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Net labels and power flags

A net label gives a wire a name. Every wire end with the same label is connected, so a schematic stays readable without wires crossing the sheet.

What it is#

A net is everything that is electrically connected. A net label names it: draw a short wire from a pin, put a label LED_EN on its end, put another LED_EN label anywhere else (on another sheet too), and the two are connected as if a wire ran between them.

A power flag is a label with a symbol (a bar for supplies, a ground symbol for GND). It also tells the schematic check (ERC) that the net is a supply, so pins that need power on it are satisfied.

Example circuit: J1 and the LED driver share no wire; the two LED_EN labels join them. 5V and GND are power flags.
J1 and the LED driver share no wire; the two LED_EN labels join them. 5V and GND are power flags. Open the net_labels example from this page in PCB Canvas: “Insert into my schematic”.

Good habits#

  • Name nets after what they carry: SDA, LED_DATA, VBAT_SENSE, not NET12.
  • Use power flags for rails (3V3, 5V, VBUS, VBAT, GND) and plain labels for signals.
  • Labels connect exactly by name. SDA and sda or LED0 and LEDO are different nets; the ERC warns about look-alikes.

Pitfalls#

  • A label must sit on a wire end or a pin. A label floating next to a wire connects nothing (the ERC reports “label is not connected to any pin”).
  • An example inserted from this wiki keeps its label names, so its 3V3 and GND join your design’s nets. That is usually what you want; rename the signal labels if they clash.