A contactor's contact is on the third page, its coil on the first. The only thing binding those two points together is the label written at both. That small binding is what makes a panel readable: see the label, find the other end. The problem is that this binding is written by hand.
Why cross-reference errors are dangerous
A cross-reference shows that a circuit continues on another page. Maintained by hand, three types of error naturally occur:
- Stale reference: the device is renamed, one end of the reference keeps the old name. The reader follows the wrong device.
- Missing reference: a new circuit is drawn, the opposite-side reference is forgotten. The circuit ends in mid-air.
- Wrong page: the reference points to the right device but the page number changed in a revision.
The common thread: a reference is written in two independent places. When one changes, the other does not follow.
The fix: references derived from the tag
In EupCAD, cross-references are not written by hand; they are derived from the IEC 81346 tag. The device's address comes from a single source — the device's own definition — and that address appears automatically at both ends of the circuit. The result:
- When you change the tag, both ends update in the same step; a stale reference cannot exist.
- When a new circuit is drawn, the opposite reference appears automatically; it cannot be forgotten.
- When the page layout changes, the references are recalculated.
The reference is a product of the data, not of the drawing; because the data is single, the reference can never drift from the drawing.
Practical scenario: a multi-page pump circuit
In the demo project (ZONE1_PUMPS), a pump's coil and its contact are on different pages. The label appears at the same address on both pages; when you move between the pages, the reference still points to the same device. Change the device's tag and you will observe both sides of the reference changing together.
In the old flow this update would have required two separate manual edits. In the single-source flow there is one edit: the device's definition.
Next step
In the demo project, move between the pages: find a circuit's label at one end, match it to the reference on the opposite page. Change the device's tag and watch both ends update together.