Distribution Box Line Head Number

The Distribution Box Line Head Number identifies the main incoming line or feeder in a distribution box, serving as a reference for circuit management and labeling.

Definition and Purpose

A line head number in a distribution box refers to the unique identifier assigned to the incoming line or main feeder entering the distribution panel. This number is used to: Track and reference the source of power entering the distribution boxIdentify which circuit breaker or isolator corresponds to a particular incoming lineFacilitate maintenance, troubleshooting, and load managementEnsure proper documentation in single-line diagrams and load schedules. Components Associated with Line Head NumberIn a typical distribution box, the line head number is linked to the following components: Incoming Line Part: Shows the source of power, which may be a single line or multiple lines (normal and backup supply), along with the circuit breaker model and rated breaking current.

Circuit Breakers or Isolators: Each incoming line is protected by a breaker or isolator, and the line head number helps identify which breaker corresponds to which source. Busbars and Feeders: The line head number is associated with the busbar and feeder droppers that distribute power to outgoing circuits. Dual Power Switch (if applicable): In systems with dual incoming lines, the line head number helps manage automatic switching between normal and backup power.

Numbering and Labeling Standards

Each incoming line is assigned a unique reference number (e.g., RYB-01, RYB-02) that appears in the single-line diagram (SLD) and on the distribution box itself. The numbering system ensures that phase sequence (R, Y, B) and neutral connections are clearly documented. Outgoing circuits are also labeled in relation to the line head number to maintain clarity in load distribution and protection settings.

Practical Example

For instance, in a substation LT panel: Main Incoming Ckt.

CK

T REF.: RYB-03 indicates the third incoming line from the transformer or generator. The line head number is referenced in the load table and single-line diagram, showing which busbar and outgoing circuits it feeds. Protective devices, such as circuit breakers or isolators, are marked with the same reference to ensure proper identification during operation or maintenance.

Key Takeaways

The line head number is essential for safe and organized electrical distribution. It links the incoming power source to the distribution box, busbars, and outgoing circuits. Proper labeling according to standards ensures efficient maintenance, fault isolation, and load management.

Always refer to the single-line diagram and load schedule for accurate identification of line head numbers in any distribution system.