I’m putting together the documentation for a small panel we build over and over: a DIN rail with a 24 V supply, an RS485 gateway that reports to Hermetry, a couple of 4-20 mA isolators, fuses and two terminal strips, one for field power and one for signals. The customer wants a proper wiring diagram, not my hand sketches.
I’m self-taught on drawings. I’ve seen terminals drawn as little circles, as squares, as numbers in a row, some drawings have “X1:3” labels and some have “TB1-3”. What’s the normal way? Our customers are mostly in the UK and Ireland if it matters which standard. Also, do I draw every terminal in the schematic, or is there a separate list?
US work is mostly the ANSI/NFPA-79 habits (TB1-3 style), Europe is IEC. Since your customers are UK/IE, go IEC.
We did this in our control systems module last term and I’ve since drawn a few panels for a summer job, so here’s the IEC way as we were taught it.
Designation: IEC 81346 letter codes, terminal strips are X. First strip -X1, second -X2. A single terminal is the strip plus its number with a colon: -X1:3. Equipment gets its own code too: power supply -T1, fuses -F1, the gateway maybe -A1.
Symbol: IEC 60617 draws a terminal as a small circle (or a small square, many CAD libraries use that for terminal blocks) with the number next to it, on the wire where it passes through the strip. You don’t draw the whole strip as one box in the circuit diagram, each terminal appears where its wire is.
Then a separate terminal diagram (terminal plan) per strip: a table, one row per terminal, with internal destination on one side (e.g. -A1:A+) and external cable/core on the other (W12 core 1). Electricians wiring on site work almost only from that list.
A few habits that made my drawings get fewer questions:
- Keep field power and signals on separate strips like you do, and say so in the strip’s title (X1 24 V field, X2 RS485 + 4-20 mA).
- Draw jumpers between terminals explicitly.
- For the RS485 terminals, mark A/B and the shield terminal clearly and note where the 120 Ω termination sits.
QElectroTech is free and has IEC terminal symbols plus terminal plan generation, if you’re not on a paid CAD.
Thanks Aoife, that’s the structure I was missing, especially the terminal plan as a separate sheet. Redrew our standard panel in QElectroTech (thanks Brian) with -X1/-X2 and a terminal plan per strip. First customer review came back with one question instead of ten.
Add a revision block too, the second version always comes.
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