Digitax ST User Guide
7
Issue: 5
1.11.4 Stored charge
The drive contains capacitors that remain charged to a potentially lethal
voltage after the AC supply has been disconnected. If the drive has been
energized, the AC supply must be isolated at least ten minutes before
work may continue.
Normally, the capacitors are discharged by an internal resistor. Under
certain, unusual fault conditions, it is possible that the capacitors may fail
to discharge, or be prevented from being discharged by a voltage
applied to the output terminals. If the drive has failed in a manner that
causes the display to go blank immediately, it is possible the capacitors
will not be discharged. In this case, consult Emerson Industrial
Automation or their authorized distributor.
1.11.5 Equipment supplied by plug and socket
Special attention must be given if the drive is installed in equipment
which is connected to the AC supply by a plug and socket. The AC
supply terminals of the drive are connected to the internal capacitors
through rectifier diodes which are not intended to give safety isolation. If
the plug terminals can be touched when the plug is disconnected from
the socket, a means of automatically isolating the plug from the drive
must be used (e.g. a latching relay).
1.11.6 Permanent magnet motors
Permanent magnet motors generate electrical power if they are rotated,
even when the supply to the drive is disconnected. If that happens then
the drive will become energized through its motor terminals.
If the motor load is capable of rotating the motor when the supply is
disconnected, then the motor must be isolated from the drive before
gaining access to any live parts.
