UPS Parallel Systems Joiner (PSJ)

A Parallel Systems Joiner (PSJ) is an output power coupling switch that enables two independent groups of UPS operating in parallel to join together. 

A PSJ performs a similar role to a UPG Group Synchronisers. It connects the outputs from two distinct groups of parallel UPS into a dynamic dual bus for system expansion, fault tolerance and ease of maintenance.  

If one of the UPS within the two parallel systems fails or needs to be switched off for maintenance and emergency service work, the PSJ merges the two outputs to allow power sharing.

By: https://www.riello-ups.com/questions/54-what-does-a-ups-parallel-systems-joiner-do