ET101 earth bonding - mechanical protection

You specifically ask about ET101 but I will only base my answer on its replacement. IS 10101 2020. A metal frame wall is not specifically mentioned in the examples below the definition of extraneous conductive part but given that such a wall is inside a building and highly unlikely to be introducing “local” earth potential, my opinion is that it is not a part that would be considered exposed or extraneous. Main protective bonding is required for structural steel and you sometimes see hangers from the SS to the metal frame so I guess that such fortuitous contact now has the frame introducing MET potential rather than “local” earth potential. I have “local” in parentheses because it was not mentioned in ET 101 and there is no definition of that term in IS10101.

With respect to the gauge of the metal sheath or plate protecting cables in walls, no dimensions are provided. However, the metal is required by clause 522.6.5. to be earthed thus one would imagine that it should be robust enough to Handle the fault current long enough to operate the circuit PD. Regulation 522.6.204 in 7671 might provide reasonable guidance on what might be acceptable.

Just to clarify, there is no requirement for metal covering where the distance to the wiring measured from the REVERSE side of the wall is more than 50mm and the cables are run in a straight vertical or horizontal fashion to the point.

Unlike 522.6.203 in 7671, there is no requirement in IS10101 to haveRCD protection in metal frame partitions where cables are not protected by an earthed metal covering, irrespective of depth.