Protective Earth Conductor
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.
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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 (mm^{2}) | Min. PE Conductor (mm^{2}) |
---|---|
0.5 | 0.5 |
0.75 | 0.75 |
1 | 1 |
1.5 | 1.5 |
2.5 | 2.5 |
4 | 4 |
6 | 6 |
10 | 10 |
16 | 16 |
26 | 16 |
35 | 16 |
50 | 25 |
70 | 35 |
95 | 50 |
120 | 70 |
150 | 95 |
185 | 95 |
240 | 120 |
300 | 150 |
400 | 240 |
500 | 300 |
630 | 400 |
800 | 400 |
1000 | 500 |
For protective earth conductors that are not of the same material as the phase conductors, a factor [math]\frac{k_1}{k_2} [/math] must be applied to the minimum size PE conductor in the table above.
The numerator [math]k_{1} [/math] is the k value for the phase conductors and the denominator [math]k_{2} [/math] 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):
- [math] A = \frac{\sqrt{i^{2}t}}{k} \, [/math]
Where [math]A \,[/math] is the minimum cross-sectional area of the PE conductor ([math]mm^{2}[/math])
- [math]i^{2}t \,[/math] is the energy of the short circuit ([math]A^{2}s[/math])
- [math]k \,[/math] is a constant term (this article has guidance for selecting the constant term)