One of the thing that should be taken into consideration is external +24V specifications. In MS300, the STO circuit has an 8mA load for each channel so the total is 16mA. Number of total VFDs will depend on the 24V source. If internal +24V is used to provide the power to the safety relay, which is 100mA, then the maximum should be 6 units only (6x16mA).

Another thing to take into account is the feedback output MO. If you use several drives on one safety relay, those MO need to be connected in series. Please reach out to Delta IABG support for voltage drop calculations of MO.