Let’s have a look at a real world situation.
A simple one really but let’s have a look at some of the Wiring Regulations that may apply.
A three story steel scaffold is being built on the outside of a building to complete some renovation work. There will be walkways and working gantries and as it’s all sheeted off from the public it will be lit by temporary lighting. The workforce will be using power tools and will need supplies for this. The building is supplied using a TN-C-S earthing system.
Does the steel scaffold need bonding to the main earthing system of the building?
The first place to look is in…
Part 7: Section 704 Construction and Demolition Site Installations
You’ll see from 704.1.1 (ii) that this section applies to this installation.
Also as we are going to supply the lights and any power tools from the building then Regulation 704.411.3.1 will apply. This states that a PME earthing facility shall not be used unless all extraneous conductive parts are connected to the main earth terminal.
Is the scaffold an extraneous conductive part? See Part 2: Definitions
So in short ‘Yes’ and see Regulation 544.1.1 for the size of the main protective bonding conductor, for a TN-C-S look at Table 54.8 usually supply neutral <35mm so 10mm would suffice in this instance. Other things to consider would also be in Section 704... 704.41 (i) 'reduced low voltage' 110v protection against electric shock re hand held electrical equipment. 704.52 Wiring systems - re cable positioning and type used for the lighting and power supplies. All based upon information in the current 17th Edition of the IET Wiring Regulations BS7671:2008+A3:2015 - The 'yellow' book.