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YORK INTERNATIONAL16
FIG. 3 – CONTROL INSTALLATION
LD06727
Grounding
Grounding is the most important factor for successful
operation. Electronic equipment reacts to very small
currents and must have a good ground in order to
operate properly. The NEC states that control equipment
may be grounded by using the rigid conduit as a
conductor. This is not acceptable for electronic control
equipment. Conduit is a poor conductor compared
to a copper wire. Copper grounds are required for
proper operation.
Ground Wire Size (Figure 4)
The ground wire must be the same size as the supply
wires or one size smaller as a minimum. The three
phase power brought into the plant must also have a
ground wire, making a total of four wires. In many
installations that are having electronic control problems,
this essential wire is usually missing. A good ground
circuit must be continuous from the plant source
transformer to the electronic control panel for proper
operation. Driving a ground stake at the electronic
control will cause additional problems since other
equipment in the plant on the same circuits will ground
themselves to the ground stake causing large ground
ow at the electronic equipment.
LD06728
FIG 4 – GROUNDING
Wiring Practices (Figure 5)
Do not mix wires of different voltages in conduit. For
an example refer to Figure 5. The motor voltage is 480
volts and the panel control 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 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 inducted into the 120 volt
circuit causing functional problems with the electronic
control. 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 in the same conduit
with 120 volt wires.
Never run any wires through an electronic control
panel that do not relate to the function of the panel.
Electronic 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.
When running conduit to an electronic control panel,
note that the access holes (knockouts) are strategically
placed so that the eld wiring does not interfere with
the electronics in the panel. Never allow eld wiring to
come in close proximity with the controller boards
since this will almost always cause problems.
Installation