A power supply unit cannot on its own guarantee fault-free 24-V supply. Power failures, extreme variations in the mains voltage, or a faulty load can bring plant operation to a standstill and cause high costs. The easy-to-integrate expansion modules offer everything from reliable protection against interference on the primary and secondary side, right up to complete all-round protection. The add-on modules allow flexible expansion of SITOP power supplies towards a complete all-round protection.