Specifications

CHAPTER 3 INSTALLATION
3.3 Noise Countermeasures
14
3.3.4 Protective Measures against Lightning Surge
Generally, lightning surge infiltrates the control power supply from the power supply line. Then the
internal circuit is damaged by this control power supply, or via this control power supply.
The Mitsubishi NC unit has a surge absorber on the control power supply for the NC control section and
NC control section. However, this measure is not taken through the control panel, as shown in Fig. 1, so
the lightning surface could flow over the signal line and damage the other devices.
Power supply line
NC control
section
Power supply
for panel
NC drive section
(Servo, spindle
amplifier)
Control panel
(Relay panel,
etc.)
Lightning surge path
Fig. 1 Path of damage caused by lightning surge
(1) Methods of protective measures
Install the surge absorber on the power supply line for the separately prepared power supply units,
etc., as shown in Fig. 2 and Fig. 3.
The following two measures are required as protection against general damage.
1) Installation of surge absorber
2) Installation of circuit protector
Other device
(power supply
for panel, etc.)
Circuit
protector
Surge absorber (1)
Power supply line
Control panel
(Relay panel,
etc.)
Fig. 2 Lightning surge measures for single-phase power supply line
Other device
(power supply
for panel, etc.)
Circuit
protector
Surge absorber (3)Surge absorber (2)
Power supply line
Control panel
(Relay panel,
etc.)
Fig. 3 Lightning surge measures for 3-phase power supply line