Air circulation supply, no overload protection, no earth?!

[timhoward]

An agreed limitation of this EICR is that the air circulation unit circuit will not be inspected beyond the switchgear / controls due to no safe means of accessing units on roof of 4 story building. We're discussing how to resolve this. In meantime:

I'm inspecting the air circulation supply at the intake in the basement and two things immediately rang alarm bells.
The first thing that hit me is that while the outgoing SWA is properly earthed to the box, the box itself is on a wooden backplate, and there is wood between it and trunking, and there is no supply earth at all. A measurement of 0.55 ohms between MET (2m away) and the box confirms this. (same measurement to trunking). I've had the trunking cover off and confirmed there is no connection of any kind at all. I haven't yet established where the 0.55ohms is coming from and might not do as other end of SWA is on the inaccessible roof.





That said it's easy to add an earth strap to the MET and remove that question.

2nd thing that hit me was that incoming 6mm supply is connected directly to the bus-bar chamber (160A fused 3 phase upstream main switch).


But as I'm well within 3m of the bus-bar chamber and it's run in metal trunking I'm thinking that though it feels and looks a bit strange 433.2.2 (ii) would in fact apply to this situation?

 

[snowhead]

The Busbar layout is quite normal.
Every Chamber I worked on in over 50 years had multiple cables or copper bars of varying sizes.

The 0.55 maybe coming back through the steelwork the unit is bolted to on the roof or lightning conductor if the unit has one.

 

[timhoward]

The Busbar layout is quite normal.
Every Chamber I worked on in over 50 years had multiple cables or copper bars of varying sizes.

The 0.55 maybe coming back through the steelwork the unit is bolted to on the roof or lightning conductor if the unit has one.

Thank you for responding. I guess I was mainly thinking that 160A main switch fuses wouldn't normally be sufficient OCPD for the 6mm supply to fused isolator.
So I was looking for a reason that it's 'ok' and double checking 433.2.2 (ii) was the answer, basically it's less than 3m and installed to provide minimal risks?