Chapter 54 of BS 7671 relates to earthing and bonding conductor selection and sizing.
There is confusion over earthing conductors, and main protective bonding conductors and which Regulation to refer to.
The definitions of each are as follows:
Earthing conductor: A protective conductor connecting the main earthing terminal of an installation to an earth electrode or to other means of earthing.
Protective Bonding Conductor: Protective conductor provided for protective equipotential bonding
The confusion arises in selection of sizing, so here are a couple of examples:
Earthing conductor - "Every earthing conductor shall comply with Section 543",
Section 543 states that:
The cross sectional area of every protective conductor, other than a protective bonding conductor, shall be:
(i) calculated in accordance with Reg. 543.1.3, (adiabatic equation)
(ii) selected in accordance with Regulation 543.1.4 (Table 54.7)
An example would be from Table 54.7:
If the CSA of the line conductor (S) is 25mm2, (16<S<35)
Then the protective conductor is to be 16mm2