PUE-6 (1985), Section 1.7 Earthing and safety — clause by clause

Clause-by-clause review of PUE-6 (1985) section 1.7: TN-C neutral bonding ("zanulenie"), 4 Ω earth resistance, no RCDs in housing — and how it differs from PUE-7.

Document

Document	PUE-6 (1985), Section 1.7 Earthing and safety
Edition	1985 (ПУЭ-6)
Status	Historical (chapters not replaced by PUE-7 remained until the 2000s)
Issued by	Ministry of Energy of the USSR
Applies to	Earthing and safety in installations up to 1 kV, 1985 edition

Document structure

№	Chapter / section
1.7.1–1.7.17	Scope, systems
1.7.18–1.7.33	Earthing and neutral bonding
1.7.34–1.7.60	Earthing arrangements
1.7.61–1.7.90	Protective conductors

Earthing system (1.7.1–1.7.17)

PUE-6 used the old terminology: protective earthing, neutral bonding (zanulenie — TN-C predecessor) and protective disconnection.

1.7.2 Neutral bonding (TN-C) was the standard for LV networks with earthed neutral: PEN served as both neutral and protection.

1.7.5 RCDs only as a supplement in special cases.

Resistance and electrodes (1.7.18–1.7.60)

1.7.24 Earth resistance ≤ 4 Ω at 380/220 V (10 Ω below 100 kVA) — kept in PUE-7.

1.7.53 Earthing conductors: steel 100 mm² in soil, copper 25 mm², aluminium 35 mm².

Differences from PUE-7

• Terminology: "zanulenie" instead of TN systems; TN/TT/IT classification appeared only in PUE-7;
• RCDs: not required for housing in PUE-6; 30/10 mA RCDs became mandatory in PUE-7;
• Bathrooms: bonding in bathrooms not mandatory in PUE-6, mandatory in PUE-7 (1.7.92);
• N-PE prohibition (1.7.135) — only in PUE-7;
• PEN split rules — only in PUE-7.

Practical takeaways

PUE-6 legacy is millions of TN-C flats. Modernization: 30 mA RCDs, PEN split in the intake, supplementary bonding in bathrooms (per PUE-7 and SP 256).

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