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14
RCD
(FI-Protective
Switch)
If personnel protection is required during installation of the system the frequency
inverters must be protected according to EN 50178 (VDE 0160):
– 1-phase inverters by RCD type A (pulse-current sensitive FI’s) or type B (all-
current sensitive FI’s)
– 3-phase inverters (with B6 bridge-connected rectifier) by RCMA’s with
separation (used privileged) or RCD’s type B (all-current sensitive FI’s)
The tripping current should be 300mA or more, in order to avoid a premature
triggering of the inverter by discharge currents (about 200mA).
Dependent on the load, the length of the motor cable and the use of a radio
interference filter, substantially higher leakage current can occur.
The connection instructions from the manufacturer and the valid local reqirements
must be observed.
Dependent on the available mains form (TN, IT, TT) further protective measures
are necessary in accordance with VDE Part 410 (Part 4; Chapter 41). For example,
with TN-mains this protection is made with overcurrent protective devices. With
IT-mains it is insulation monitoring with a pulse-code measuring method. A
protective separation can be used with all mains forms as long as the required
power and cable lengths permit this.
Before starting, all respective enclosures must be secured again, as well as the
terminals and screws must be checked to see that they are securely fixed.
Inverters/servo drives may be set, dependent on type, to restart automatically
following a fault stoppage (e.g. Undervoltage Error), when the fault conditions
clear. System design must take this into account, if appropriate, and additional
monitoring or protective features added where necessary.
The frequency inverters/servo drives are conditionally short-circuit proof (EN
50178). After resetting the internal protection devices, the function as directed is
guaranteed.
Exceptions:
– If an earth-leakage fault or short-circuit often occurs at the output,
this can lead to a defect in the unit.
– If a short-circuit occurs during regenerative operation (2nd or 4th quadrant,
feedback into the intermediate circuit), this can lead to a defect in the unit.
2.5 Operating Instructions
Automatic
Restart
Conditionally
Short-Circuit
Proof