How to Choose Communication Cables for IoT Applications in South Africa

Overview: Why cable choice matters for IoT

Choosing the right communication cable for IoT applications affects signal integrity, power delivery, noise immunity, and long-term reliability. Wireless sensors, edge gateways, and industrial controllers still rely on wired links for backhaul, power-over-data, or deterministic communications. This guide explains cable types (twisted pair, coax, multi-core, and shielded pairs), key specifications, and selection criteria tailored to South African makers, students, technicians, and procurement teams.

Common cable types used in IoT

Twisted pair (Unshielded & Shielded) - RS-485, Ethernet, CAN

Twisted-pair cables are the workhorse for many IoT networks. UTP (unshielded) is common for short-run Ethernet and non-critical signals; STP/FTP (shielded) or individually shielded pairs are preferred where EMI or long runs are present. Use RS-485 twisted pair for long-distance, multi-drop sensor buses and Cat5e/Cat6 for Ethernet and Power over Ethernet (PoE).

Coaxial cable - RF & some legacy links

Coax remains necessary for certain radio, GNSS, and video links. Choose the correct impedance (typically 50 ohm for antennas, 75 ohm for video) and connector (SMA, BNC, N-type) to minimise reflections and loss at the operating frequency.

Multi-core cable - sensors, control, and combined power/data

Multi-core screened cable is often used when multiple sensor signals or combined power and data are required. Look at conductor size (AWG or mm2), insulation type, and whether pairs need individual shields to prevent crosstalk.

Key specifications to check

• Impedance (ohms): Match transceiver and cable (e.g., 100 ohm for Ethernet, 120 ohm for RS-485 differential pairs, 50/75 ohm for RF).
• Capacitance and propagation delay: Important for timing-sensitive buses and high-speed Ethernet.
• Shielding (none, overall, pair): Choose based on EMI environment and distance.
• Conductor size: Thicker conductors (smaller AWG number or larger mm2) reduce voltage drop for power-inclusive runs.
• Temperature and UV ratings: For outdoor or rooftop IoT endpoints, pick UV-stable jackets and suitable temperature range.
• Connector compatibility: RJ45, M12 (industrial), screw terminals, or board-mounted headers-verify pinout and mechanical keying.

Standards and signalling basics

Match cables to the signalling standard you intend to use. Examples include 10/100/1000Base-T (Ethernet over Cat5e/Cat6), 1000Base-TX (Cat6 for higher reliability), RS-485 (120 ohm twisted pair), CAN (twisted pair with 120 ohm termination), and PoE (requires Cat5e or better for power delivery). For RF, follow impedance and frequency-specific cable choices (RG-58, RG-174, LMR series).

Quick spec comparison

Selection criteria: Step-by-step

1. Define protocol and distance: Identify whether the link is Ethernet, RS-485, CAN, or RF and measure run length. Longer runs favour differential signalling or lower-loss coax.
2. Decide on power delivery: If using PoE or combined power/data, choose Cat5e/Cat6 with adequate conductor rating and consider voltage drop using Ohm's law: V_drop = I * R (where R depends on conductor length and AWG).
3. Assess environment: Indoor vs outdoor, exposure to sunlight, chemicals, or EMI. Pick UV-rated jackets, armoured variants, or shielded pairs as needed.
4. Choose connectors and termination: For industrial sites, M12 and screw-term connectors provide robust connections; for office or building deployments RJ45 is standard.

Example calculation: Voltage drop for a PoE camera

A PoE camera draws 0.5A at 48V and is 100m from the switch using Cat5e. Approximate conductor DC resistance for 24 AWG pair is 84 ohms per km (0.084 ohm/m). Loop resistance = 2 * 100m * 0.084 ohm/m = 16.8 ohm. V_drop = I * R = 0.5A * 16.8Ohm = 8.4V. That is a significant drop; using higher-grade cabling, shorter runs, or local injectors reduces drop. In practice PoE switches compensate within spec, but check budgets and spec sheets.

Wiring diagram examples (ASCII)

Ethernet (T568B) RJ45 pinout example:
Pin 1: Orange/White    Pin 2: Orange
Pin 3: Green/White     Pin 4: Blue
Pin 5: Blue/White      Pin 6: Green
Pin 7: Brown/White     Pin 8: Brown

RS-485 simple two-wire:
[PC/Controller] ---A-----+-----A--- [Sensor]
                       |
                       +-----B--- [Sensor]

Troubleshooting common cable issues

• Link flakiness: Check pair-to-pin continuity and correct termination. For Ethernet, use a cable tester to verify all pairs.
• Intermittent noise: Swap to shielded cable or add proper grounding to shields; avoid running signal cables parallel to mains power.
• Excessive loss on RF: Confirm cable length vs frequency; use lower-loss coax like LMR-400 for longer antenna feeds.

Practical procurement & installation tips for South African projects

• Check stock levels at Samrand and branch pages before purchasing; request quotes for bulk runs (prices vary by metre and type; small-run patch leads often cost from ~ZAR 50-200 depending on type and length, estimates only).
• Ask for cut-and-test services if available for education or lab installations so you receive pre-terminated, tested leads with a VAT invoice for institutional records.
• Label and document runs: keep a simple spreadsheet of cable type, length, termination, and test results to simplify maintenance.

Final selection checklist

• Protocol & distance matched to cable impedance and loss.
• Power requirements accounted (PoE/voltage drop calculated).
• Environmental ratings (UV, temp, armoured) chosen for site conditions.
• Connector type and termination method selected for reliability and maintainability.

Sources

• Ethernet Alliance - Technical resources and recommendations
• TIA (Telecommunications Industry Association) - Cabling standards and whitepapers
• IEEE Standards - Networking and signal integrity references
• Communica product categories - Cables, connectors, and test tools