Using Structural Frame as PE

[FirstTimePoster]

Hi there,

First time poster, thanks for your advice!

At the factory where I have just joined, we have some electricians that are mainly experienced in residential installs and not a lot of industrial.
I am an electrical engineer with electrical design experience (generally fixed installations/power electronics), but as always work in tandem with sparkies to get the best, compliant solution with respect to AS3000.

I arrived with an enclosure half built and electrical design completed by non-electrical people based on previous sub-contracted designs.
The transportable enclosure (AS3001 comes in to play) built has an external earth stud (welded to frame).
There are multiple inlets, and an onboard generator as backup (RCD protected etc).
Supply (and earthing) will normally be via inlets.
Equipment, a distribution board earth, and eventually a UPS system earth bar (out or our scope) have been bonded to the frame for the purposes of protective earth via earth cable/ring lug/threaded bolts, and not directly to a main earth bar.
All continuity tests pass as part of verification. Electrician does not seem worried.

Does this comply with section 5.3.2 of AS3000?
What is the consensus on this method?

 

[ElectroChem]

Oof, that's a bit of a gnarly one.

Exerpt from AS3000 5.3.2

5.3.2.1.3 Other materials
Materials other than copper or aluminium may be used as an earthing
conductor. In such cases, the conductor resistance shall be not greater
than that for a copper earthing conductor determined in accordance with
Clause 5.3.3, and the degree of corrosion resistance shall not be inferior to
other materials suitable for the purpose.

5.3.2.2 Conductor type
In addition, and subject to the special conditions of Clause 5.3.2.3, the
following media may be regarded as a protective earthing conductor:
(iii) Conductive framework used for mounting electrical equipment.

5.3.2.3 Special conditions
The following conditions apply where the components in Clause 5.3.2.2(i),
(ii), (iii) or (iv) are used for protective earthing:

(c) Conductive framework:
(i) General Conductive framework may be regarded as a protective
earthing conductor, provided that—
(A) the exposed conductive parts of electrical equipment are
mounted on, and in effective electrical contact with, the
framework; and
(B) the conductive framework is earthed by the connection of a
protective earthing conductor directly to the framework.

So, argument could be made both ways.
On the one hand, the heavy steel frame has a pretty decent resistance, especially as you've said it passed verification. So the installer could just say they're used an alternate earthing conductor.
On the other, by God that's dodgy. Run an earth you cheap b*st*rds.

Whilst it may technically comply, I would never put my name to something where at least the main earthing points weren't linked by proper earth cables. Meaning the inlets, DB earth bar and Genset earth bar should be properly linked, possibly all to the aforementioned central earth stud welded to the frame.

I've not got a copy of AS3001, it may have alternate requirements for protective earthing reticulation around a portable structure.