Star Point Earthing - Parker AC890 Product Manual

Screening & Earthing
Note The installation requirements of local safety standards must be achieved regarding the safety of
electrical equipment for machines.. Refer to Chapter 4: Connecting Power.
The VSD, external filter and associated equipment are mounted onto a conducting, metal mounting panel.
Do not use cubicle constructions that use insulating mounting panels or undefined mounting structures.
Cables between the VSD and motor must be screened or armoured and terminated at the VSD or locally on
the back panel.

Star Point Earthing

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
890SD (Standalone) Drive: Frame G, H & J
Certification
Page C-13