Last edit: 09/05/2023
Currently the NEC in Article 100 defines the terms "ground" or "grounded" as "connected to the earth or to some conducting body that serves in place of the earth." Yet, the NEC often uses the term "ground" when it really means "bond" (connected to an effective ground-fault path to clear a fault) [250.2 and 250.4(A)(5)]. The two concepts have quite a different meaning.
Grounding – Grounding metal parts to earth in premises wiring is only useful to provide a path for lightning, shunting high-frequency noise, or reducing static discharge.
Bonding – Bonding all metal parts together and then to the system winding is done to provide a low-impedance path to the source ( TN system) to facilitate the opening of the circuit-protection device to remove dangerous voltage on metal parts. In addition, bonding the system to metal parts stabilizes the system voltage and it provides a zero system reference.
So far it is all clear, those are the definitions. The question now is what to be connected to Ground and what pieces of equipment should be bonded together.
The approach of the Noth American Techical standards (mainly NEC and NFPA 79) is unfortunately a bit different from the IEC EN 60204-1 and that makes the subject more complex since at the end the risk of electric shock is the same for a worker in UK or in USA.
So why two different approaches? Both approaches recognise the need for a ground fault path, and that is the main reason for bonding. The real difference is the concept of Class II electrical devices or apparatus that is in the EN 60204-1 but that cannot be found the National Electrical code or in the NFPA 79.
Enough for the theory: if you need a good training for your electrical engineers, you may give us a call, even for a chat on the subject.