Circuit C04 of the suite's worked example project. Current capacity alone would allow 70 mm²; cumulative voltage drop and the earth-fault loop push the cable to 95 mm².
| Load | Process pump P-101, 75 kW DOL motor, η 0.95, cos φ 0.86, starting current 7 × FLC at cos φ 0.3 |
| Supply | 400 V TN-S, from MCC-01 (Ik3 30 kA, Ik1 min 12 kA); upstream feeder C03 already drops 2.46 % |
| Cable | Cu/XLPE/SWA multicore, 150 m, on ladder (method E), 1 tier, 6 circuits touching |
| Site | Outdoor, shaded, air 50 °C |
| Protection | Motor starter: magnetic-only MCCB + overload relay, let-through I²t 1 × 10⁶ A²s |
| Limits | Circuit VD 3 %, total LV VD 5 %, starting VD 15 % (including 3 % bus dip) |
Open the Sizing Engine, click Load worked example project and select C04 to follow along.
With a motor starter the overload relay is set to Ib, so the cable must carry Iz ≥ 132.5 A.
IEC 60364-5-52 Table B.52.5, method E, three loaded conductors, Cu/XLPE:
| Size | Itab | Iz = 0.645 × Itab | ≥ 132.5 A? |
|---|---|---|---|
| 50 mm² | 192 A | 123.8 A | No |
| 70 mm² | 246 A | 158.7 A | Yes |
| 95 mm² | 298 A | 192.2 A | Yes |
70 mm² gives 2.90 % for the circuit but 5.35 % in total — over the 5 % limit. The upstream drop matters.
CPC to IEC 60364-5-54 Table 54.2: S/2 = 47.5 → 50 mm² (R2 = 0.4935 Ω/km at 90 °C). Ze from the bus: cmin·U0/Ik1 min = 0.95 × 230.9 / 12 000 = 0.0183 Ω. The MCCB magnetic pick-up Ia = 12 × 132.5 = 1 590 A.
70 mm² gives Zs = 0.172 Ω, which fails. The resistive part alone (0.1294 Ω) matches the hand calculation most designers do; the suite adds the loop reactance, which is safe side.
| Check | Requirement | Actual | Status |
|---|---|---|---|
| Current capacity | Iz ≥ 132.5 A | 192.2 A (95 mm²) | ✓ PASS |
| Total voltage drop | ≤ 5 % | 4.65 % | ✓ PASS |
| Motor starting drop | ≤ 15 % | 12.19 % | ✓ PASS |
| Short circuit | S ≥ 7.0 mm² | 95 mm² | ✓ PASS |
| Earth-fault loop | Zs ≤ 0.1380 Ω | 0.1321 Ω | ✓ PASS |
Key insight: On long motor circuits the cable is rarely sized by current. Always carry the upstream voltage drop into the check, and check the earth-fault loop against the magnetic pick-up of a motor-starter MCCB, which is high.
Every input in this example is editable in the live calculator — no signup needed.
Open Cable Engineering Suite (full workbench) calculator →A motor-starter MCCB is magnetic-only; its instantaneous pick-up is typically 10–14 × the overload setting. The suite uses 12 × by default — enter the actual setting in the Ia override field.
From circuit C03 (main switchboard to MCC-01), which the engine evaluates first because C04 starts at the bus C03 feeds.