Liebherr Mining International (Newport News, Va.) builds big trucks—really big trucks. Its T 282 mining truck is the world's largest two-axle electric-drive haul truck. The vehicle has a capacity of 400 tons, stands 24.25 ft (7.4 m) tall, and is 47.5 ft (14.5 m) long by 28.6 ft (8.7 m) wide. With an unloaded weight of 448,000 lbs, the T 282 comes in with an impressive payload to empty-vehicle-weight ratio of 1.8:1.
In addition to its incredible size, Liebherr Mining engineers also designed the truck with an optimal cabin. The T 282 offers many amenities often found in recreational vehicles such as computerized instrumentation in addition to climate controlled heat and air-conditioning.
One of the T 282's major selling points is economy of operation, but Liebherr faced an economic challenge in building it. The original design required the truck use twenty 482 Series high performance thermal circuit breakers, from E-T-A Circuit Breakers (Prospect, Ill.), mounted in a dashboard unit. These breakers protect all electrical systems including computer instrumentation, exterior and interior lighting systems, relays, power supplies, and cabin components. With the T 282 in continuous operation 24 hours a day, the only downtime is for change of drivers, refueling, and maintenance. Thus round-the-clock, the truck requires circuit protection that can withstand high vibration and extreme temperature variance.
However, during installation, wiring took Liebherr Mining nearly three weeks to complete. In addition, the unit was bulky and aesthetically unappealing. But because of increased demand for production, the company needed a reduction in assembly time. Liebherr contacted E-T-A Circuit Breakers engineers to create a power distribution unit (PDU) that reduced installation time and increased capabilities while decreasing space consumption.
The E-T-A team recommended the company's 482 high performance circuit breaker. Used in some of the most critical applications, such as military aircraft and tanks, the 482 is rated for 10G vibration from 10 to 2,000Hz. The device operates with thermal circuit breaker technology, which allows for high arcing temperatures. In addition, the 482 is comparatively small and dense " offering the highest current rating and performance in the least amount of space.
Once those challenges were solved, there was still the issue of decreasing assembly time. The recent trend toward outsourcing power distribution units has resulted in saving time and money for OEMs, and this was no exception: E-T-A was able to cut the assembly time of the PDU from three weeks to one day. The PDU is equipped with a multi-socketed connector, and the wiring from the truck terminates in a mating connector, for quick and easy installation
The unit is installed behind the driver's seat. This space allows for an additional eight circuit breakers for a total of 28 per PDU. The extra breakers allow the T 282 to offer cabin accessories such as a CD player. In addition, the extra space allows for auxiliary contacts: when a breaker trips, a light appears on the dashboard indicating which circuit breaker tripped.
Ken Cybart is Senior Applications Engineer for E-T-A Circuit Protection & Control