Earthing for metal frame surrounding outside lights?

[GettingOnWithItAll]

My house has a 2.5m x 5m wooden lean-to down the side between the house side wall and side fence. It has lighting on the rafters run off a 5A circuit breaker in a small CU situated in a utility room in the 1930s main house but accessed by an external door (it was the coal storage room); this CU has a 40A RCD run off a dedicated CB in the main CU supplying the gas boiler, sockets and lighting to the utility room. AFAIK the system is TNS.

The side by the fence has racking that I want to enclose. The doors I have are heavy. I have spare steel angle and tubing that I could weld together to make a metal frame to help support the doors and roof beams, allowing me to move the existing support posts. The frame would enclose some of the outside lights and run close to some of the wiring (enclosed in plastic conduit).

If I make the frame rather than use wood, would it be advisable to bond it to the main house earth? If so, would it be better to do so directly to the light supply or to, say, the existing bonding to the water pipes in the utility room and would any regulations get in the way of my doing the bonding?

Thanks in advance for any help.

 

[ericmark]

Personally I would not earth it to a TN-C-S and you can never be sure if a TN-S will be made TN-C-S without your knowledge, if earthed to TN-C-S and there is a fault, then metal work could become live. So I would rely on the RCD to disconnect under fault conditions.

As to what the regs say not so easy, I am sure some one will quote chapter and verse.

 

[flameport]

Is the frame an extraneous conductive part?