AC and DC Surge Protection is a topic that is gaining more and more momentum within the Solar PV installation sector. Sibert is pleased to be able to support a wide range of surge protective devices (SPDs) manufactured by our partner Dehn (www.dehn.co.uk).
Protection of the DC circuits, the Inverter and downstream AC circuits is imperative in the event of a direct and/or induced surge, regardless of whether the PV array is bonded or not. Several different scenarios exist regarding the level of protection required dependent on the nature of the existing electrical grid supply and the presence (or not) of any existing lightning protection system (LPS).
Recent changes to the BS7671 wiring regulations help to clarify the requirements for any required SPD installation and a copy of the ammendment can be downloaded from the linked files below for further information.
Starting with the DC-side, there are typically 3 different types of installation, the most common being a non-grounded or double-insulated system. Adding a surge device here will mean fitting Type-2 SPDs to protect against indirect strikes.
The next type of installation would be one where a lightning protection system (LPS) is already fitted to the roof. This installation is mindful of the need for adequate separation distance from the copper tapes of the LPS and the frame of the Solar PV modules. In this case the DC circuits are protected with Type-2 SPDs but as there is an LPS on the roof, the AC circuit needs to be protected by a Type-1 SPD.
Lastly, the 3rd typical installation type is where there is already a pre-fitted LPS on the roof but the modules are fitted without adequate consideration of the required separation distance from the LPS so flash-over to the frame of the Solar PV modules is possible. In this instance, both the AC and DC circuits need to be protected by Type-1 SPDs.
SPDs are available as DIN-rail mountable units on their own, or pre-configured inside custom designed enclosures.
Surge Protection 17th Edition, Amendment 1 - BS 7671
DEHN Redline Selection Guide - BS 7671 Am. 1 Consequences
DEHN Protects - PV Systems
DEHN Surge & Fire Protection
DEHN PV Flyer