PUE 7, Chapter 3.1 Protection of LV networks — clause by clause

Clause-by-clause review of PUE chapter 3.1: mandatory short-circuit and overload protection, breaker and fuse selection, breaking capacity, sensitivity, selectivity.

Document

Document	PUE 7, Chapter 3.1 Protection of LV networks
Edition	2002 (ПУЭ-7, гл. 3.1)
Status	Current
Issued by	Ministry of Energy of Russia
Applies to	Protection of networks up to 1 kV: protective device selection, selectivity

Document structure

№	Chapter / section
3.1.1–3.1.10	General requirements
3.1.11–3.1.25	Protective device selection
3.1.26–3.1.34	Placement of devices

General (3.1.1–3.1.10)

3.1.4 Networks need short-circuit and overload protection.

3.1.7 Breakers or fuses.

3.1.8 Breakers with combined (thermal + magnetic) trips.

3.1.10 Breaking capacity ≥ max fault current at the point.

Selection (3.1.11–3.1.25)

3.1.11 Rated current ≥ calculated, ≤ cable ampacity.

3.1.16 Sensitivity: fault current at line end ≥ 1.3 × trip current.

3.1.18 Overload protection may be omitted where overload is impossible.

3.1.24 Socket circuits: overload protection mandatory.

Selectivity (3.1.26–3.1.34)

3.1.26 Upstream/downstream devices coordinated (selectivity).

Practical takeaways

Chapter 3.1 justifies "16 A on 2.5 mm²" and "32 A on 6 mm²": In between calculated and cable ampacity (3.1.11), breaking capacity (3.1.10), 1.3× sensitivity (3.1.16), selectivity (3.1.26).

Data is for reference. Final design decisions must follow current regulations and a qualified engineer.
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