Global label only appears once in the schematic

Diagnostic signature

Global label only appears once in the schematic

An Electrical Rules Check (ERC) diagnostic in KiCad that warns when a global label is placed only once across the entire schematic, indicating that it does not form any global connections.

What it means

In KiCad, global labels are designed to establish logical connections for a net across disparate sheets in a hierarchical or multi-sheet schematic. This ERC warning means that a placed global label has no identically named counterpart anywhere else in the project. Because the label exists in isolation, the tool interprets it as not actually fulfilling its primary purpose of establishing global net continuity. By default, this violation is often ignored in project settings to allow users the flexibility of using global labels simply to annotate nets for visibility, even if they do not route anywhere else.

Why it happens

The schematic contains a global label on a wire or pin, but no other global label with the exact same name exists within the design hierarchy. Common reasons include typographical errors in label names that prevent a matching connection, forgetting to place the matching label on a destination sheet, deleting one half of a previously paired global label, or intentionally using a global label instead of a local net label for purely local naming or aesthetic purposes.

Minimal reproduction

(kicad_sch (version 20231120) (generator eeschema)
  (sheet (number 1) (name "/") (tstamps "/")
    (title_block)
    (symbol (lib_id "Device:R") (at 50.8 50.8 0) (unit 1)
      (pin "1" (uuid 11111111-1111-1111-1111-111111111111))
      (pin "2" (uuid 22222222-2222-2222-2222-222222222222))
    )
    (wire (pts (xy 50.8 46.99) (xy 50.8 44.45)))
    (global_label "V_SENSE_OUT" (shape input) (at 50.8 44.45 90)
      (uuid 33333333-3333-3333-3333-333333333333)
    )
  )
)

How to fix it

Resolve the isolated global label by verifying its intended connection and either matching the label names, replacing it with a local label, or explicitly ignoring the violation.

```KiCad Schematic
(kicad_sch (version 20231120) (generator eeschema)
  (sheet (number 1) (name "/") (tstamps "/")
    (title_block)
    (symbol (lib_id "Device:R") (at 50.8 50.8 0) (unit 1)
      (pin "1" (uuid 11111111-1111-1111-1111-111111111111))
      (pin "2" (uuid 22222222-2222-2222-2222-222222222222))
    )
    (wire (pts (xy 50.8 46.99) (xy 50.8 44.45)))
    (label "V_SENSE_OUT" (at 50.8 44.45 90)
      (uuid 33333333-3333-3333-3333-333333333333)
    )
  )
)
```

Step 1

• Check the global label for typographical errors that may be preventing it from matching its intended counterpart on another sheet.

Step 2

• If the label is meant to connect to another sheet, locate the destination net and attach a matching global label with the exact same spelling and capitalization.

Step 3

• If the net does not need to cross into other sheets and is only being named for layout, simulation, or documentation purposes, delete the global label and replace it with a Local Label.

Step 4

• If you are intentionally using global labels as visual test points or for aesthetic purposes and expect them to be singular, suppress this warning by right-clicking the violation in the ERC dialog and selecting 'Exclude this violation', or by configuring the Schematic Setup ERC severities to ignore this specific rule.

Upstream references

Schematic Editor | master | English | Documentation - KiCad Docs

eeschema/erc/erc_item.cpp - KiCad Source Code - GitLab