Detailed Description
Signal vs Power — Why Separate Cables
On a factory overhead crane, the signals controlling the crane are more numerous — and more critical to safety — than the power driving the motors:
| Circuit | Core Count | Signal Type | Criticality |
|---|---|---|---|
| Hook upper limit switch | 2 (NC) | 24 V DC dry contact | Safety — prevents overwind |
| Hook lower limit switch | 2 (NC) | 24 V DC dry contact | Safety — prevents rope unspooling |
| Trolley end stop x2 | 4 (2×NC) | 24 V DC dry contact | Safety — prevents bridge collision |
| Brake release | 2 | 230 V AC relay | Operational — prevents brake drag |
| Encoder feedback | 2–8 pairs | 5–24 V DC digital pulse | Control — VFD closed-loop |
| Load cell | 1–2 pairs | mV-level analog | Operational — weighing |
| Motor thermal sensor | 2–4 | PTC or PT100 | Protection — prevents overheating |
| Emergency stop | 2 (NC) | 24 V DC | Safety-critical — stops all motion |
| Pendant station | 6–12 | 24 V DC push-button | Control — operator interface |
A total of 23–38 conductors — far more than the 4–8 power conductors. The signal cable is typically the larger of the two cables by core count, though smaller by diameter due to the lower current rating (0.34–2.5 mm² vs 4–70 mm² for power).
Shielded Pairs — The Encoder and Load Cell Requirement
Incremental encoders and load cells generate low-voltage, high-frequency signals that are susceptible to electromagnetic interference from adjacent power cables:
- Encoder: 5–24 V DC square-wave pulses at 1–100 kHz — induced noise causes false counts and position error
- Load cell: 0–20 mV DC analog at bridge excitation — induced noise directly adds to the measured weight
Each shielded pair is individually shielded — a shared overall shield would couple noise from one pair to another within the same cable.
Flat or Round — The Installation Decision
| Flat Signal Cable | Round Signal Cable | |
|---|---|---|
| Best for | Festoon systems | Reeling drums, conduit |
| Loop behavior | Stable — no twist | Can twist, needs guided festoon |
| Core count capacity | Up to 24 cores | Up to 36 cores |
| Drum packing | 30–50% more per width | Standard |
| Cable gland | Requires flat-specific gland | Standard round gland |
The flat configuration is preferred for most overhead crane applications — the signal cable typically runs on the same festoon system as the power flat cable, and the flat profile ensures clean loop formation. Round is specified for cable reel applications or where the cable is routed through conduit or flexible tubing on the crane bridge.