Grounding The Drive; Ungrounded Distribution System; Input Power Conditioning - Baldor VS1SD Installation & Operating Manual

4.1 Grounding the Drive

Baldor does not recommend using "Grounded Leg Delta" transformer power leads that may create ground loops. Instead
we recommend using a four wire Wye. Baldor drives are designed to be powered from standard three phase lines that are
electrically symmetrical with respect to ground. System grounding is an important step in the overall installation to prevent
problems. The recommended grounding method is shown in Figure 4-1.
See recommended tightening torques in Table A-2.
Note: A line reactor is recommended
and must be purchased separately.
AC Main
Supply
Safety
Four Wire
Ground
Wye
Driven Earth
Ground Rod
(Plant Ground)
Route all 4 wires T1, T2, T3 and Motor Ground together

4.1.1 Ungrounded Distribution System

With an ungrounded power distribution system it is possible to have a continuous current path to ground through the MOV
devices internal to the VS1SD. To avoid equipment damage, an isolation transformer with a WYE grounded secondary is
recommended. This provides three phase AC power that is symmetrical with respect to ground.

4.1.2 Input Power Conditioning

Baldor drives are designed for direct connection to standard three phase lines that are electrically symmetrical with respect
to ground. An AC line reactor or an isolation transformer may be required for some power conditions.
• If the feeder or branch circuit that provides power to the drive has permanently connected power factor correction
capacitors, an input AC line reactor or an isolation transformer must be connected between the power factor correction
capacitors and the drive.
• If the feeder or branch circuit that provides power to the drive has power factor correction capacitors that are switched on
line and off line, the capacitors must not be switched while the drive is connected to the AC power line. If the capacitors
must be switched while the drive is connected to the AC power line, additional protection is required. TVSS (Transient
Voltage Surge Suppressor) of the proper rating must be installed on the drive input between the drive and any type of
input impedance such as an input reactor or drive isolation transformer.
MN766
Figure 4-1 Recommended System Grounding
L1
Optional
L2
Line
Reactor
L3
Earth
Route all 4 wires L1, L2, L3 and Earth (Ground)
together in conduit or shielded cable.
in conduit or shielded cable.
Connect all wires (including motor ground)
inside the motor terminal box.
TH1
Drive
TH2
GND
L1 L2 L3 T1 T2 T3
Optional
Load
Reactor
Chapter 4
Power Wiring
Note: Motor thermal leads must be run
in separate conduit from motor
power leads.
Note:
Wiring shown for clarity of
grounding method only. Not
representative of actual
terminal block arrangement.
Note: An optional separately
purchased load reactor
is recommended.
Ground per NEC and
Local codes.
Power Wiring 4-1