BS 7671 Section 712 Guide for UK Solar PV Electrical Installations

Key Takeaways

• Section 712 of the IET Wiring Regulations (British Standard 7671) establishes specialised safety rules for solar photovoltaic power supply systems.
• Under statutory Regulation 4 of the Electricity at Work Regulations 1989, all electrical systems must be constructed and maintained to prevent danger.
• Regulation 5 of the 1989 Regulations prohibits putting electrical equipment into use where its strength and capability may be exceeded.
• DC switchgear must be rated to break full load current under maximum open-circuit array voltage and short-circuit current conditions.
• For energy storage pairings, PAS 63100 defines fire safety benchmarks for domestic systems within low-voltage boundaries defined in BS 7671.
• Responsible persons under the Fire Safety Order 2005 must implement general fire precautions to ensure workplace installations remain safe.

The Scope of BS 7671 Section 712

Photovoltaic generators operate under unique electrical conditions: solar arrays produce continuous direct current (DC) that cannot be switched off during daylight hours, creating sustained arc hazards and elevated thermal risks. Section 712 of British Standard 7671 provides dedicated technical requirements for the design, selection, and erection of PV arrays, inverters, and isolation switchgear.

The standard covers the entire DC installation—from string connections behind the modules to the DC input terminals of the inverter—and interfaces with AC distribution boards.

Statutory Safety Principles: the 1989 Electricity at Work Regulations Regulations 4 and 5

Every installation complying with Section 712 is anchored in statutory law under the Electricity at Work Regulations 1989:

Construction and Maintenance (Regulation 4)

Regulation 4 sets absolute legal obligations for electrical systems:

• All systems shall at all times be of such construction as to prevent, so far as is reasonably practicable, danger.
• As may be necessary to prevent danger, all systems shall be maintained so as to prevent, so far as is reasonably practicable, such danger.
• Every work activity, including operation, use and maintenance of a system and work near a system, shall be carried out in such a manner as not to give rise, so far as is reasonably practicable, to danger.
• Any equipment provided under these Regulations for the purpose of protecting persons at work on or near electrical equipment shall be suitable for the use for which it is provided, be maintained in a condition suitable for that use, and be properly used.

Strength and Capability (Regulation 5)

A critical rule for DC switchgear selection is enshrined in Regulation 5:

• No electrical equipment shall be put into use where its strength and capability may be exceeded in such a way as may give rise to danger.
• In solar PV systems, DC disconnectors, string cables, and fuses must be rated for maximum prospective array voltage (adjusted for lowest expected ambient temperatures) and maximum reverse currents.

Domestic Storage Integration: PAS 63100 Interface

Where a solar installation is paired with battery storage in a domestic property, installers must integrate Section 712 principles with the British Standards Institution fast-track specification PAS 63100:2024.

PAS 63100 defines fire safety requirements for the installation of BESS components including:

1. Physical requirements for battery units.
2. Battery management systems (BMS).
3. Power conversion equipment (PCE).
4. Fault management and fail-to-safe operation of all control and monitoring functions.

The scope of PAS 63100 is explicitly aligned with standard wiring regulations, excluding battery systems with nominal voltages on the AC and/or DC side exceeding low voltage as defined in BS 7671.

Furthermore, Historic England guidance on solar panels has been updated to include advice on mitigating the risk of fire and protecting historic structures.

Commercial Installations and the Fire Safety Order 2005

For non-domestic solar installations on commercial roofs and industrial premises, electrical compliance interfaces with the Regulatory Reform (Fire Safety) Order 2005.

Under Article 8 of the Order, the responsible person must:

• Take such general fire precautions as will ensure, so far as is reasonably practicable, the safety of any of his employees.
• In relation to relevant persons who are not his employees, take such general fire precautions as may reasonably be required in the circumstances of the case to ensure that the premises are safe.