Mitsubishi Electric PUHY-HP72 Service Handbook page 23

[1-4 Precautions for Wiring ]
2) Check the wires are securely fastened to the screw terminals.
Screw the screws straight down so as not to damage the screw threads.
Hold the two round terminals back to back to ensure that the screw will screw down straight.
After tightening the screw, mark a line through the screw head, washer, and terminals with a permanent marker.
Example
Mark a line.
Poor contact caused by loose screws may result in overheating and fire.
Continued use of the damaged circuit board may cause overheating and fire.
12 -
chapter 1
Daisy-chain
Power wires, transmission lines, centralized transmission lines
Place the round terminals back to back.
Power supply terminal block, indoor-outdoor transmission line terminal block,
and centralized controller transmission line
HWE18240_GB