Renewable sources of electricity and the 17th Edition of the IEE Wiring Regulations (BS 7671:2008) -

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18/02/2009

THE SCOPE of the 17th Edition is wider and contains many new requirements, including additional requirements to ensure the safe connection of low-voltage generating sets including small scale embedded generators and solar photovoltaic (PV) power supply systems. In this article we look at the new Regulations in Section 551 and Section 712.

Chapter 55 – Other Equipment. Regulation 551 – Low Voltage Generation Sets

This set of Regulations now includes additional requirements contained in Regulation 551.2 to ensure the safe connection of low-voltage generating sets including small scale embedded generators.

A new Regulation, 551.4.2, regarding the use of RCDs, has been added. Regulation 551.4.2 states:

The generating set shall be connected so that any provision within the installation for protection by RCDs in accordance with Chapter 41 remains effective for every intended combination of sources of supply.

Notes have been added including one to Regulation 551.1 stating that the procedure for connecting generating sets up to 16 A in parallel with the public supply is given in The Electricity Safety, Quality and Continuity (Amendment) Regulations 2006. For sets above 16 A the requirements of the distributor must be ascertained. The 17th Edition recognises that there are two connection options:

(i) Connection into a separate dedicated circuit
(ii) Connection into an existing final circuit

Connection into a dedicated circuit is preferred. Regulation 551.7.2 sets out the requirements for the two options. The Regulation requires that a generating set used as an additional source of supply in parallel with another source shall either be installed on the supply side of all protective devices for the final circuits of the installation (connection into a separate dedicated circuit) or if connected on the load side of all protective devices for the final circuits must fulfil a number of additional requirements.

These additional requirements are:

(i) the current carrying capacity of the final circuit conductors shall be greater than or equal to the rated current of the protective device plus the rated output of the generating set, and
(ii) A generating set shall not be connected to a final circuit by a plug and socket, and
(iii) A residual current device providing additional protection of the final circuit in accordance with Regulation 415.1 shall disconnect all live conductors including the neutral conductor, and
(iv) The line and neutral conductors of the final circuit and of the generating
set shall not be connected to earth, and
(v) Unless the device providing automatic disconnection of the final circuit in accordance with Regulation 411.3.2 disconnects the line and neutral conductors, it shall be verified that the combination of the disconnection time of the protective device for the final circuit and the time taken for the output voltage of the generating set to reduce to 50 V or less is not greater than the disconnection time required by Regulation 411.3.2 for a final circuit.

PV Installation

Section 712 of BS 7671:2008 is concerned with the safe installation of solar photovoltaic (PV) power supply systems. A PV system is a collection of interconnected PV cells that turn sunlight directly into electrical energy.

The risks

Modules produce electricity when exposed to daylight. This needs to be taken into account during design, installation, use and maintenance. Also, the electrical installation which incorporates a PV system has a second source of energy which needs to be isolated before starting work. A further risk involves working at height on a roof for example together with the manual handling associated with a PV installation. Finally, PV installations require expertise in dc wiring and fault protection for d.c. side of the installation.

Scope

Section 712 of BS 7671:2008 applies to the electrical installations of PV power supply systems including systems with a.c. modules. Section 712 does not apply to PV power supply systems which are intended for standalone operation.

The Electricity Safety, Quality and Continuity (Amendment) Regulations 2006

Solar photovoltaic (PV) power supply systems are required to meet the Electricity Safety, Quality and Continuity (Amendment) Regulations 2006 (ESQCR) as they are embedded generators. These are mandatory requirements.

However, where the output does not exceed 16 A per line they are smallscale embedded generators (SSEG) and are exempted from certain of the requirements provided that:

(i) the equipment should be type tested and approved by a recognised body,
(ii) the consumer’s installation should comply with the requirements of BS 7671,
(iii) the equipment must disconnect itself from the distributor’s network in the event of a network fault, and
(iv) the distributor must be advised of the installation before or at the time of
commissioning.

See Engineering Recommendations G83/1, for PV systems up to 16A (5kw) and G59/1, published by the Energy Networks Association (ENA)* for larger systems and generators, etc.* Further information can be obtained at the ENA's website: www.ena-eng.org/