Published: January 2024
Recent changes to the BS7671 UK Wiring Regulations 18th Edition in the form of amendment 2 have introduced requirements and considerations for surge protection on both the AC and DC side of a solar PV System. Surge protection is an interesting topic and amendment 2 to the 18th edition wiring regulations introduces some of the most significant technical changes that we've seen in recent years. In this article we take a look at surge protection, particularly in the context of the updated UK wiring regulations and how surge protection could best be incorporated into new and existing solar PV systems installed in the UK.
Section 443 of BS7671:2018+A2:2022 is concerned with the AC (mains) side of the PV system and requires us to consider providing protection from transient overvoltages of an atmospheric origin or due to switching. Protection from overvoltage should be provided under the following circumstances:
The Surge Protection device (SPD) protecting the solar inverter must be within 10m of the inverter, if this can't be achieved at the incoming mains/grid supply meterering point or the source of the circuit, then an additional SPD should be installed close to the solar inverter. The regulation is summarised by stating that in all other cases a Surge Protection Device (SPD) shall be provided unless the owner of the installation declines such protection. A transient overvoltage is classed as a 10% (or more) spike in voltage over the distribution network's nominal value over a number of cycles. Of an atmospheric origin would apply to direct and indirect lightening strikes to equipment and cables on the mains power network. Damage to power lines and transformers on the mains network as well as re-energising after an outage could also be a cause of a spike in mains voltage. Section 712 of BS7671 is dedicated to solar PV systems and states that if a surge protection device is required under section 443 (the mains/AC side of the PV system) then surge protection will also be required on the DC side. |
Surge protection devices (SPDs) generate equipotential bonding between the connected conductors when excessive voltage is applied. This prevents voltage peaks from destroying connected devices. A surge protector will attempt to limit the voltage available to electrical devices over a safe threshold by either blocking excess voltage or shorting it to ground. There is a wide range of surge protection devices available of varying price and performance. The right device for each situation will be based on what a surge protection might be required to do in terms of it's clamping voltage, energy absorbtion and dissapation capabilities as well as it's response time. A Type 1 SPD is for use alongside Lightning Protection Systems (LPS) and for overhead mains power supplies A type 2 SPD is for use for installations not needing a type 1 SPD Type 3 SPDs are for sensitive equipment and installations such as fire alarm / burgalar alarm panels and are supplementary to Type 1 and 2 SPDs |
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Lots of articles, calculators and technical information including links for further reading. Covering a range of topics related to the installation and maintenance of solar photovoltaic and electrical systems in the UK.
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