How will AMD2 affect surge protection for solar installations | Surge Protection Devices

How will AMD2 affect surge protection for solar installations | Surge Protection Devices

Amendment 2 has provided a number of proposed changes around surge protection, with significant changes to section 712 which discusses the regulations surrounding solar photovoltaic (PV) power supply systems. Kirsty Johnson, Technical Sales Director at Surge Protection Devices, looks at how these might work.

New regulation 712.443.101 states that where protection against transient overvoltage is required by section 443, such protection shall also be applied to the DC side of the PV installation. So, if for example, the solar installation is on the roof of an industrial building where the regulations in section 443 require SPDs to be installed, SPDs would now also need to be installed on the DC side of the installation to protect both the PV panels and the inverter.

When a PV system is installed within the protected volume of the LPS system, the PV system should be separated from all parts of the LPS in accordance with BSEN 62305-3, which describes the calculation for the correct separation distance. If the separation distance isn’t met, then to BSEN 62305 a Type 1 device will be needed to protect the installation from the effects of lightning.

All SPDs installed on the DC side of a PV installation shall comply with BSEN 61643-31. When the inverter incorporates an SPD, it’s only considered as fulfilling the SPD requirement if the manufacturer specifies its use for the DC side of the PV installation, otherwise it will need an external SPD. Varistors included in the inverter aren’t considered an SPD.

Generally, the SPD will be a Type 2, unless the building has an external lightning protection system. If the LPS doesn’t have the correct separation distance according to BSEN 62305-3, a Type 1 device will be required.

On selection of the SPD for the PV system, care must be taken to ensure that the following guidelines are met:

  • The Up of the SPD must not exceed the Uw of the equipment to be protected (if you don’t have this information, table 712.1 in BS7671 will provide average ratings)
  • The Ucpv should be greater than or equal to the Uoc max of the PV array
  • Type 2 SPDs should have a minimum In of 5kA
  • Type 1 SPDs should have a minimum Iimp of 12.5kA


Fig 1


Fig 2

Where the inverter is located more than 10m away from the origin of the installation, an SPD shall be installed near the inverter, in addition to the SPD at the origin of the installation. The type of device will depend on the installation. The illustration in Fig 2 will help to determine what is required.

SPDs on the DC side shall be located as close as possible to the inverter, and to provide protection additional SPDs may be required further from the inverter.

Fig 3 is recreated from BS IEC 61643-32. It details the locations required for SPDs on a PV installation.

AC side: The SPD at location 3 is the main incomer, which is required under BS 7671, section 443 or BSEN 62305, if an LPS system in present. If the SPD at location 3 is more than 10m from the PV inverter, an additional SPD should be installed at location 2. The type of this device can be decided using Fig 2.

DC side: If an SPD is located at location 3, then a DC SPD is required at location 1. The type can be decided using Fig 1. If the PV array is located more than 10m away from the SPD at location 1, then an additional SPD can be installed at location 4 to provide local protection for the PV array.

Obviously, at the time of writing we’re working with the ‘proposed’ changes and there is a chance that some elements may have changed slightly by publication. We’re currently expecting publication of Amendment 2 in March 2022, which we all know will be here before we know it!

Fig 3


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