As RF has already said, you don't need to "earth" the grid but many do for the reasons RF has stated. However, it's not black & white because in the event of an earth fault somewhere else in the installation you maybe introducing a problem that would not normally be there.
Also, if you do decided to "earth" the grid at one point you will need to test the whole grid to ensure you have continuity. Depending on the construction/type of grid you may well end up having to cross bond joints etc.
Although they are not always in the real world below is the NIC’s view
In practice, unless there are very exceptional circumstances (which would need to be taken into account by the electrical designer), the conductive parts of a suspended ceiling will be neither exposed-conductive-parts nor extraneous-conductive-parts. Consequently, in normal circumstances, suspended ceilings need neither to be earthed nor equipotentially bonded.
Electrical equipment such as luminaires, lighting track, overhead busbars, air conditioning units and the like incorporated in a suspended ceiling will normally be of either Class I or Class II construction. The exposed-conductive-parts of Class I equipment are required to be connected to the main earthing terminal of the installation by a circuit protective conductor designed to conduct earth fault current. Class II equipment is designed such that any insulation fault in the equipment cannot result in fault current flowing into any conductive parts with which the equipment may be in contact. The conductive parts of a suspended ceiling incorporating Class I and/or Class II equipment are therefore not intended to conduct earth fault current, and so such parts need not be intentionally earthed. (Some conductive parts of a suspended ceiling may be earthed, however, by virtue of fortuitous contact with exposed-conductive-parts, including those of Class I equipment.)
Unless there are exceptional circumstances, the conductive parts of a suspended ceiling will not introduce a potential that does not already exist in the space in which the ceiling is installed. In normal circumstances, therefore, there is no need to arrange for the conductive parts of the ceiling to be connected to either a main bonding conductor or to any supplementary bonding conductor.
Some of the requirements applicable to cables in suspended ceilings are embodied in Regulation Groups 522-06, 522-07 and 522-08 of BS 7671. In particular, Regulations 522-08-04 and 522-08-05 call for cables to be supported, either continuously or at appropriate intervals, such that no damage or undue strain will occur to the cables themselves or to their terminations.
It is inadvisable for cables, including insulated and sheathed cables to BS 6004, to be laid directly on a suspended ceiling grid for a number of reasons, including:
• The cables are liable to be damaged, both during installation and later, by the sharp edges of the grid (Regulations 522-06-01 and 522-08-01). For example, a cable may come into contact with the cut edges of the grid at a notch where sections of grid intersect, or may become trapped between a ceiling tile and the grid, possibly when other trades are carrying out work in connection with the ceiling or other services routed above.
• The suspended ceiling grid may not have been designed to take the additional weight of cables, and may deform or collapse as a result.
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