070.610-IOM (JUL 21)
Page 19
RWF II Rotary Screw Compressor Units
Installation
Conduit
All national and local codes must be followed for conduit
with regard to materials, spacing and grounding. In addi
-
tion,
Johnson Controls-Frick requirements must be fol-
lowed where they exceed or match national or local codes.
Conversely, 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, thread
-
ed metallic or threaded PVC-coated metallic is required
for both the power feed (line side) from the source and
between 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 metal
-
lic is used, it must be grounded at both ends.
• When not required to be in metal or other material by
national or local codes, conduits for the power feed
(three-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 (three-phase) may be PVC.
• Any
unshielded control voltage, signal, analog, or com
-
munication wiring that does not maintain 12 inches of
separation from any three-phase conductors for every
33 feet (10 meters) of parallel run must be in metal con
-
duit which will be grounded.
Separatio
n:
Distance interval
Spacing
0 ft to 33 ft (0 m to 10 m)
12 in. (0.3 m)
33 ft to 66 ft (10 m to 20 m)
24 in. (0.6 m)
• Because 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 con
-
duit can relieve these requirements.
• Due to the level of EMI that can be induced onto lower
voltage 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 three-phase power to starters,
VFD, or motors.
• Control power, communications, analog, or signal wir
-
ing 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.
• Thou
gh not recommended, if cable trays are used, me-
tallic div
iders 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 V
and the electronic control panel power is 120 V. The
480 V circuit must be run from the motor starter to the
motor in its own conduit. The 120 V circuit must be run
from the motor starter control transformer to the elec-
tronic control panel in its own separate conduit. If the two
circuits are run in the same conduit, transients on the 480
V circuit will be induced onto the 120 V circuit causing
functional problems with the electronic control panel. Me-
tallic dividers must be used in wire way systems (conduit
trays) to separate unlike voltages. The same rule applies
for 120 V wires and 220 V wires. Also, never run low volt
-
age wires for DC analog devices or serial communications
in the same conduit with any AC wiring including 120 V
wires. See the following figure.
Figure 23: Separation of different voltage circuits
Never run any wires through an electronic control panel
that do not relate to the function of the panel.
Elec-
tronic control panels should never be used as a junction
box. These wires may be carrying large transients that
will interfere with the operation of the control panel.
An
extreme example of this would be to run 480 V from
the starter through the electronic control panel to an
oil pump motor.
When running conduit to the electronic control panel,
use the access holes (knockouts) provided by the manu
-
facturer. These holes are strategically placed so that the
field wiring does not interfere with the electronics in the
panel. Never allow field wiring to come in close proximity
with the controller boards because this will almost always
cause problems.
Do not drill into an electronic control panel to locate con-
duit connections. You are probably not entering the panel
where the manufacturer would like you to since most
manufacturers recommend or provide prepunched conduit
connections. You may also be negating the NEMA rating
of the enclosure. Drilling can cause metal filings to land on
the electronics and create a short circuit when powered
is applied. If you must drill the panel, take the following
precautions:
