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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. However, if problems are encountered, the following guidelines may prove useful. In particular,
grounding of the system 0V at the inverter, as described below, may prove effective. Figure 1.2.1- 3 illustrates
how an RFI suppression filter should be installed.
(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 inverters should be connected directly to the earth
connection (PE) on the associated inverter.
(2)
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.
(3)
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.
(4)
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.
(5)
Use screened or armoured cables for the motor connections and ground the screen at both ends via
the cable glands.
(6)
If the drive is to be operated in an Electromagnetically noisy 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.
(7)
For FSA units (Fig 1.2.1), the flat earth braid strap, supplied with the unit, should be fitted to minimise
emissions .
On no account must safety regulations be compromised when installing inverters!
G85139-H1750-U049-C1
19/08/99
6
1. OVERVIEW
© Siemens plc 1999
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