Apple Power Macintosh 8500/120 Series - Manual (Page 158)

Expansion card power requirements
The combined power consumption of expansion cards must not exceed the
limits specified for your Macintosh model. If you have more than one
expansion card installed, check the information that came with your cards to
make sure that their power consumption is within the limits specified in the
Technical Information booklet.
Card installation
1 Turn off the computer.
Leave the computer plugged in to ground it and protect its components from
static electricity damage.
2 Loosen the four large screws at the corners of the back panel.
Do not completely remove the screws or the back panel.
146 Appendix B