
B-63003EN-2/01 Chapter 1 Assembling the 16i/18i/21i 1 - 37
1
Grounding the 16i/18i/21i Machine Tool Control System
The control system must be properly grounded. The following three ground systems are
provided for the CNC machine tool (see Figure 1-19 below):
1
.
The signal ground system supplies the reference voltage (0V) of the electrical signal
system.
2
.
The frame ground system is used for safety and suppressing electrical noise. In this
system, the frames, cases of the units, panels, and shields for the interface cables
between the units are connected.
3
.
The system ground system is used to connect all of the separate frame ground systems
to a common ground.
Figure 1 - 19. Block diagram of proper grounding
Keep the following things in mind when connecting the ground systems:
• Connect the signal ground to the frame ground at only one place in the CNC control
unit.
• The resistance of the system ground must be 100 ohms or less (class 3 grounding).
• The system ground cable must have enough cross-sectional area to safely carry the
fault current into the system ground when an accident occurs. Typically, it must have
the cross sectional area of the AC power cable or more.
• For the operator’s panel and the machine, use the ground wire in the AC power cord.
Signal grounding system
Frame grounding system
System grounding syste
Distribution board
24V DC
power
Power
magnetics
unit
Servo amp control
Machine
tool
Operator’s
panel