• In drives with frequency converters, leakage currents occur along the RFI filter and the cable capacities,
especially during the motor start. Class A leakage detection protections would switch off the machine.
Therefore it is not recommended to use class A detection systems on frequency converters.
Installation instructions for TN, TT, IT
In each network system (TN, TT or IT), the customer has to protect the installation using overcurrent protection
by means of fuses or automatic circuit breaker protection.
With respect to the power distribution system, additional installation instructions are given.
Network type TN (TN-S, TN-C and TN-C-S)
No additional protections need to be installed. If the customer wishes to or needs to install a leakage detection
device, it should be of type B and should comply with IEC755 Amendment 2 "General requirements for
residual current-operated protective devices". Atlas Copco advises customers to install the following earth
leakage detection device: BENDER RCMA 470LY with external current transformer: http://www.bender.org/
prod.html
Network type TT
In the case of TT-systems, safety regulations mostly stipulate the use of an earth leakage circuit breaker
(e.l.c.b). In combination with frequency converters, type B residual current-operated protective devices should
be used. Atlas Copco advises customers to install the following earth leakage detection device: BENDER
RCMA 470LY with external current transformer: http://www.bender.org/prod.html
Network type IT
In IT-network systems, it is permissible for the power supply to continue in the event of an initial earth leakage
fault of a motor phase. However, the customer must detect the initial earth leakage fault. The fault must be
indicated as an alarm. If this is not the case, the initial earth leakage fault must trigger automatic disconnection
of the power supply (EN 60204-1 par.: 6.3). However, the high frequency capacitive leakage currents caused
by frequency converters cannot be detected by standard earth leakage detection systems. Atlas Copco
recommends that customers install: BENDER IRDH 275/435 http://www.bender.org/prod.html.
Atlas Copco strongly recommends that customers do not connect the neutral conductor from the power supply
to the compressor unit. The exposed conductive parts of the installation must be earthed locally. (EN 60204-1
par.: 7.2.3)
Power distribution systems (TN, TT, IT)
According to IEC 60950, there are three main types of power distribution systems: TN, TT and IT. The
electrical installation instructions depend on the type of network of the customer's power supply.
Network type TN (Terra Neutral) :
The TN power distribution system provides a direct earth to the exposed conductive parts of the installation.
The connection is made through the PEN-conductor. Within the TN power distribution system, there are three
sub-types: TN-S, TN-C and TN-C-S, identified according to neutral and protective earth conductors. Nearly
85 % to 90 % of industrial networks are TN type.
Network type TN-S (Terra Neutral-Separate) :
The TN-S power distribution system provides separate neutral and direct earth conductors.
Instruction book
92 2920 1728 05
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