Industrial bonding

[Jc1996]

Hi all I’ve always struggled getting my head round bonding in an industrial setting I think a fair amount of it I’m overthinking but I’ve been told many different things. My question is regarding bonding unistrut. For example the unistrut is bolted directly to the ground with cable tray attached to it, there may be a junction box with an SWA terminated to and off that SWA there’s a fly lead to the unistrut or cable tray. Some times it’s done sometimes it’s not just wanted to clear my head up around this confusion

 

[Andy™]

is it extraneous or an exposed conductiv part?

 

[Jc1996]

Well that’s the thing the unistrut outside is technically in contact with the earth as it’s bolted so I’d say extraneous but In some cases it’s just connected to the closes swa banjo and 6mm fly lead. 

 

[Sidewinder]

Does this unistrut and parts in contact with it enter the equipotential zone within the premises or does it remain outside at all times?

 

[Jc1996]

Remains outside the whole installation? 

 

[Sidewinder]

So it's not in the equipotential zone?

 

[Jc1996]

No it’s not 

Basically I’m struggling to understand why the installation guys run fly leads to unistrut when all its doing is supporting say an isolator. 

 

[Andy™]

because he's incompetant and hasnt moved on from a previous edition where 'bond everything, including window frames' was a thing...

 

[Sidewinder]

The only reason that it would be necessary to bond Unistrut outside would be under EN 60204-1:2018. Under 7671 you could be caused an issue by exporting the earth fault potential from within the premises.

 

[binky]

No it’s not 

Basically I’m struggling to understand why the installation guys run fly leads to unistrut when all its doing is supporting say an isolator. 

 I remember reading up on external lighting mounted on metal fencing some years ago, with no need to bond to the fence. Can't think where I read that, but think it may have been in a best practice guide or the ilk.

I did replace my garage roof with tin sheet roofing, I also have my solar panels mounted to that and the supporting framework for the roof is basically nice dry wood. This did allow an induced voltage to be maintained in the roof, so that has been bonded. 

 

[Jc1996]

Thanks guys I think I need to read up on  EN 60204-1:2018. Thats the thing that gets me we get sent on the wiring regs courses for my job as an industrial electrician. However alot of our equipment is machinery and I’m pretty sure the regs contradicts a few things in EN 60204-1:2018. Problem is me being fairly fresh out my time I want to know all these details but limited to what I can get out of the old school sparks on site. That’s probably where I will find the answer to fortuitous earthing. A lot of the old equipment I deal with exposed conductive parts are all earthed through a CPC and these exposed parts are then mounted on metal frames, is there really any point in bonding between these parts as well? An example is a slip ring assembly mounted to a rotating bridge