Grounding is safety. Even in multi-storey buildings of the last century, a clever grounding system was used (about grounding systems more described in detail in chapter 1.7.3 of the PUE), in order to protect the residents of apartments in case of, for example, an unexpected breakdown on body. How to properly ground, and, the main question: what section should you buy a protective conductor? Further in the article.
Which wire to choose for the ground line
If the wiring is done from scratch, then you should not conduct a separate cable - it can be included in the common conductor, as an additional conductor to the existing phase and null. This means that any cable in the apartment must be three-core: "phase", "zero" and "earth".
A separate paragraph in the PUE is devoted to PE-conductors or grounding wires.
And clause 1.7.121. clearly says that:
- The ground wire can be routed together with the phase conductor.
- Both insulated and non-insulated PE conductors can be used.
Third subclause 1.7.121
. states that the grounding conductor can be laid permanently, as many electrical companies are doing now, which is quite justified.Calculation of the cross-section of the grounding conductor
Many electricians do not really understand the essence of the issue and always purchase a cable with conductors of the same cross section. As a result, the "ground" wire does not differ from the phase or working "zero". But PUE provides for the smallest dimensions of grounding conductors and are entered in the form of formulas in a separate table.
Basic formulas for determining the smallest section of a PE conductor:
- For phase cross-section S ≤ 16 mm2, cross-section of PE conductor: S.
- With phase cross section 16
- With phase cross-section S> 35, cross-section of PE-conductor: S / 2.
It should be immediately clarified that such calculations are performed only at serious industrial enterprises, and during the laying of electrical wiring in scrap or apartments, they are very often neglected.
What is the cross-section of a separately laid PE conductor
This issue is detailed in paragraph 1.7.127. PUE, which states that the cross-section of a separately laid grounding wire, if it has additional mechanical protection, must be at least 2.5 mm2. If such protection is not provided, then the cross-section is increased to 4 mm2, depending on the purpose of the cable. It is best to use only copper conductors for grounding.
Also, a few words about the marking of PE conductors, which is regulated by clause 1.1.29 of the PUE: ground wires can be marked with both longitudinal and transverse yellow-green stripes. GOST R 50462-92 prohibits the use of this indication with any other meaning. Clause 1.7.118 there is also an identification mark, which can now be purchased at almost any hardware store or electrical store.
The above information is relevant only for networks with voltages up to 1000 V. Above 1 kV, the parameters of protective conductors are completely different.