The terminal strip is the densest place in the panel. On a strip with four hundred terminals, every number carries meaning: 13 brings L1 in, goes out to 14, 21 supplies the 24V, 22 takes the motor phase. The person tying the wires does not know what 13 is for; he knows it is 13, and he reads where it goes from the schedule.
That is why the terminal schedule is a document that lives far longer than the drawing. The drawing finishes its job when the panel is built. The schedule is read for the life of the panel: while wiring, while hunting a fault, and again when a new crew comes to touch it years later. Two different people read the same schedule: the first one ties the wires, the second one tries to work out why something is there.
Two conductors on one number
Let the number 13 appear twice on a strip. The first goes to a contactor coil, the second to a heater circuit. If the wiring order is right, both conductors land in their places. The panel works. The tests pass. At first glance the error burns nothing.
Then a change comes: that coil circuit is revised, and number 13 shifts to a different job. The person tying the wire sees 13 in the schedule and cannot tell which 13 it is. A conductor goes to the wrong terminal and feeds the wrong circuit. The motor runs the wrong way, the sensor never comes, the heater never cuts. Which one happens depends on the circuit.
This error type is the quietest of all panel errors. A short circuit blows something; an open circuit shows up immediately. A number conflict works silently and is usually found by accident. When it is found, the bill is big, because every wrongly tied terminal has to be found and corrected one by one.
How a terminal duplication happens
In a schedule maintained by hand this error is almost unavoidable. The strip grows, the numbers continue; the block in the spreadsheet is the old one, the block in the drawing is the new one. Nobody bothers to lay the two sources on top of each other, because each one looks consistent on its own. The moment a schedule is written down, it becomes a separate living thing from the drawing; when the drawing changes, the schedule does not.
In EupCAD the terminal schedule is not written separately; it is produced from the terminals in the drawing. Strip number, terminal number, type, deck count, inner and outer labels, cable and page come from the same source as the drawing. A repeated number, not being written in two places, cannot be half-fixed with "I corrected it in one of them".
The columns, and the one that saves the day
Every column in the terminal schedule has a different reader. The type column says what the terminal is in the strip: standard, neutral or earth. The deck count says how many channels the terminal has. The cable column shows which cable enters that terminal.
The column that saves the day is the fourth one: the outer label, where the terminal goes. A terminal number is a meaningless string of characters on its own; it gets its meaning from where it is connected. 13 is nothing by itself. 13 becomes a circuit when it says "-K1 coil A1". The fault crew looking for a fault does not search the drawings; they search this mapping. The page column does the same job: jumping to a page without having to ask which page the terminal is on.
The inner and the outer label
A terminal has two sides. The side facing inside the panel knows the circuit: which contact, which coil, which PLC address. The side facing out knows the cables: the cable number entering that terminal and the device on the far end. The person tying the wires reads the inner label, the person pulling cables reads the outer one.
That is why the schedule keeps the two labels in separate columns. Writing them together as one would squeeze two jobs into a single reading. In EupCAD the terminal data keeps the two labels apart, and they appear separately in the schedule.
Jumpers: the connection you do not see
A terminal can be connected to its neighbour with a bridge without any cable going to it at all. That is a jumper; it is wiring without a cable. If a jumper is not visible in the terminal schedule, the connection is not in the schedule. The person tying the wires does not make the jumper, the circuit stays open. The "why is this circuit not working?" question in the test comes from the jumper missing from the schedule.
In EupCAD's terminal schedule the jumper is a column of its own; a terminal with a bridge set is marked in the schedule. A jumper is not numbered like a cable, but it is visible like one.
Terminal type: three different jobs
The type of a terminal says what it does in the strip: standard, neutral or earth. Earth terminals and standard terminals have different colours and shapes in the strip; mixing them is an unacceptable error in safety terms. If a neutral terminal is tied next to an earth terminal, the neutral current gets a chance to return over the earth path.
The type column makes the terminal's job visible in the schedule. The layout in the strip is checked against the type column; that the earth terminals are gathered in a block of their own, that the neutrals sit in a block of their own, is read row by row from the schedule.
The page column: the schedule is a map of the drawing
The page column in the terminal schedule says which page of the drawing the terminal is on. In a fault, going down from a terminal number to the drawing is one step with the page column. Without it, finding which page the same terminal is on means walking through the pages one by one.
In EupCAD, touching a row in the terminal schedule jumps to that terminal in the drawing. The schedule is a map of the drawing; every point in the map goes to the real place in the city.
The rule check looks at the numbers
EupCAD's rule check groups the terminals by strip and number. If the same number comes up twice on the same strip, the report shows "Warning: Terminal duplication: X1:13 (2 times)". Which strip, which number, how many times.
The value of this check is that it catches the error at the cheapest moment. Before the wiring starts, in the office, one line in the report. Finding the same error after the wiring has started means walking the strip terminal by terminal, and that is mostly done on site.
The document read at fault time
The panel is built, the fitting crew leaves. When the same panel fails years later, what is left in the fault crew's hands is, most of the time, the terminal schedule. Collecting the terminals from the drawings, page by page, at fault time is not a job to do at that moment. Reading it from the schedule takes fifteen minutes; losing fifteen minutes between pages is something else.
If the terminal schedule is produced together with the drawing, this problem goes away: the schedule is a view of the drawing. It is not a separate document, and it does not carry a separate risk of going stale.