3.5.4. Extra Protection (RCD)
ELCB relays, multiple protective grounding or grounding can be used as extra protection, provided
that local safety regulations are complied with.
In the case of a ground fault, a DC content may develop in the faulty current.
If ELCB relays are used, local regulations must be observed. Relays must be suitable for protection
of 3-phase equipment with a bridge rectifier and for a brief discharge on power-up.
See also the section
Special Conditions
in the relevant Design Guide.
3.5.5. RFI Switch
Line supply isolated from ground
If the adjustable frequency drive is supplied from an isolated line power source (IT line power,
floating delta and grounded delta) or TT/TN-S line power with grounded leg, it is recommended
that the RFI switch be turned off (OFF)
1)
via par. 14-50. For further reference, see IEC 364-3. If
optimum EMC performance is needed, parallel motors are connected or the motor cable length is
above 82 ft [25 m], it is recommended to set par. 14-50 to [ON].
1)
Not required with 525-600/690 V drives; therefore not possible.
In OFF, the internal RFI capacities (filter capacitors) between the chassis and the intermediate
circuit are cut off to avoid damage to the intermediate circuit and to reduce the ground capacity
currents (according to IEC 61800-3).
Please also refer to the application note
VLT on IT line power
, MN.90.CX.02. It is important to use
isolation monitors that are capable of being used with power electronics (IEC 61557-8).
3.5.6. Torque
When tightening all electrical connections, it is
very important to tighten with the correct tor-
que. Too low or too high torque results in a
bad electrical connection. Use a torque
wrench to ensure correct torque.
3.79: Always use a torque wrench to tighten the
bolts.
3. How to Install
VLT
®
Automation Drive FC 300
Instruction Manual High Power
56
MG.33.U1.22 - VLT
®
is a registered Danfoss trademark.
3
