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Electrical Contract Works · Question
Short answer
Earthing is a deliberate low-resistance connection between an installation's metal parts and the ground, so that a fault sends current along a safe path instead of through a person. It is tested carefully because an earthing system that looks fine can still fail to do its job, and the failure only shows up on the day a fault occurs.
When insulation fails or a cable touches a metal body, that body can become live. Earthing gives the fault current an easy route to the ground, which lets protective devices detect the problem and cut the supply quickly. It also keeps exposed metal parts, such as machine frames and panel doors, at a safe potential relative to the floor beneath a person's feet.
For a new installation the earthing arrangement is part of the design, and the qualified electrical contractor builds it to the applicable codes and local requirements. The owner does not need to know the method. What an owner should know is what to expect and ask for.
An earth connection can be present on paper and still be poor in practice. Soil moisture, a loose joint, a corroded connection or a missing link can all weaken it, and none of these is visible from the surface. Testing by a competent person with proper instruments is the only way to confirm that the system performs as designed.
What to ask for:
Not a task for the owner
Earthing and its testing involve live installations and specialist instruments. Leave inspection, repair and modification to qualified professionals who work to applicable codes.
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This answer is general information, not advice on your particular case. Terms, eligibility, and requirements change, so check the current position with the relevant institution or authority.