Numbering System & Symbols Library - General

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Wire number

• Ensures every wire can be uniquely identified in the schematic and in the physical panel.

• Makes it possible to trace a wire from one page to another and in the field during troubleshooting.

• Prevents confusion when many wires run side by side inside a panel or cable tray.

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Device Number

• Provides a unique identifier for each component (like motors, relays, pushbuttons).

• Allows engineers, electricians, and programmers to refer to the same device without ambiguity.

• Essential for connecting schematics, PLC logic, and the panel layout.

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Panel Number

• Shows which physical panel a device or terminal belongs to in multi-panel systems.

• Keeps complex systems organized (for example: Panel 1 in the MCC vs. Panel 2 in the field).

• Helps maintenance staff locate the correct enclosure in the plant.

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I/O Address

• Maps wiring in the schematic to the PLC program logic.

• Ensures that physical signals (like a sensor wired to input slot 3, terminal 5) match software addresses (like I:3/5).

• Provides the crucial link between hardware design and software control.

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Wire Continued Elsewhere

• Indicates that a wire does not end on the current drawing but continues on another page.

• Keeps drawings uncluttered by avoiding long wire paths across the sheet.

• Lets someone flipping through the schematics follow the circuit quickly via cross-references.

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Terminal Block, Panel

• Represents the interface point where field wiring meets the control panel wiring.

• Provides a structured way to connect/disconnect wires without disturbing the internal panel wiring.

• Helps electricians know exactly where to land external cables inside the panel.

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Bill of material, item number

• Links schematic components to actual physical parts to be purchased/assembled.

• Ensures accuracy in procurement (correct model, rating, vendor).

• Creates a one-to-one map between the drawing and what’s physically in the panel.

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Earth ground

• Provides a direct safety path to the physical earth.

• Protects equipment and people from electrical faults, lightning, or static buildup.

• Required for compliance with electrical safety standards.

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chassis ground

• Ties circuits to the conductive body/frame of the equipment.

• Reduces electrical noise and interference in sensitive control systems.

• Provides a safety return path for fault currents inside the enclosure.

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resistor (res)

• Controls current flow or voltage levels in a circuit.

• Used in controls for signal conditioning (e.g., scaling analog signals or protecting inputs).

• Can act as pull-up/pull-down resistors in PLC input circuits.

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revision

• Tracks changes made to the drawing set over time.

• Provides a history of modifications (who changed what, when, and why).

• Critical for ensuring that electricians and engineers are always working off the correct drawing version.

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device terminal

• Identifies the exact connection points on a device (like a relay coil or PLC input card).

• Helps electricians know which screw or lug to attach a wire to.

• Ensures wiring is done correctly so the device functions as intended.

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plug

• Represents a detachable connector that allows two parts of a system to be separated easily.

• Facilitates modular design, easy maintenance, and quick replacements.

• Ensures reliable connections in environments where vibration or movement is common.

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