Rockwell Automation 1771-P4S_P6S_P4S1_P6S1 Power Supply Modules Installation Instructions - Manual (Page 10)

Publication 1771-IN079A-EN-P - June 2002
10 Allen-Bradley Power Supply Modules
Troubleshooting Parallel
Power Supplies If you have a pair of power supplies installed in parallel in the I/O chassis
and the P/S ACTIVE indicators are off, verify the ground connection to the
supply; then follow the flow chart below.