12-4
Certification for the Servo Drive
07-01-08-02-E-V0500 631 Digital Servo Drive
Star Point Earthing
Doors
Metal
Work
110V
Control
24V Control
unscreened signals
STAR POINT
Incoming Safety Earth (PE)
Analogue Clean Earth
Dirty Earth
Digital Clean Earth
Signal/Control Screen
all screened signals not
Back Panel
U-clip used to terminate screen
connection to the back panel
PE = Protective Earth
0A = 0 Volts Analogue
0D = 0 Volts Digital
f = External Filter
VSD = Variable Speed Drive
PLC = Programmable Logic Controller
going directly to a VSD
Metal Work Earth
Back
Panel
PLC
PE
PE
PE
0D
0D
0D
0D
0A
0A
0A
to motor
to motor
to motor
screened
screened
PE
VSD
VSD
VSD
f
f
f
f
PE
PE
PE
A star-point earthing policy separates `noisy’ and `clean’ earths. Four separate earth busbars
(three are insulated from the mounting panel) connect to a single earth point (star point) near the
incoming safety earth from the main supply. Flexible, large cross-section cable is used to ensure
a low HF impedance. Busbars are arranged so that connection to the single earth point is as short
as possible.
1 Clean Earth Busbar (insulated from the mounting panel)
Used as a reference point for all signal and control cabling. This may be further subdivided into
an analog and a digital reference busbar, each separately connected to the star earthing point.
The digital reference is also used for any 24V control.
2 Dirty Earth Busbar (insulated from the mounting panel)
Used for all power earths, i.e. protective earth connection. It is also used as a reference for any
110 or 220V control used, and for the control transformer screen.
3 Metal Work Earth Busbar
The back panel is used as this earth busbar, and should provide earthing points for all parts of the
cubicle including panels and doors. This busbar is also used for power screened cables which
terminate near to (10cm) or directly into a VSD - such as motor cables, braking choppers and
their resistors, or between VSDs - refer to the appropriate product manual to identify these. Use
U-clips to clamp the screened cables to the back panel to ensure optimim HF connection.
4 Signal/Control Screen Earth Busbar (insulated from the mounting panel)
Used for signal/control screened cables which
do not
go directly to the VSD. Place this busbar
as close as possible to the point of cable entry. `U’ clamp the screened cables to the busbars to
ensure an optimum HF connection.
