Last edit: 12/01/2024
Electrical Safety is well standardized, in the sense that there are many technical documents written on the Subject, normally by the International Electrotechnical Commission, or IEC.
The issue is that, being many people involved in the standardisation process, coordination among them is difficult and therefore not all standards are consistent among each other. That generates confusion.
The confusion is also generated by the fact that our North American Colleagues, sometimes, use the terms Bonding and Grounding as synonyms.
This article’s aim is to clarify the meaning of 6 important symbols.
The first part is about 3 important electrical functions: Isolation, Protection and Switching.
ISOLATION: it is a key concept in electrical Safety. Isolation ensures the protection of people performing electrical work.
[IEC 61140:2016] 3. Terms and definitions
3.41 isolation. function intended to disconnect and maintain for reasons of safety adequate clearance from every source of electric energy
This is the symbol for an Isolating device like a disconnector
PROTECTION: it is the protection of a line or of an electrical equipment from overload, short circuit and ground fault (indirect contacts or Fault Protection). It can be realised by a Circuit Breaker or a Fuse switch.
[IEC 60947-2:2016] 2. Terms and definitions
2.1 circuit-breaker. A mechanical switching device, capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specified time and breaking currents under specified abnormal circuit conditions such as those of short-circuit
The following is the symbol for a Circuit Breaker
SWITCHING DEVICE: it allows the energisation or de-energisation of a line. An example is a Power Contactor.
[IEC 60947-4-1] 3.3 Terms and definitions concerning contactors
3.3.1 (mechanical) contactor
mechanical switching device having only one position of rest, operated otherwise than by
hand, capable of making, carrying and breaking currents under normal circuit conditions
including operating overload conditions
The following is the symbol for a Power Contactor.
The last three symbols are related to the concept of Grounding and Bonding. Please remember that: Electrical Systems are Grounded, while Electrical Equipment are Bonded!
GROUNDING SYMBOL: It means that the conductive part is connected to the “Dirty ground”. A typical example is the neutral point of a MV/LV transformer to create a TN-S system. Grounding is the term used in USA and Canada. Earthing is the term used in most IEC standards.
[IEC 60364-5-54] 541.3 Terms and definitions
541.3.3 earth electrode
conductive part, which may be embedded in the soil or in a specific conductive medium, e.g.
concrete, in electrical contact with Earth
Hereafter the Symbol:
BONDING SYMBOL: It means the connection of an Exposed Conductive Part to the neutral point of a MV/LV transformer, as part of the electrical safety in a TN-S system.
[IEC 60364-4-41: 2017] 411.3 Requirements for fault protection
411.3.1.1 Protective earthing. Exposed-conductive-parts shall be connected to a protective conductor under the specific conditions for each type of system earthing as specified in 411.4 to 411.6. Simultaneously accessible exposed-conductive-parts shall be connected to the same earthing system individually, in groups or collectively. Conductors for protective earthing shall comply with IEC 60364-5-54. Each circuit shall have available a protective conductor connected to the relevant earthing terminal.
Hereafter the Symbol for Protective Earthing (PE): It can be attached to the terminal of an Exposed conductive part, where the Green/Yellow cable is connected.
Again: this is a symbol for BONDING and not for GROUNDING (EARTHING)!
BONDING OF EXTRANEOUR CONDUCTIVE PART SYMBOL: Extraneous Conductive Parts needs to be bonded.
[IEC 60364-4-41: 2017] 411.3 Requirements for fault protection
411.3.1.2 Protective equipotential bonding
In each building, incoming metallic parts which are liable to introduce a dangerous potential difference and do not form part of the electrical installation shall be connected to the main earthing terminal by protective bonding conductors; examples of such metallic parts may include:
- pipes supplying services into the building, for example gas, water, district heating systems;
- structural extraneous-conductive-parts;
- accessible reinforcement of constructional reinforced concrete.
Hereafter the Symbol for Protective equipotential Bonding (PB). It can be attached to the terminal of an Extraneous conductive part, where the Green/Yellow cable is connected.
