VYPER
™
VARIABLE SPEED DRIVE
INSTALLATION
100.200-IOM (SEP 13)
Page 13
VFD APPLICATIONS
The primary ground conductor that accompanies the three-
phase supply must be stranded copper, insulated and two
sizes larger than the minimum required by the NEC or any
other applicable codes. This is necessary due to the increased
generation of EMI which is a characteristic of a VFD output
to the motor when compared to a conventional starter.
For VFD applications, isolation of the control power, analog
devices, and communications ground from the 3-phase
ground within the starter and the electronic control panel may
be necessary. This is due to the higher noise (RFI/EMI) levels
generated between the VFD output and the motor, relative
to a conventional starter. If these grounds are left coupled
by a common back-plate in the starter/drive, this noise can
be direct coupled to the control power, analog device, and
communications grounding and may cause unexplained
behavior and possible damage to components.
To install correctly, run a separate, properly sized (10 or 8
AWG typically) insulated ground along with and taken to
ground with, the 3-phase ground at the 3-phase supply
transformer (plant). This will require that the 3-phase ground
and the control power ground be electrically isolated except
for the connection at the plant supply transformer.
This style of grounding should steer the noise (EMI/RFI)
to earth ground, reducing the potential for it to affect the
sensitive equipment, which could occur if the grounds were
left coupled.
NOTICE
If all other recommendations for grounding are followed,
this process should not be necessary.
CONDUIT
All national and local codes must be followed for conduit
with regard to materials, spacing and grounding. In addition,
Johnson Controls-Frick requirements must be followed
where they exceed or match national or local codes. Con-
versely, there is no allowance for any practices that are
substandard to what is required by national or local codes.
Johnson Controls-Frick conduit requirements:
• For
variable frequency drives (VFDs) of any type, threaded
metallic or threaded PVC-coated metallic is required for
both the power feed (line side) from the source and be-
tween the VFD output and the motor (load side).
• PVC conduit is acceptable only when VFD rated cable of
the proper conductor size and ground is used. This applies
to both the line side and load side of the drive. When VFD
rated cable is not used, threaded metallic or threaded
PVC-coated metallic must be used.
• When threaded metallic or threaded PVC-coated metallic
is used, it must be grounded at both ends.
• When not required to be in metal or other material by na
-
tional or local codes, conduits for the power feed (3-phase)
of constant speed starters may be PVC.
• When not required to be in metal or other material by
national or local codes, conduits between a constant speed
starter and the motor (3-phase) may be PVC.
• Any unshielded control voltage, signal, analog, or com
-
munication wiring that does not maintain 12 inches of
separation from any 3-phase conductors for every 33 feet
(10 meters) of parallel run must be in metal conduit which
will be grounded.
Separation: (0-33 feet, 0-10 meters – 12 inches, .3 meters),
(33-66 feet, 10-20 meters – 24 inches, .6 meters)
• Since PVC conduit does absolutely nothing to protect lower
voltage lines from the
magnetic field effects of higher
voltage conductors, running either the lower or the higher
voltage lines in PVC, does not reduce these requirements
on separation. Only running in metal conduit can relieve
these requirements.
• Due to the level of EMI that can be induced onto lower volt
-
age lines when running multiple feeders in a trench, control
power, communications, analog, or signal wiring cannot
be run in trenches that house multiple conduits/electrical
ducts carrying 3-phase power to starters/vfd or motors.
• Control power, communications, analog, or signal wiring
should be run overhead (preferred) or in a separate trench.
If these lines are not in threaded metallic or threaded PVC-
coated metallic, abiding by the separation requirements
noted above is necessary.
• Though not recommended, if
cable trays are used, metal-
lic dividers must be used for separation of conductors of
unlike voltages and types (AC or DC).
NOTICE
When in doubt contact the factory or use threaded
metallic or threaded PVC coated metallic conduit.
WIRING PRACTICES
Do not mix wires of different voltages in the same conduit.
An example of this would be the installation of a screw
compressor package where the motor voltage is 480 volts
and the electronic control panel power is 120 volts. The 480
volt circuit must be run from the motor starter to the motor
in its own conduit. The 120 volt circuit must be run from the
motor starter control transformer to the electronic control
panel in its own separate conduit. If the two circuits are run
in the same conduit, transients on the 480 volt circuit will be
induced onto the 120 volt circuit causing functional problems
with the electronic control panel. Metallic dividers must be
used in wire way systems (conduit trays) to separate unlike
voltages. The same rule applies for 120 volt wires and 220
volt wires. Also, never run low voltage wires for DC analog
devices or serial communications in the same conduit with
any AC wiring including 120 volt wires. See Figure 8.
Figure 8 - Run Wiring Correctly