In many facilities it is beneficial to insure that the multiple welders in a station not fire at the same time to prevent a sudden large draw on the plant power supply. To spread this out cascade controls can be employed where one control will sequence through several contactors in sequence. The sequence and separation between the welds can be controlled to give an appropriate modest draw on the power supply.
In centralized networks this function can be controlled by the central PLC and the initiation command is sent to each weld control or robot station to fire in sequence.
Reference: ENTRON Controls LLC