Reeling and festoon cable for crane and trolley duty

Why flex cable is built differently

Ordinary building wire is stranded in layers, with the outer layer longer than the inner ones. Flex cable uses a bunched or rope-lay stranding where the strands are twisted together first and then cabled, so every strand travels the same distance when the cable bends. More, finer strands carry that idea further: the same copper area in smaller strands bends more times before a strand work-hardens and cracks.

The jacket matters as much as the copper. Flex jacket compounds are formulated to flex without cracking, and the cable usually carries no filler that could abrade the insulation from inside. Flat festoon cable goes further, molding the conductors side by side in a ribbon so the bend happens in one plane and the cable lies in a track without twisting.

Festoon loops and where they fail

A festoon system hangs cable in loops from trolleys in a C-track along the crane runway or bridge. As the crane travels, each loop opens and closes, and the cable bends through a radius at the bottom of the loop twice per cycle. That repeated bending is the whole duty, and it is why the loop is where the cable dies.

Failure is gradual and visible. The jacket crazes at the loop bottom, then cracks, then the strands under it break one at a time rather than all at once. A cable with a broken strand still conducts and still looks serviceable until the remaining strands heat. Anyone assessing a festoon lot should look at the loop radius marks along the length, because a cable that has been trained in a track keeps those marks long after it comes off.

Cleveland and Canton crane bays

Canton and Massillon run forging and heat-treat shops with rail-served bays and overhead cranes working continuously, and the cable on those cranes is replaced on a maintenance cycle rather than when it fails. Stark County shops often keep a spare coil on a shelf, which is how usable cable ends up in a crib with no machine to go with it.

Cleveland's steel finishing and heavy fabrication bays have the same pattern at a larger scale, with runway conductors and festoon systems on the bridge and trolley. A mill that rebuilds a crane will pull the whole festoon run at once, and the retired cable arrives as a long coil with the loops still trained into it.

• Jacket crazing at the loop radius, not just at the ends
• No broken strands visible where the jacket has cracked
• Cable still coiled in its running shape, not knotted
• Coil tagged with the crane and the date it came off

How a crane cable lot is judged

Footage matters less here than it does for building wire. A festoon run is cut to the crane's travel, so the retired cable is the length the crane needed, and that length rarely suits anything else. What makes the lot worth reviewing is the condition along the length and whether a matching spare exists.

New flex cable in original wrap is the cleanest outcome and turns up more often than people expect, because maintenance stores buy a spare and then the crane is replaced. Used cable is judged on jacket and strand, and a coil that holds a kink from a bad rewind has lost most of its value.