AT&T System 75 Wiring Diagram page 171

CHAPTER 3. EQUIPMENT ROOM DESIGN
If the approved ground or approved floor ground can only be
accessed inside a dedicated power equipment room, then
connections to this ground should be made by a licensed
electrician
TRUNK
CIRCUITS
SINGLE-POINT
GROUND BLOCK
Figure 3-59. Installing the Coupled Bonding Conductor
3-88
DANGER
10 GAUGE CBC
CABLE
ENTRANCE
TERMINAL
LIGHTNING
SURGE
PROTECTOR
APPROVED GROUND