Industrial Wireless Bridge Replaces Festoon Cables for Crane Control

The Challenge: Festoon Cable Failures in Steel Mill Cranes

A steel plant with an annual output of 6.5 million tons of high-quality steel operates three 125-ton double-girder overhead cranes in the scrap yard. These cranes transport scrap steel and hot metal ladles to the converter bay. Each crane has a Siemens S7-1200 PLC in the operator cabin at 28m height, while the ground control system uses an S7-1500 PLC in the electrical room at ground level. The original setup relied on a 200m festoon cable combined with a conductor rail for centralized control.

The festoon system caused persistent problems:

• Core breakage and insulation damage every 3–6 months, leading to an average downtime of 2.3 hours per month.
• Loose connectors due to high temperature and vibration in the cabin, causing intermittent signal loss that was difficult to diagnose.
• No spare capacity for additional signals—adding anti-collision and weighing functions would require 30 more cores, but the cable tray was already full.

The plant needed a wireless alternative that could handle bidirectional discrete signal transmission over 300 meters, with packet loss ≤0.1% and minimal power consumption.

Wireless Bridge Solution: Key Features

The selected industrial wireless bridge operates in the 2.4 GHz or 5.8 GHz bands, with adjustable transmit power from 100 mW to 500 mW. It is designed for harsh environments with the following specifications:

The low power design allows direct supply from the crane’s 24V auxiliary power, avoiding separate power runs. The integrated digital I/O terminals eliminate the need for additional remote I/O modules, simplifying wiring and reducing cost.

Implementation Steps

Site Survey: A handheld test kit measured RSSI at -48 dBm between the cabin (28m high) and the ground electrical room, with a link budget margin >20 dB using a 2 dBi antenna. This confirmed a reliable connection.

Mounting: On the crane, the wireless module was DIN-rail mounted inside the cabin’s maintenance box, with the antenna extended via SMA cable to a 1.5m fiberglass pole on the roof. On the ground, a 2m pole was installed outside the electrical room, positioned more than 1 meter away from high-voltage conductor rails to avoid interference.

Wiring: Both PLCs connected via their Ethernet ports to the LAN ports of the wireless bridges. Sixteen discrete signals—emergency stop, overload, limit switches—were wired directly to the crane-side DI terminals. The cabin alarm light was connected to a DO. On the ground side, DO terminals controlled a sounder/beacon, and DI terminals received call signals from the converter operator.

Configuration: The pair came pre-paired from the factory; only the SSID and password needed to match. The PLC network remained on the original 192.168.0.x/24 subnet, so no program changes were required.

Testing: A 72-hour continuous ping test resulted in zero packet loss out of 300,000 packets. The SCADA system refreshed every 100 ms, with no delay in crane start/stop or fault signals.

Results and Benefits

After six months of operation, the three cranes eliminated cable replacement costs of approximately $6,400 (USD equivalent) and reduced production losses by 1,200 tons. The total annual economic benefit was estimated at $52,000. Additionally, removing the festoon cable improved ventilation in the cabin, lowering the summer temperature by about 5°C and enhancing operator comfort.

Scalability and Future-Proofing

The wireless bridge architecture is inherently scalable. If the plant later adopts 5G or fiber optic ring networks, the ground-side Ethernet cable can simply be connected to a 5G CPE or fiber media converter. This paves the way for future smart crane initiatives, such as unmanned operation and predictive maintenance, without replacing the existing wireless infrastructure.

For plants considering similar upgrades, the low power consumption, industrial-grade protection, and protocol transparency make this wireless solution a drop-in replacement for festoon cables in many crane applications. It is particularly suited for steel mills, ports, and other heavy industries where moving machinery requires reliable, maintenance-free communication.