English 1. OVERVIEW
G85139-H1751-U529-D1 © Siemens plc 199
4/8/99
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1.2 Wiring Guidelines to Minimise the Effects of EMI
The inverters are designed to operate in an industrial environment where a high level of Electro-Magnetic Interference (EMI) can be
expected. Usually, good installation practices will ensure safe and trouble-free operation. If problems are encountered, the following
guidelines may prove useful. In particular, grounding of the system at the inverter, as described below, may prove effective. Figures
1.2.1-1.2.3 illustrate how an RFI suppression filter should be installed and connected to the MICROMASTER Vector.
(1) Ensure that all equipment in the cubicle is well earthed using short, thick earthing cable connected to a common star point or
busbar. It is particularly important that any control equipment that is connected to the inverter (such as a PLC) is connected
to the same earth or star point as the inverter via a short, thick link. Flat conductors (e.g. braids or metal brackets) are
preferred as they have lower impedance at high frequencies.
The return earth from motors controlled by the inverter should be connected directly to the earth connection (PE) on the
associated inverter.
(2) On the MIDIMASTER Vector, use saw-tooth washers when mounting the inverter and ensure that a good electrical
connection is made between the heatsink and the panel, removing paint if necessary.
(3) Wherever possible, use screened leads for connections to the control circuitry. Terminate the ends of the cable neatly,
ensuring that unscreened wires are as short as possible. Use cable glands whenever possible.
(4) Separate the control cables from the power connections as much as possible, using separate trunking, etc. If control and
power cables cross, arrange the cables so that they cross at 90° if possible.
(5) Ensure that contactors in the cubicle are suppressed, either with R-C suppressors for AC contactors or ‘flywheel’ diodes for
DC contactors, fitted to the coils. Varistor suppressors are also effective. This is particularly important if the contactors are
controlled from the relay on the inverter.
(6) Use screened or armoured cables for the motor connections and ground the screen at both ends via the cable glands.
(7) If the drive is to be operated in an Electro-magnetic noise-sensitive environment, the RFI filter should be used to reduce the
conducted and radiated interference from the inverter. For optimum performance, there should be a good conductive bond
between filter and metal mounting plate.
(8) For Frame Size A units (Fig.1.2.1), the flat earth braid strap, supplied with the unit, should be fitted to minimise emissions.
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