When the engineers involved in refurbishing the Stillwater Bridge needed a reliable signal cable to control the bridge’s vertical lift span—after the originally specified cable failed—they called upon Northwire, Inc. The lift span of the highway bridge, which crosses the St. Croix River and connects Minnesota and Wisconsin, is raised and lowered at least 20 times a day during navigation season, and the cable that controls it is unwound and rewound as many times. The Northwire-designed high-flex-life multiconductor cable fit the bill.
“We originally employed another manufacturer’s electrical control cable in the refurbishing project, but it failed within six months due to incorrect design, causing the lift span not to function and necessitating a temporary and costly ad hoc remedy,” says Bob Quist, project manager, A.A. Hanson Electric in Osceola, WI. “We asked Northwire—a hometown company—to design a new control cable.
“Northwire visited the site, designed a solution, provided the design to the Minnesota Department of Transportation, got approval and produced the cable—all within three weeks,” says Quist. “The process took months for the original cable. We were very pleased with Northwire’s turnaround, and the smaller-diameter cable is more flexible and winds more easily than the originally specified bigger cable.”
The Northwire cable is one-third smaller than the previous cable. The new cable insulation is comprised of Hytrel from DuPont, which accounts for its high-flex life properties.
From 10,000 to 20,000 cars pass over the bridge each day. From mid-May through mid-October, the bridge’s lift operates on a regular schedule when boat traffic is present. Outside of the regular lifting season, the bridge is raised upon request.