1. Basic Principles of Circuit Numbering

Any control cables connecting different equipment through terminals should follow the circuit numbering principles. Additionally, some devices installed on the top of the panel and connected to devices inside the panel through terminal blocks should also be numbered according to the circuit numbering principles, treating the top devices as external equipment.

All electrical components and wires inside and outside the control cabinet must have numbers that match those on the electrical schematic diagram. This consistency is crucial for installation and maintenance of electrical circuits. The principles to follow are simplicity, ease of memorization, clear differentiation, aesthetic appearance, and clarity at a glance.

To ensure clarity, different numbering methods are used for DC and AC circuits. Various types of circuits within AC and DC circuits are assigned different numerical symbols. This way, when we see a number in the secondary circuit wiring diagram, we can understand the nature of the circuit, making maintenance and repair easier.

2. Basic Methods for Secondary Circuit Numbering

Using Three or Fewer Digits: Numbers can be composed of up to three digits. If it is necessary to indicate the phase or certain main characteristics of the circuit, alphanumeric symbols can be added before or after the numbers.

Marking by "Equipotential" Principle: In an electrical circuit, all wires connected to a single point (including segments that can be bent to make contact) must be given the same circuit number.

Different Segments of Electrical Components: The segments between the contacts, coils, resistors, capacitors, etc., of electrical equipment are generally given different numbers. For circuits that are directly connected inside the panel without passing through terminals, numbering may not be necessary.

3. Detailed Rules for DC Circuit Numbering

Different Uses, Different Ranges: Different ranges of numbers are used for different purposes. For example, control and protection circuits use numbers from 001 to 099 and 101 to 599, while excitation circuits use 601 to 699.

Grouping by Fuses: Numbers used for control and protection circuits are grouped according to the fuses' circuits, with each hundred numbers forming a group. For example, 101 to 199, 201 to 299, 301 to 399, etc. Within each group, positive polarity circuits (odd numbers) are numbered from small to large, followed by negative polarity circuits (even numbers) from large to small, such as 100, 101, 103, 133, 142, 140, etc.

Signal Circuits Grouping: Numbers for signal circuits are grouped by function such as fault, position, warning, and command signals and are arranged numerically.

Control Circuit Numbers for Switchgear: The numbering group for control circuits of switchgear should be selected according to the sequence number of the switchgear. For example, if there are three control switches 1KK, 2KK, and 3KK, the control circuit numbers corresponding to 1KK are 101 to 199, for 2KK are 201 to 299, and for 3KK are 301 to 399.

Odd and Even Numbering for Polarities: Segments of positive circuits are marked with odd numbers, while segments of negative circuits are marked with even numbers. The polarity changes after each main voltage drop component (e.g., coils, windings, resistors), changing the odd/even sequence accordingly. For segments that cannot indicate polarity or whose polarity changes during operation, either odd or even numbers can be used.

Specific Number Groups for Major Circuits: Specific numbering groups are usually assigned for certain major circuits. For instance, the positive power supply is numbered 101, 201, and the negative power supply is numbered 102, 202. Green lamp circuits in the closing circuit are numbered 105, 205, 305, 405. Red lamp circuits in the tripping circuit are numbered 35, 135, 235, etc.

4. Detailed Rules for AC Circuit Numbering

Phase Order Numbering: AC circuits are numbered according to phase order. In addition to using three-digit numbers, alphanumeric symbols are added to distinguish them, such as A411, B411, C411.

Different Uses, Different Groups: Different number groups are used for different purposes. For current circuits, numbers are generally grouped in tens. For example, A401 to A409, B401 to B409, C401 to C409, etc., up to A591 to A599, B591 to B599. If necessary, groups of twenty can be used for a set of current transformers. The parallel circuits of multiple sets of current transformers should start with the smallest group of numbers. For different-phase current transformer parallel circuits, any one phase's number group can be used. Voltage circuit numbers are also grouped in tens, such as A601 to A609, B601 to B609, C601 to C609, A791 to A799, etc., for a single transformer circuit.

Current and Voltage Transformer Circuits: Circuits of current and voltage transformers must be numbered sequentially within the assigned number ranges, starting from the transformer terminals. For example, "TA" circuit numbers are 411 to 419, and "2TV" circuit numbers are 621 to 629.

Special AC Circuits: Certain specific AC circuits (e.g., common circuits for bus differential protection, common circuits for insulation monitoring voltmeters) are given specific number groups.