Eurotherm Drives 584S, Product Manual, Page: 60 / 176

CHAPTER 3 - INSTALLATION PROCEDURE
3-18 584S FREQUENCY INVERTER
locally but this will not cause shielding problems due to the relatively high RF impedance of the local earth
connection.
AC
Supply
Filter
Motor Cable Screen
Motor
Safety
Earth
PE
PE
PE
AC/DC
PE
As short
as possible
Figure 3-6: Screening and earthing of a single 584S/620 drive module.
When more than one piece of electrical equipment is fitted inside an enclosure, care must be taken to ensure that
noise flowing in the earth connection does not couple into other equipment. A star-point earthing policy separating
noisy from quiet earths is strongly recommended. Five separate earths branches should be provided for:
♦
Clean earth busbar
The Clean earth busbar is used as a reference point for all signal and control cabling. This
may the further subdivided into an analogue and a digital reference busbar, each separately
connected to the star earthing point. The digital reference is also used for any 24V control.
♦
Dirty earth busbar
The dirty earth busbar is used for all power earths (i.e. protective earth connections)
♦
Enclosure metalwork
busbar
The enclosure metalwork busbar is used for all parts of the cubicle including panels, doors
and back plate. It is also used as a reference for any 110 or 220V control used and for the
control transformer screen.
♦
Power screen busbar
The power screen busbar is only for power screened cables which do not have to go
directly to the 584S/620 drive module (such as motor cables, braking choppers and their
resistors) or to other drive modules (refer to appropriate Product Manual to identify these).
Noise coupled onto the incoming screens must flow to earth directly so as not to
contaminate the rest of the cubicle. Hence the power screen busbar should be placed as
close to the point of cable entry as possible.
♦
Signal/control screen
busbar
The signal/control screen busbar is to be used for signal/control screened cables which do
not have to go directly to the 584S/620 drive module. This busbar should also be placed as
close as to the point of cable entry as possible.
For optimum EMC performance, copper rails with a substantial cross-section should be used for the busbar.
Screened cables are best ‘u’ clamped to the busbars to ensure an optimum HF connection.
The five separate earth busbars should be insulated from the mounting panel and connected to a single earth point
(star point) near the PE or PEN terminal of the main supply. Flexible large cross-section cable to ensure a low HF
impedance should be used. The arrangement of the busbars should be such that the connection to the single earth
point are as short as possible. Figure 3-7 shows an implementation of a star-point earthing policy.
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