Longer Patch Cords Mean Shorter Horizontal Cable

Sometimes the total of 10 meters patch cord the cabling standards recognize are not enough. Longer patch cords are recognized by the standards when the horizontal cable is shorter than 90 meters. However for each additional meter of patch cord the horizontal cable has to be shortened more than one meter. Read on to learn more.

Parts 2 to 5 of ISO/IEC 11801 specify a maximum channel length of 100 meters. This includes 90 meters of horizontal cable and 10 meters for all patch cords in total. However, in some projects 10 meters in total for patch cords are not enough.

The standards recognize longer patch cords when the horizontal cable is shorter than 90 meters. However this does not work 1:1, meaning for each additional meter of patch cords the horizontal cable has to be just one meter shorter. The standards specify extensive formulas to calculate the exact cable length depending on the very type of cable.

Very often, IT professionals do it the easy way: In a typical worst case scenario the attenuation of a patch cord is 1.5 times higher than the attenuation of the horizontal cable, so a good rule of thumb is: “For each additional meter of patch cords take 1.5 meters of the horizontal cable off.”

When using this worst case rule of thumb one might miss one meter or the other of the horizontal cable which might be still okay according to the standards’ formulas, but one is on the safe side and doesn’t have to dig into elaborate mathematical calculations. And it doesn’t hurt to have a little more attenuation headroom. 😉