York 00497VIP manual Grounding, Ground Wire Size Figure, Wiring Practices Figure

Installation

equipment in the plant on the same circuits will ground themselves to the ground stake causing large ground flow at the electronic equipment.

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FIG. 3 – CONTROL INSTALLATION

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

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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 field wiring does not interfere with the electronics in the panel. Never allow field wiring to

come in close proximity with the controller boards since this will almost always cause problems.

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