Two rack ports are three meters apart. A three-meter cable looks like the obvious order—until the installation route goes up to an overhead tray and back down.

For 400G AOC length selection, the useful measurement follows the planned cable path. Straight-line rack spacing is only one input. This example is a planning exercise, not an HCH installation record.

A route worksheet, not a universal allowance

Suppose a surveyed route contains these sections:

The six-meter subtotal still needs review. Identify where the survey starts and ends, how the cable leaves each connector, and where any necessary service slack will be supported. Do not add the same segment twice or apply an arbitrary percentage as a substitute for a route survey.

Ask how the supplier defines 400G AOC length: tip-to-tip, between specified reference points, or by another drawing dimension. Connector insertion can change the relationship between a quoted assembly length and usable port-to-port routing distance. Confirm this on the selected assembly drawing.

What to put on the purchase request

Send the marked route, endpoint locations and required handling space with the requested length. Ask the supplier to confirm the measurement reference and available assembly options. If the calculated requirement falls between offered lengths, review how the extra cable would be managed before selecting the longer option.

Keep service slack accessible and supported without tight coils or stress at the connector exit. Use the selected product's bend requirements; a radius from another AOC is not a verified limit for this assembly. Excess cable should not obstruct airflow or release mechanisms.

Our 400G AOC vs DAC guide covers the broader choice between cable technologies. Once AOC is selected, record the agreed 400G AOC length definition on the order so purchasing and installation use the same reference.