Rockwell Automation Publication 7000L-UM301F-EN-P - March 2020
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Drive Installation
Chapter 2
Identification of Types of Electrical Supplies – Grounded and
Ungrounded Systems
When dealing with an ungrounded, three-phase electrical supply system, the
cable insulation must be capable of handling not only the phase-to-phase voltage,
but also the voltage-to-ground if one of the other phases develops a ground fault.
In practice, the cable insulation of an ungrounded, three-phase system must be
good for at least a continuous voltage of root three (1.732) times (1.1) times the
rated voltage of the supply. (1.732 x 1.1 = 1.9 times the rated line-to-line voltage)
Ground Bus
The drive ground bus runs along the top of the drive at the front. The ground bus
is accessible at the top of each of the drive enclosures when the enclosure door is
opened (and the low voltage compartment hinged out in the case of the incomer
cabinet). It is the responsibility of the installer to ensure that the drive is
grounded properly, typically at the point on the ground bus in the incomer
cabinet, close to the incoming power terminations.
Interlocking
Access to the medium voltage areas of the drive is restricted by the use of key
interlocking for safety.
At installation the key interlocking is set up so that access to the medium voltage
compartments of the equipment can only be made when the upstream power is
locked in the off position.
Additionally, the key interlocking prohibits the upstream power being applied
until the medium voltage drive’s access doors have been closed and locked shut.
It is the responsibility of the installer to ensure that the key interlocking is
installed properly to the upstream equipment.
