Why a connection is refused

When a wire cannot be created, UnifCAD does not fail silently: a short badge appears with the reason. There are three.

"A cable already exists between those two points"

Those two terminals are already joined. A second identical wire would add nothing to the circuit and would sit invisibly on top of the first one.

If what you actually want is a second path — for example feeding a third device from the same point — draw the wire onto the existing run instead of onto the terminal. That creates a junction and a branch. See branching.

"The pin reached its maximum number of connections"

A terminal is a physical screw, and it takes a limited number of conductors. When it is full, the answer is not to force another wire in — it is to splice: run the new wire onto the conductor that already leaves that terminal.

That is what an electrician does with a terminal block, and it is what the junction represents.

"Incompatible connection: AC and DC cannot be joined"

One end belongs to an AC system and the other to a DC one. This is refused on purpose: joining them is not a drawing mistake you can shrug off, it is a short between two supplies.

Check which supply feeds each side of the sheet. A 24 V DC control circuit fed from a power supply and a 230/400 V AC power circuit are two separate systems, and they meet only through a device that is built to bridge them — a relay coil, a contactor, a PLC input.

Terminal numbers: the label is not the identity

Every numbered contact block carries a number — 13-14, 21-22, 23-24. In UnifCAD that number follows EN 50005:

• the tens digit is the position of the block in the device,
• the units digit is its function: 1-2 for a normally closed contact, 3-4 for a normally open one.

So the second auxiliary block of -KM1 is 23-24, not a second 13-14.

Changing a number

Open the component and go to the Terminal numbers section.

• Type the numbers you want. A blank field is a valid answer: it means "the catalog number".
• Next free block fills in the next unused block — 23-24, then 33-34 — in one click.
• What you write stays written. Renaming the device, moving it to another device, or reordering the sheet will not renumber it behind your back.

Repeated numbers are allowed: two blocks bought separately both arrive stamped 13-14, and that is a legitimate drawing.

Terminals whose number is their meaning are not editable, because changing them would be wrong rather than merely unusual: the 95-96 / 97-98 of a thermal relay, and the timed contacts of a timing relay.