The system power supplies connect to the LocalBus to provide 12 VDC power to I/O cards. The number of system power supplies is determined by the total power required by the I/O cards and the redundancy scheme used by the application. To size the system power supplies, calculate the 12 VDC load by taking the sum of the LocalBus current for all cards connected to a set of 8-Wide I/O Carriers. Divide this total by 8 A to determine the number of supplies needed. The current requirements are listed in the table DC Current requirements for S-series I/O. If the total LocalBus current exceeds 15 A, you must inject additional power to the LocalBus.