What this error means
For every pin of a placed multi-unit symbol, ERC records which net the
pin is on, keyed by reference designator plus pin number (U1:8). The
moment that key turns up on a second, different net, the check fires,
with a marker pointing at both drawn copies of the pin.
One pin number in two places means the symbol shares the pin between units: it is either marked common to all units in the Symbol Editor, or the same supply pin is drawn in more than one unit, old op-amp style. Every drawn copy is a connection point for the same physical pin, so all copies have to land on one net.
A copy you left unconnected still counts: it gets an auto-generated net of its own, so the report reads "Pin 3 is connected to both /VCC and unconnected-(U1B-COM-Pad3)". The title above never appears at runtime — only in the Violation Severity list.
Common causes
1. A shared supply pin is wired in one unit and not the others
The classic op-amp case: the symbol draws V+ and V− in more than one unit (or marks them common to all units), you wire them at unit A, and the copies at units B, C, D are left dangling or picked up a different label. Each untouched copy sits on its own auto-named net, which is a different net, so every one of them raises this error.
2. Two physical parts share one reference designator
The check identifies a symbol by its reference, so when two
different packages are both called U1, their pins with the same
number look like one shared pin on two nets. duplicate_reference
will be in the same report; fix that one first.
3. A hand-made symbol reuses a pin number across units
If two different physical pins in two units were both entered as pin 8, ERC insists they join the same net even though they should not. The schematic is fine; the symbol is wrong.
How to fix it
Wire every drawn copy of the shared pin to the same net
- Click one of the two positions in the marker and press the highlight-net key (backtick) to see which net each copy landed on.
- Decide which net is right, then rewire or relabel the other unit's copy to match — including copies that are not wired at all.
- Re-run ERC (Inspect → Electrical Rules Checker).
Use when: The symbol shows the same supply or common pin in more than one unit. This is the 80% case.
Fix duplicate reference designators first
- If the two marker positions are on two different packages, the parts are sharing a reference, not a pin.
- Run Tools → Annotate Schematic… to give every symbol a unique reference.
- Re-run ERC; this error and its accompanying duplicate_reference usually clear together.
Use when: The marker points at what you know to be two separate components.
Give each physical pin its own number in the symbol
- Open the symbol in the Symbol Editor (right-click → Edit Symbol).
- Check each unit for the flagged number; if two genuinely different pins carry it, renumber one to match the datasheet.
- Save, update the symbol in the schematic, and re-run ERC.
Use when: Your own symbol reuses a pin number across units. Only edit symbols you maintain.
When it’s safe to exclude
Almost never. The check reports one physical pin being told to join two nets — a contradiction, not a style complaint. Only one of the two connections you drew can exist on the board, and excluding the marker (right-click → Exclude) just hides which one loses.
Downgrading the whole check in Schematic Setup → Electrical Rules → Violation Severity is worse: it also silences the op-amp-supply and duplicate-reference cases, which produce boards with floating power pins. If the error is firing on a correct schematic, the symbol is lying about its pin numbers; fix the symbol instead.
Gotchas
- "But I only connected it once" is exactly how the error happens: the copy you never touched is on its own net named unconnected-(U1B-COM-Pad3), and that counts as a different net.
- The marker lists two positions for what is, electrically, one pin. ERC is not seeing double; your symbol draws it twice.
Minimal reproduction
Make a two-unit symbol with one pin marked common to all units, place both units, and wire each unit's copy of that pin to a differently named net. Run ERC:
[different_unit_net]: Pin 3 is connected to both /NET_A and /NET_B
; error
@(119.38 mm, 101.60 mm): Symbol U1 Pin 3 [COM, Passive, Line]
@(119.38 mm, 127.00 mm): Symbol U1 Pin 3 [COM, Passive, Line]
The checked-in data/erc/samples/different_unit_net.kicad_sch does
this with an embedded two-unit symbol whose unit-0 pin 3 appears in
both placed units, one wired to NET_A and one to NET_B; the two
lib_symbol_issues warnings are artifacts of the embedded repro
library. Renaming NET_B to NET_A drops the error count to zero under
9.0.3 — fix #1 in miniature. Deleting the NET_B wire instead yields
"connected to both /NET_A and unconnected-(U1B-COM-Pad3)" — the
dangling-copy case.
Related errors
- Different footprint assigned in another unit of the symbol (reference page coming soon)
- Units of same symbol have different values (reference page coming soon)
- Duplicate reference designators (reference page coming soon)
FAQ
I connected power to one unit of my op-amp — why does ERC flag the power pins on the other units?
The symbol draws the same physical supply pins in more than one unit, and each drawn copy is a connection point for that pin. A copy left unconnected sits on its own auto-generated net, which KiCad treats as a different net from your power rail. Wire the supply copies in every unit to the same rail, or use a symbol variant that collects the power pins in one dedicated unit.
Can I connect each unit of a symbol to a different supply rail?
Not through a shared pin: the units are one physical package, and a shared pin is one piece of metal. If a part genuinely has separate supply pins per section, those pins have different numbers on the datasheet; a symbol that numbers them that way can wire them to different rails without triggering this check.
What was ErrType(12): 'Different net assigned to a shared pin in another unit of the same component'?
The same check under its pre-KiCad-6 wording — old forum threads use "of the same component" and a numeric ErrType. The mechanics have not changed, and old-thread advice about wiring every drawn copy of the pin to one net still applies.