Detailed Description
One Conductor, Many Advantages — The Modular Approach
The conventional way to connect a servo motor is with a 4-core shielded cable — three phases plus ground in one sheath. It works. But it forces the entire cable bundle to follow a single path in the carrier, at a single bend radius, and to be replaced as a single unit when any part fails.
Individual single core cables offer a fundamentally different approach:
- Flatter carrier layout: Instead of a 22 mm round bundle, three 8 mm single cores arranged side by side in a 8 × 28 mm flat pattern — reducing the carrier height requirement by 64%
- Independent bend radius: Each core follows its own optimal path. The inner bend radius core can run closer to the carrier's neutral axis
- Phase-level replacement: A manufacturing defect, installation error, or localized damage affects one phase — not the entire motor cable. Replace one single core, not four conductors
- Modular inventory: Stock single cores in standard cross-sections and colors. Assemble motor cable sets on demand — no need to stock dozens of multi-core configurations
Cross-Section and Current Selection Guide
| Cross-Section | OD (PVC) | Continuous Current* | Typical Motor (400 V) | Carrier Space (3 phases flat) |
|---|---|---|---|---|
| 0.5 mm² | 2.5 mm | 8 A | Signal/control only | 7.5 × 2.5 mm |
| 0.75 mm² | 2.8 mm | 11 A | Up to 2.2 kW | 8.4 × 2.8 mm |
| 1.0 mm² | 3.1 mm | 14 A | Up to 3.0 kW | 9.3 × 3.1 mm |
| 1.5 mm² | 3.5 mm | 18 A | Up to 5.5 kW | 10.5 × 3.5 mm |
| 2.5 mm² | 4.2 mm | 24 A | Up to 7.5 kW | 12.6 × 4.2 mm |
| 4 mm² | 5.1 mm | 32 A | Up to 11 kW | 15.3 × 5.1 mm |
| 6 mm² | 5.8 mm | 41 A | Up to 15 kW | 17.4 × 5.8 mm |
| 10 mm² | 7.2 mm | 57 A | Up to 22 kW | 21.6 × 7.2 mm |
| 16 mm² | 8.5 mm | 76 A | Up to 30 kW | 25.5 × 8.5 mm |
| 25 mm² | 10.8 mm | 101 A | Up to 45 kW | 32.4 × 10.8 mm |
| 35 mm² | 12.5 mm | 125 A | Up to 55 kW | 37.5 × 12.5 mm |
*Continuous current at 30°C, single cable in free air per IEC 60364-5-52. Derate for elevated temperature or multiple cables in contact.
Color Coding — Standards and Best Practice
Consistent color coding prevents wiring errors and simplifies maintenance:
| Phase | EU (IEC 60445) | Common Industrial Practice | Function |
|---|---|---|---|
| L1 / U | Black | Black | Phase 1 |
| L2 / V | Black (numbered) | Red or blue | Phase 2 |
| L3 / W | Black (numbered) | Blue or red | Phase 3 |
| PE / Ground | Green-Yellow | Green-Yellow (mandatory) | Protective Earth |
| DC+ | Not standardized | Red | DC bus positive |
| DC- | Not standardized | Black or blue | DC bus negative |
Installation — Routing Single Cores Together
- Bundle with spiral wrap: After routing three phases through the carrier, bundle them with PUR-compatible spiral wrap at 200–300 mm intervals. This prevents individual cores from migrating to different carrier lanes while still allowing independent movement during flexing
- Equal-length phases: Cut all three phases to the exact same length within ±10 mm. Unequal lengths create phase impedance imbalance, increasing common-mode current in the ground conductor
- Flat arrangement: Route phases in a single horizontal layer — black, red, blue — never stacked vertically. Stacked cores experience different bend radii at carrier curves, creating unequal phase impedances
- Carrier dividers: If the carrier has vertical dividers, use them to separate phases — one phase per lane. If no dividers, maintain ≥1× cable diameter spacing between phases
- Strain relief: All three phases (plus ground) should be clamped in a single multi-hole strain relief plate at both ends. This ensures equal strain distribution — clamping individual phases separately creates unequal tension
Single Core vs Multi-Core — The Trade-offs
| Consideration | Multi-Core Motor Cable | Single Cores (3 + PE) |
|---|---|---|
| Installation time | One cable pull | Four cable pulls |
| Carrier height | Single cable, ~22 mm OD (4 × 16 mm²) | Three cables, ~8.5 mm each — flat arrangement possible |
| Bend radius | 7.5 × 22 = 165 mm | 7.5 × 8.5 = 64 mm each |
| Capacitance (phase-ground) | Higher (cores bundled) | Lower (cores separated) |
| VFD reflected wave | Higher risk (higher capacitance) | Lower risk |
| Replacement cost | Entire cable | Single phase |
| Connector compatibility | Standard 4-pin motor connector | Individual ring terminals or busbars |
| Inventory | Stock multiple multi-core types | Stock single cores — assemble on demand |
When NOT to Use Single Cores
- Space-constrained connectors: If the motor connection is a single 4-pin circular connector, single cores cannot be terminated directly — an intermediate junction box is needed
- High-flex, high-density: If the carrier already contains 20+ cables, adding 4 single cores (vs 1 multi-core) increases carrier fill and management complexity
- Long, unsupported spans: If the cables exit the carrier and run unsupported before entering the motor junction box, single cores require individual support — a multi-core cable is self-supporting
Why Choose Yichi Cable Single Core?
- Full color range from stock: Black, red, blue, green-yellow in all standard cross-sections — no minimum order
- Class 6 option for tight carriers: Need 5×D bend radius? Class 6 ultra-fine stranding available for cross-sections up to 35 mm²
- Cut-to-length service: Order exact lengths — no waste, no splicing, no "we ordered 50 m and used 42 m"
- Phase-matched sets: Order U/V/W/PE as a matched set — we cut all four to the same length within ±5 mm and bundle-ship them
- VFD application review: For motor cables over 20 m with PWM drives above 4 kHz, our engineering team reviews capacitance, dv/dt, and reflected wave risk — and recommends output reactors if needed