Can an extraneous conductive part be used as a legitimate earth fault path?

In BS 7671 terms it is permitted to use extraneous-conductive-parts as protective conductors (see 543.2.1 (vii) ... with a few conditions (see 543.2.6) which pretty much boil down to it being electrically adequate (impedance, fault withstand, etc.) and reliable (not likely to be removed by other trades etc. or nullified by corrosion) On the face of it shipping container could well be fine.

Depending on the nature of the contents on the container, it might not be a BS 7671 matter though - if the whole thing counts as a machine or other assembly that falls under a specific equipment standard, other rules might apply.

   - Andy.

It also depends where the container itself is to be dropped. If it is outdoors on its skids it will haf heartedly serve as its own electrode, but if being supplied TT, as a lot of outdoor kit like portakabins is, it will need its own electrode. (2 wires cheaper than 3, and L-N reversal is less dangerous if you are not using N to derive a local CPC/earth.) I'd expect provision such as large studs and nuts with anti-shake washers for an electrode to be connected as well as to terminate any CPC of the incomer.

If the container is to be inside a dry structure like a hanger with a concrete floor, then  to use the building supply CPC alone is more sense, but it needs adequate cross section for the maximum fault current.

If for example things like 13A sockets get their CPC by a fly lead to the body of the container, rather than dedicated wire, while OK, then it needs to be mechanically sound (welded nuts or similar, not friction fit ) -when done well it is possible to use the container as MET and also CPC for all internal circuits, however, personally I'd be inspecting pretty closely if that was the case, and looking for lock-washers and giving everything a jolly good tug before accepting that approach.

Equally, if the kit in the container has externally connected services, like water cooling systems, or for the maximum complexity, the container includes the option of a diesel genset as well, then there are multiple requirements to satisfy, such as those for main bonds as well as the actual CPC cross-section, and the cpc and MET may need a far larger cross section, than the normal load alone suggests.

So, in summary, it can be OK if properly done, but more info is needed,  especially if it is one of the harder corner cases.

Things like this https://marshallgroup.com/en/land-maritime/deployable-infrastructure are only containers too, but wiring a lot of those together gets very complex very quickly.

Mike.

It also depends where the container itself is to be dropped. If it is outdoors on its skids it will haf heartedly serve as its own electrode, but if being supplied TT, as a lot of outdoor kit like portakabins is, it will need its own electrode. (2 wires cheaper than 3, and L-N reversal is less dangerous if you are not using N to derive a local CPC/earth.) I'd expect provision such as large studs and nuts with anti-shake washers for an electrode to be connected as well as to terminate any CPC of the incomer.

If the container is to be inside a dry structure like a hanger with a concrete floor, then  to use the building supply CPC alone is more sense, but it needs adequate cross section for the maximum fault current.

If for example things like 13A sockets get their CPC by a fly lead to the body of the container, rather than dedicated wire, while OK, then it needs to be mechanically sound (welded nuts or similar, not friction fit ) -when done well it is possible to use the container as MET and also CPC for all internal circuits, however, personally I'd be inspecting pretty closely if that was the case, and looking for lock-washers and giving everything a jolly good tug before accepting that approach.

Equally, if the kit in the container has externally connected services, like water cooling systems, or for the maximum complexity, the container includes the option of a diesel genset as well, then there are multiple requirements to satisfy, such as those for main bonds as well as the actual CPC cross-section, and the cpc and MET may need a far larger cross section, than the normal load alone suggests.

So, in summary, it can be OK if properly done, but more info is needed,  especially if it is one of the harder corner cases.

Things like this https://marshallgroup.com/en/land-maritime/deployable-infrastructure are only containers too, but wiring a lot of those together gets very complex very quickly.

Mike.