Functional Earthing Conductor (FE): Definition, Example, Color and Symbol

Functional earthing conductor (UK, IEC) or functional grounding conductor (US): conductor provided for functional earthing [defined in the IEC 60050-195-2021].

Functional earthing conductor
Figure 1 – Main earthing terminal connecting the earthing conductor to installation protective conductors. The figure shows the functional earthing conductor

Some electronic equipment requires a reference voltage at about earth potential in order to function correctly; this reference voltage is provided by the functional earthing conductor.

Conductors for functional earthing may be metallic strips, flat braids and cables with circular cross section.

For equipment operating at high frequencies, metallic strips or flat braids are preferred and the connections shall be kept as short as possible.

For equipment operating at low frequencies, cross sectional areas as indicated in 544.1.1 of IEC 60364-5-54 are considered satisfactory, independent of the conductor shape; see 444.4.2 b) and k) IEC 60364-4-44.

All protective and functional earthing conductors of an installation within a building shall be connected to the main earthing terminal, except where this is precluded by the requirements of legislation or Part 7 BS 7671.

The requirements for functional earthing shall be defined by the manufacturer or the relevant product committee and should be specified within the documentation of the equipment.

Functional Earthing Conductor (FE) Example

Where there are problems in existing building installations due to electromagnetic influences, the following measures may improve the situation; see Figure 2:

1 ) use of metal free fibre optic links for signal and data circuits, see 444.4.9 [3];
2) use of Class II equipment;
3) use of double winding transformers in compliance with IEC 61558-2-1 or IEC 61558-2-4 or IEC 61558-2-6 or IEC 61558-2-15. The secondary circuit should preferably be connected as a TN-S system but an IT-system may be used where required for specific applications.

Illustration of measures in an existing building
Figure – 2 Illustration of measures in an existing building [3]. The figure shows the functional earthing conductor
ReferenceDescription of the illustrated measures
1)Cables and metal pipes enter the building at the same place
2)Common route with adequate separations and avoidance of loops
3)Bonding leads as short as possible, and use of earthed conductor parallel to a cable
4)Signal cables screened and/or conductors twisted pairs
5)Avoidance of TN-C beyond the incoming supply point
6)Use of transformers with separate windings
7)Local horizontal bonding system
8)Use of class II equipment

Color and Alphanumeric Identification

A functional earthing conductor shall be identified by the colour PINK. It is only necessary to apply the identification at the terminations and at points of connection.

In Australia, the colour PINK is the preferred colour for identification of a functional earthing conductor (“FE”) , but the colour WHITE is also accepted.

In UK, the colour Cream is the preferred colour for identification of a functional earthing conductor (“FE”) [Table 51, BS 7671].

Functional earthing conductor colour and alphanumeric notation

Note g. Neither the designation FE nor the graphical symbol 5018 of IEC 60417 shall be applied for electrical conductors or terminals having a protective function. Bi-colour insulation GREEN-AND-YELLOW shall not be used for conductors that do not have a protective function (i.e. for conductors other than PE, PEN, PEL, PEM, PB, PBE, PBU).

The alphanumeric identification of a functional earthing conductor shall be “FE”.

References

  1. IEC 60050-195-2021
  2. BS 7671
  3. IEC 60364-4-44
  4. IEC 60364-5-54