8 - Equipotential bonding

Last edit: 03/03/2023

Chapter 8 of the Standard provides requirements for Protective bonding and Functional bonding. Protective bonding is a basic provision for fault protection to enable protection of persons against electric shock.

The objective of functional bonding is to reduce: 
–    The consequence of an insulation failure which could affect the operation of the machine; 
–    Electrical disturbances to sensitive electrical equipment which could affect the operation of the machine; 
–    Induced currents from lightning which could damage the electric equipment.

Functional bonding is achieved by connection to the protective bonding circuits, but where the level of electrical disturbances on the protective bonding circuit is not sufficiently low for proper functioning of electrical equipment, it can be necessary to use a dedicated terminal for protective and one for functional bonding. 

The protective bonding circuit, described in paragraph 8.2, consists of the interconnection of: 
–    PE terminals;
–    The protective conductors in the equipment of the machine; 
–    The conductive structural parts and exposed conductive parts of the electrical equipment. That means some metal parts of the machine can be used as protective bonding, even if we do not recommend it!

The Standard adds that it is not necessary to connect exposed conductive parts to the protective bonding circuit where those parts are mounted so that they do not constitute a hazard because: 

–    They cannot be touched on large surfaces or grasped with the hand and they are small in size (50 mm x 50 mm); or
–    They are located so that either contact with live parts, or an insulation failure, is unlikely. 

This applies to small parts such as screws, rivets, and nameplates and to parts inside an enclosure, irrespective of their size. 

In the 2021 Amendment to IEC 60204-1, it was clarified that "conductive structural parts of the machine" shall not be bonded, unless they are extraneous conductive parts. Therefore, please avoid doing like in the picture at the beginning of the page!