A single-line diagram (SLD) is the most important drawing in any electrical project. Source on top, load at the bottom, protection and switching in between. Read it in this order, and you'll never miss a critical detail again.
Four ideas to carry into the next specification conversation you have.
Always start at the top (utility incomer or transformer secondary). Follow the path down through breakers, busbars, sub-distribution, to the final load.
Saudi projects use IEC: a circle with two crossing lines is a transformer, not a motor. Confusing the two reads is the #1 junior-engineer mistake.
Every breaker has rating + breaking capacity (Icu). The Icu at each level must exceed the short-circuit current at that point, that's selectivity.
Where SEC ownership ends, demarcation symbol appears. Where the metering CT/PT lives. Where the bus tie sits. These three define the whole architecture.
The 8 symbols that cover 90% of any Saudi commercial SLD.
| Symbol | What it represents | Reference |
|---|---|---|
| Circle + crossing lines | Transformer (two windings) | IEC 60617-06-09-01 |
| Two parallel lines + symbol | Circuit breaker (CB) | IEC 60617-07-08-03 |
| Triangle pointing down | Earth/ground connection | IEC 60617-02-15-01 |
| Cross in circle | Generator | IEC 60617-06-04-01 |
| Curved arrow | Variable transformer / VFD | IEC 60617-06-09-15 |
| Square + 'M' | Motor | IEC 60617-06-04-02 |
| Vertical zigzag | Resistor | IEC 60617-04-01-02 |
| Curve + arrows | Fuse / disconnector | IEC 60617-07-21 |
Five-step routine that scales from a small office to a Saudi mega-project.
Top of the drawing. Could be the SEC incomer, a generator, or a transformer secondary. Note the voltage, kVA rating, and impedance. This sets the available short-circuit current downstream.
The horizontal busbar(s) below the source. Single bus = simplest. Main-tie-main = N+1 redundancy. Ring bus = high-availability. The bus topology decides how a fault affects loads.
Each breaker has Icu (breaking capacity) and trip settings. Upstream breakers should clear after downstream, that's selectivity. Verify with the time-current curves.
Where the meter sits decides what gets billed. CT ratios decide measurement accuracy. Class 0.5S metering = revenue grade; Class 1.0 = monitoring only.
TN-S, TN-C-S, TT, IT, each Saudi project picks one. The earthing symbol at the transformer star point tells you which. Wrong earthing = wrong protection.
Our submittals include a fully annotated SLD with IEC 60617 symbols, protection coordination study, and arc-flash boundary markings, before the order is approved.
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