What amazes me here is the complete lack of electrical knowledge in this
When I did my PV course and this came up, and the tutor said yes you bond back to the MET unless it is PM-E, which it wouldn't be, but I let it pass it is TNC-S in the installation, when it is TNC-S you stake it .................what!!!!
Why ........because the DTI say so....ahhhhhh so if you had a stainless steel boiler flue that could be touched while also touching the frame, that flue is obviously connected to the boiler, pipework is connected back to the MET via main equipotential bonding, and you then bond your frame to an earth stake ................how safe is that when you have 2 potentials within touching distance on the roof ...................blank stares we shall move on
I have yet been given an answer to this, though I know what will happen, if you had a fault within the installation and you were in contact with both potentials..................
Again this is another of these belt and braces decisions by someone, who believes that because it is a TNC-S system, there is a danger of a lost neutral, so it is do it this way and there is less risk, rather than doing what is right and having the competent electrician design and install what is the correct installation.
I have no problem if the DTi want us to bond to a stake if there is a TNC-S system, providing that TNC-S is not on a roof already .................but I would rather them say regarding bonding that the qualified, competent designer should assess each installation as he sees it, and with the information given by the manufacturer, design, install and test an installation suitable for conditions, but then I'm assuming to much perhaps.