What this error means
ERC groups everything on a sheet into connectivity clusters and flags any pin left in a cluster by itself — no wire to another pin, no label, nothing that could form a net. Two pin electrical types are exempt (Unconnected and Free), and a pin with a no-connect flag is routed to different checks entirely. A lone pin also passes if a matching global or local label elsewhere establishes its net name. Power symbols get no such rescue: anything not physically wired is flagged, since a forgotten power symbol looks exactly like one joined by name.
Two hierarchy cases report under this same code: a sheet pin with no wire on the parent sheet, and a hierarchical label placed in the root sheet, which has no parent to connect to.
Common causes
1. An unused pin with no no-connect flag
The everyday case. Spare gates, unused address pins, half of a dual op-amp: a pin you intend to leave open still fails ERC until you say so with a no-connect flag.
2. The wire does not actually land on the pin's connection point
The wire ends a little short, crosses the pin body instead of its end, or an endpoint is off grid. It looks connected at normal zoom, but the small circle on the pin end gives it away.
3. A dangling sheet pin or a hierarchical label in the root sheet
Sheet pins need a wire or label on the parent sheet like any symbol pin, and a hierarchical label in the root sheet has no parent to connect to.
4. A power symbol with nothing wired to it
A GND or +3V3 symbol floating in space names a net but connects to nothing.
How to fix it
Put a no-connect flag on every intentionally open pin
- Press Q (or Place → Add No-Connect Flag) and click the open pin end; an X replaces the circle.
- Repeat for each open pin — flags are per pin, not per symbol.
- Re-run ERC (Inspect → Electrical Rules Checker).
Use when: The pin is unused by design. This is the fix for most of these errors.
Re-land the wire on the pin end
- Zoom in on the flagged pin: an open pin end shows a small circle.
- Drag the wire endpoint onto the circle, or redraw the segment with W starting from the pin.
- If things have drifted off the 50 mil grid, select the area, right-click → Align Elements to Grid, then re-run ERC.
Use when: You believe the pin is connected; the report's coordinates point at the exact spot where the wire misses.
Wire or remove the dangling hierarchy item
- For a sheet pin: connect a wire or label to it on the parent sheet, or delete it if obsolete.
- For a hierarchical label in the root sheet: delete it, or cut it and place it inside the intended subsheet.
- Re-run ERC.
Use when: The report points at a sheet symbol's edge or at a hierarchical label on your top-level sheet.
When it’s safe to exclude
Rarely: the no-connect flag is the exclusion mechanism, applied pin by pin where a reviewer can see it. Excluding wholesale (right-click the marker → Exclude, or downgrading it in Schematic Setup → Electrical Rules → Violation Severity) hides the near-miss wires and forgotten power symbols along with the harmless open pins. The one defensible use is a schematic you are deliberately leaving half-wired: downgrade to warning while drafting, put it back before you sign off.
Gotchas
- Stacked pins do not rescue each other: a stack with nothing else on it counts as one dangling cluster and flags once.
- An unconnected input pin reports twice: once here and once as
pin_not_driven. Fixing the connection, or flagging it, clears both. - A no-connect flag on a pin that is connected trips
no_connect_connectedinstead. Flags are for open pins only. - A symbol with forty unused pins needs forty flags — tedious, and still the intended workflow.
Minimal reproduction
Drop a resistor, wire one end, leave the other bare, and run ERC (Inspect → Electrical Rules Checker). The bare pin reports:
[pin_not_connected]: Pin not connected
; error
The checked-in file data/erc/samples/pin_not_connected.kicad_sch
reproduces this with a single embedded one-pin Passive symbol and no
wires, so this is the only error. The one lib_symbol_issues warning
about the missing repro library is an artifact of the self-contained
file. Adding a no-connect flag at the pin end drops the error count to
zero — fix #1 in miniature.
Related errors
- Input pin not driven by any Output pins (reference page coming soon)
- A pin with a "no connection" flag is connected (reference page coming soon)
- Unconnected "no connection" flag (reference page coming soon)
- Symbol pin or wire end off connection grid (reference page coming soon)
FAQ
ERC says a pin is not connected while it is obviously connected. Why?
The wire is almost certainly ending next to the pin instead of on it. Zoom in on the reported coordinates: an unconnected pin end draws a small circle, and if you can see it the wire missed. Drag the endpoint until it snaps onto the pin end, and keep wiring on the default 50 mil grid.
How do I tell ERC that a pin is intentionally unconnected?
Place a no-connect flag: press Q (or Place → Add No-Connect Flag) and click the pin end. The X marker tells ERC the pin is open on purpose. The Unconnected pin electrical type also works, but that change belongs in the symbol library, not one schematic.
Why does one unconnected pin produce two ERC errors?
An unconnected input pin violates two independent checks: "Pin not connected" because it joins no net, and "Input pin not driven by any Output pins" because there is no driver. Connect it or flag it and both disappear together.