
6.INSTALLATION CONDITIONS AND NOTES SVM B-65322EN/02
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6.2 SELECTING A GROUND-FAULT CIRCUIT INTERRUPTER
Because the servo amplifier βi series uses the PWM inverter system
by transistors to drive a motor, high frequency leakage current flows
via the motor winding, power cable, and amplifier floating capacity to
ground. This may cause the ground-fault circuit interrupter or
ground-fault protective relay installed on the power supply side to
malfunction.
Therefore, when using a circuit breaker with a ground-fault circuit
interrupter, select an appropriate one having an inoperative current
value not smaller than the sum of the calculation results (a) and (b) to
prevent malfunctioning due to leakage current.
(a) Selection criterion per amplifier
Selection criterion: 2 mA per amplifier(*1)
(b) Selection criterion per motor
Selection criterion: 1 mA per motor(*1)
The following example shows how to use selection criteria <1> and
<2>:
Example:
When the system contains four βi SVM1 units
2 mA × 4 units (amplifiers) + 1 mA × 4 (motors) = 12 mA
→ Select a circuit breaker with an inoperative current of 12
mA or more(*2).
(A general ground-fault circuit interrupt applicable to this
example has a rated sensitivity current of 30 mA, and an
inoperative current of 15 mA.)
NOTE
1 The above selection criteria are provided in order
to select a circuit breaker with a ground-fault circuit
interrupter, and do not express accurate leakage
current values.
2 Depending on the frequency characteristic of the
ground-fault circuit interrupter, the circuit breaker
may malfunction. So, use a ground-fault circuit
interrupter usable for inverter circuits.
3 The above selection criteria are values in the
commercial frequency band. Some instruments
measuring leakage current may detect a high
frequency band and read larger values.
WARNING
Install a ground-fault circuit breaker.
To prevent fire and electric shock to a person, be
sure to install a ground-fault circuit breaker (for
inverter circuits).