4-28
4-3 Wiring Conforming to EMC Directives
4
System Design
Surge Suppressors
Install surge suppressors for loads that have induction coils, such as relays, solenoids, brakes,
clutches, etc.
The following table shows the types of surge suppressors and recommended products.
Note Thyristors and varistors are made by the following companies. Refer to manufacturers’
documentation for details on these components.
Thyristors: Ishizuka Electronics Co.
Varistors: Ishizuka Electronics Co., Matsushita Electric Industrial Co.
Contactors
Select contactors based on the circuit's inrush current and the maximum momentary phase
current.
The Servo Drive inrush current is covered in the preceding explanation of no-fuse breaker
selection, and the maximum momentary phase current is approximately twice of the rated current.
We recommend that you install two contactors to help prevent accidents that may occur due to
contact welding or other factors.
Type Features Recommended products
Diode
Diodes are used for relatively small loads
when the reset time is not an issue, such as
relays.
At power shutoff, the surge voltage is the
lowest, but the reset time becomes longer.
Used for 24/48-VDC systems.
Use a fast-recovery diode with a short
reverse recovery time
(e.g., RU2 of Sanken Electric Co., Ltd.).
Thyristor or
varistor
Thyristors and varistors are used for loads
when induction coils are large, as in electro-
magnetic brakes, solenoids, etc., and when
reset time is an issue. The surge voltage at
power shutoff is approximately 1.5 times
the varistor voltage.
Select the varistor voltage as follows:
24 VDC system: Varistor V0 39 V
100 VDC system: Varistor V0 200 V
100 VAC system: Varistor V0 270 V
200 VAC system: Varistor V0 470 V
Capacitor
+ resistor
The capacitor and resistor dissipate and ab-
sorb the surge at power shutoff. The reset
time can be shortened by selecting the ap-
propriate capacitor and resistance values.
Okaya Electric Industries Co., Ltd.
XEB12002 0.2 µF - 120 Ω
XEB12003 0.3 µF - 120 Ω
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