Nets, labels and power

A net label is scoped to its own schematic unless you promote it.

• A local name means something only within the sheet it is on. Two sheets can each carry a local MOSI and they are two different nets, which is exactly what you want when the name is a sheet-internal signal.
• A global name merges across every sheet under the same board.
• Power symbols are always global. That is the definition of a power symbol.

Toggle the scope with Tab while the label ghost is on the cursor, or right-click a placed label and choose "Make net global to the board" / "Make net local to this sheet".

Scoping only works if you can see it, so a global label renders in a different colour with a chevron outline. It is not something you have to remember about a sheet you drew last month.

Scoping introduces exactly one way to get burned: you label MOSI on sheet 3, it is global on sheet 1, and you believe you connected them. The rules check watches for precisely that and reports it (local_shadows_global). That warning is the price of having scoping at all, and it is why the rule exists.

• A global name beats a local one on the same net.
• A net carrying several names uses the first alphabetically and reports the rest, rather than silently picking one and letting you find out later.
• Unlabelled nets get N$1, N$2 and so on, ordered by their lowest connected pin — so editing one corner of a sheet doesn't renumber everything else.
• Two genuinely different nets that legitimately carry the same local name on different sheets get a display suffix (SIG, SIG(2)). They are not merged. That is what local scope means.

A power symbol whose name encodes a voltage — 5V, +5V, -12V, +3.3V, 3V3, 1V8 — doesn't just label the net. It powers it. 5V ─ 10k ─ 10k ─ GND is a working divider with no source part placed at all, which is how you want to sketch a bias network.

That only happens when nothing else drives the net. Put a battery, a regulator output or a voltage source on +5V and the rail steps aside — two ideal supplies on one node is a short, and the simulator would refuse it.

A rail is always plain DC at the voltage in its name. A sine or a variable supply takes a real source, because a rail labelled 5V that was secretly a 1 kHz sine would be a lie printed on the sheet.

Two things are reported instead of guessed:

• A rail named VCC, VDD or VBAT has no voltage in its name, so nothing drives it. Assuming 5 V would be silently wrong on every 3.3 V design.
• If nothing drives the circuit at all, that is said out loud — every voltage reading exactly zero looks identical to a broken solver otherwise.

A bus label is a range: D[0..7], ADDR[3..0]. It expands to its members and every member name lands on the labelled net. Reversed ranges expand in reverse.

A pin marked hidden in the library connects by name to the global power net of the same name — the classic convenience for parts that don't draw their supply pins. It is reported as an informational note on every derivation, so a connection you can't see on the sheet is never one you don't know about.

Turn on net highlight in the bottom bar and hovering lights up the whole net rather than the one segment under the cursor. A net is the thing that matters, so the net is what lights up.