5.INSTALLATION B-65282EN/05
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5.1 LEAKAGE CURRENT
The servo amplifier αi series drives the motor by using the transistor
PWM inverter method. This causes a high-frequency leakage current
to flow via the ground drift capacitance in the motor winding, power
cable, and amplifier. This may cause a device installed on the power
supply side, such as a ground fault interrupter or leakage-protection
relay, to malfunction.
When a circuit breaker with a ground fault interrupter is used, it must
be selected so that the sum of the values calculated according to (a)
and (b) described below is not greater than the non-operating current
value.
(a) Selection criterion per amplifier
Model : SVM and SPM
Criterion for selection : 2 mA per amplifier (Note 1)
(b) Selection criterion per motor
Criterion for selection : 1 mA per motor (Note 1)
The following example shows how to use selection criteria (a) and
(b):
Example :
When the system consists of SMV1×1, SVM3×1 (three motors),
and SPM×1
2 mA×3 (for the amplifiers) + 1 mA×5 (for the motors) = 11 mA
→ Select a circuit breaker (Note 2) with a non-operating
current of 11 mA or higher. (A general ground fault
interrupter that can be used for the above example is the
one with a rated sensitivity current of 30 mA and a non-
operating current of 15 mA.)
NOTE
1 These criteria are for selecting a circuit breaker with
a ground fault interrupter; they do not indicate
accurate leakage currents.
2 A circuit breaker may malfunction depending on the
frequency characteristic of the ground fault
interrupter. Therefore, use a ground fault interrupter
supporting the use of inverters.
3 The above criteria are values in the commercial
frequency band. Some measuring instruments for
measuring leakage current may sense a high
frequency band, thus showing a larger value.