires a separate circuit protective conductor sized and installed to BS 7671.
The MET1 terminal
Every Marshall-Tufflex box has provision for the MET1 brass earthing terminal, rated at 15 amp, giving a proper mechanical termination for the CPC at each box rather than a conductor twisted and taped. Code IMMET1, supplied 100 per pack.
Inspection and testing
Because the earth path is entirely in the conductors, continuity testing at every accessory and box matters more than on a metallic system. Plan draw-in points and access boxes so that the CPC can actually be inspected at the points where it is jointed.