Protective Earth Conductor
From Open Electrical
The protective earth (PE) conductor is defined as a conductor that is provided for safety purposes (e.g. against the risk of electric shock) and which also provides a conductive path to earth. The PE conductor can be integrated inside a multi-core cable (e.g. 3C+E cable) or can be a separate cable.
Minimum Protective Earth Conductor Size
The protective earth conductor should be sized so that during a fault, it will be able to withstand the prospective fault current. IEC 60364-5-54 provides two options for the sizing of protective earth conductors.
Sizing from a Table
For protective earth conductors constructed of the same material as the phase conductors, the minimum size for protective earth conductors are as follows:
|Phase Conductor (mm2)||Min. PE Conductor (mm2)|
For protective earth conductors that are not of the same material as the phase conductors, a factor must be applied to the minimum size PE conductor in the table above.
The numerator k1 is the k value for the phase conductors and the denominator k2 is the k value for the PE conductor. Calculation of the k values are described on this page.
Sizing by Calculation
As per Clause 543.1.2 of IEC 60463-5-54, the size of protective earth conductors can be calculated by the adiabatic short circuit temperature rise equation (for disconnection times <5s):
Where is the minimum cross-sectional area of the PE conductor (mm2)
- is the energy of the short circuit (A2s)
- is a constant term (this article has guidance for selecting the constant term)