Cable Lengths Are a Design Deliverable, Not a Field Guess

Behind the scenes on a recent command center project: the drawings showed where every display, desk and rack goes. They did not say how long each cable had to be.

So before we priced anything, we did a takeoff.

How we measured

• We scaled each run off the floor plan, rack to device.
• We added the vertical: up out of the rack, across the ceiling, back down.
• We added the service loop the drawing notes call for.
• Then we added 25 percent on top for conduit routing, bends and the unknowns nobody sees until the ceiling is open.

What a quick estimate would have missed

First, the active optical display cables only come in fixed sizes: 33, 50, 66, 98 and 131 ft. There is no 82 ft cable, so every run that landed between 66 and 98 ft got priced at 98.

Second, we checked that every signal actually reaches. Network runs stay well inside the 100 m channel limit, USB extension runs inside the extender rating, and the desk monitor runs go back to the datasheet for bandwidth.

It is a few hours of desk work. It is cheaper than a change order.