Operating & Mounting instructions – 8 074 143.03/03 – Page 70
Remarks on power supply
Mains impedance
Virtually all frequency inverters produce harmonic oscillation when connected to the mains, which
can interfere with other devices due to the voltage distortions thus caused.
Please note that all converters with connected intermediate circuit voltage (diode rectifier at input)
are a load on the mains supply in their total output. The use of a line choke (integrated in the CE-
DR filter) is therefore highly recommended, even when using an industrial supply network.
It is absolutely necessary if: • the mains symmetry can be >3%
• the output of the upstream transformer is ≥ 500 kVA
• there are strong mains voltage drops
• the inverter is operated on a generator
• the inverter is used in residential areas
• several inverters connected via a short bus bar
are supplied by the mains network
Without a line choke, the above operating conditions can cause damage to the inverter!!
Safety remarks / FI safety switch
Frequency inverters, particularly those with CE filters (RFI filters) and screened motor cables, conduct
an increased leakage current to earth. This depends on:
• the length of the motor cable
• the type of installation and whether the motor cable is screened or not
• the set clock frequency
• the use of a radio interference suppression filters (yes or no)
• the grounding of the motor on location (grounded or not)
Especially at the moment of switching on the filter's capacitors and during operation, the earth capa-
cities can lead to an unwanted FI safety switch trip. On the other hand, it is possible to block this trip
function through mains rectification at the input of the inverter with d.c. components.
Therefore, please note the following:
• Use only short-time delayed and clock-sensitive FI safety switches with considerably higher rated
trip current.
• Protect other consumers with a separate FI safety switch.
• FI safety switches upstream from a inverter are not an absolute safeguard against direct
contact!! Therefore, they should always be used in conjunction with other protective measures.
• The >pDRIVE< CX frequency inverters do not have a current-limiting effect (with fault currents),
and thus do not violate the grounding conditions.
In plants with cables of medium length, the leakage current can easily be greater than 300 mA,
depending on the conditions!!
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