The British Standard BS 7671, also known as the IET Wiring Regulations, sets out the requirements for electrical installations in the UK. When it comes to plug-in solar systems, there is a potential conflict with BS 7671 concerning the use of plug sockets for connecting micro-generation equipment like solar panels.

BS 7671 requires that all electrical installations, including those for micro-generation, must be safe and not present any risk of injury or fire. The use of standard plug sockets for connecting solar panels or micro-inverters is generally not recommended because these sockets are not designed for continuous use at the full rated current, which solar panels can generate under certain conditions. This could potentially lead to overheating and fire risks¹.

Moreover, BS 7671:2018+A2:2022 has introduced changes in surge protection requirements, which could affect plug-in solar installations. Surge protective devices (SPDs) are now required where the consequence caused by overvoltage could result in serious injury, loss of life, failure of a safety service, or significant financial or data loss. For all other cases, SPDs should be fitted unless the installation owner declines such protection¹.

Therefore, it’s crucial for plug-in solar systems to comply with these regulations to ensure safety and legality.

The IET Wiring Regulations, specifically BS 7671, cover the requirements for generators connected to final circuits in several sections. Here are some relevant parts:

• Regulation 411.3.3: This regulation discusses the use of RCDs (Residual Current Devices) and their exceptions, particularly when a generator is supplying a distribution unit that has 30 mA RCDs protecting final circuits¹.
• Chapter 53: This chapter includes regulations such as 531.3.2, which highlights the use of RCBOs (Residual Current Circuit Breaker with Overcurrent protection) for individual final circuits in residential premises to minimize unwanted tripping, and 531.3.3, which states that RCD Type AC shall only be used to serve fixed equipment where it is known that the load current contains no DC components².
• Regulation 421.1.7: This regulation has been redrafted to require the protection of final circuits supplying socket-outlets with a rated current not exceeding 32 A using arc fault detection devices (AFDD) in specific types of buildings³.

These sections ensure that the connection of generators to final circuits is done safely and in compliance with the latest safety standards, do take a read....
The next part is the connection location, which would generally apply to any generation source/s.

In electrical systems, the terms “upstream” and “downstream” refer to the flow of electricity from the source to the load. When discussing circuits with multiple sources of energy input, these terms help to identify the direction in which power flows and how it is managed.

Upstream Circuits: These are closer to the energy sources and handle the initial distribution of power. In a system with multiple sources, such as a grid-connected solar panel setup, the upstream circuit would include the connections at the utility scale or the point where the solar panels connect to the inverter. Upstream circuits must be capable of managing the combined input from all sources and ensuring stable distribution.

Downstream Circuits: These circuits are further along the power distribution path, closer to the end-use applications or loads. They receive power that has been managed and distributed by the upstream circuits. In a home with solar panels, the downstream circuit would be the internal wiring that delivers electricity to outlets and appliances.

With multiple sources of energy input, such as solar and wind combined with grid power, there are additional considerations:

• Energy Management: Systems must be in place to prioritize and manage the different energy inputs, often using smart meters and management systems.
• Safety and Protection: Proper protection mechanisms, like surge protectors and circuit breakers, are essential to handle the variable nature of renewable energy sources.
• Regulation Compliance: The system must comply with local regulations for connecting to the grid and managing multiple energy sources.

When connecting solar photovoltaic (PV) systems to an existing electrical installation, the solar system can be considered an additional power source. This means that parts of the installation that were originally downstream circuits may become upstream in relation to the solar input. This shift necessitates specific protection requirements to ensure safety and compliance with electrical codes.

Protection Requirements:

• Overcurrent Protection: The sum of 125 percent of the power source’s output circuit current and the rating of the overcurrent device protecting the busbar should not exceed the ampacity of the busbar¹.
• Disconnect Placement: A PV system disconnect must isolate the components that convert solar energy into electric energy. The location of the disconnect is crucial to ensure that all downstream equipment operates properly without the power source².
• Surge Protection: According to regulations, PV installations must be protected by surge protection devices (SPDs) on both the AC and DC sides to handle different degrees and types of protection³.

see attached diagram for solar protection using SPD