[MEP Center Engineering]

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In an office floor, the farthest work outlets are about 85 m along the cable route from the floor distributor. The design uses Cat6A U/UTP cables, many with PoE for access points and cameras.

• What exactly does the 100 m limit include, and how do patch cords count?
• How do I size the cable tray or conduit for a bundle of Cat6A cables?
• What separation from power cables and what bend radius should be shown on the drawings?

[MEP Center Engineering]

The 100 m is the channel: at most 90 m of fixed horizontal cable (permanent link) plus at most 10 m of patch and equipment cords in total, with up to four connections (ISO/IEC 11801-1, ANSI/TIA-568.2-D). An outlet 85 m away along the route is close to the limit once slack and vertical drops are added, so measure carefully.

Step 1: Check the length

• Route length to the outlet: 85 m.
• Add vertical drops, for example 2 × 3 m (down from the tray at the distributor and down to the outlet), plus a service loop of about 3 m at the rack. That gives about 94 m, which is over the 90 m permanent link.
• Options: move the outlet group to a consolidation point fed from a closer distributor, add a second floor distributor, or re-route. Do not rely on shorter patch cords to compensate. Standards allow longer work-area cords only with a reduced horizontal length, under defined rules.

Step 2: Size the pathway

Cat6A U/UTP outer diameter is typically 6 to 8.5 mm. Use the value from the datasheet. Example with 48 cables of 7.5 mm:

• Cross-section of one cable: π/4 × 7.5² = 44.2 mm². Total: 48 × 44.2 = 2 121 mm².
• At a 40 % design fill (TIA-569 for conduit with three or more cables; many designers also use 40 % for trays to allow growth), the required area is 2 121 / 0.40 = 5 302 mm².
• A 150 × 50 mm basket tray (7 500 mm²) is 28 % full, which leaves room for future cables.

Step 3: Bend radius, separation, PoE

• Minimum bend radius for installed U/UTP is 4 × the outer diameter, about 30 mm here. Specify pull-box and conduit-bend sizes to match.
• Separation from power: EN 50174-2 and TIA-569 give separation distances that depend on the cable type, the type of barrier and the power circuits. Show a metal divider or a separate tray, and crossings at 90°, rather than a generic distance on the drawings.
• PoE heats the bundle. With Type 3 and Type 4 PoE (up to 60 W and 90 W at the source), keep bundles small or use open baskets, and follow the cable manufacturer’s derating (ISO/IEC TS 29125, TIA TSB-184-A).

What to show on drawings

• Floor distributor locations with the 90 m radius checked along routes, not as a circle on plan.
• Tray sizes with the fill percentage, and the number of outlets per room.
• Labelling scheme and the test standard (permanent link test to Class E_A / Category 6A).

Common mistakes

• Measuring 90 m on plan and forgetting drops and slack.
• Filling trays to 100 % on day one.
• Running data and power in one unsegregated tray to save space.

See also Cable Tray Sizing: Fill, Spacing and Derating and MEP Drawing Standards: Layers, Sheet Numbers, Title Blocks.

For deeper study: MEP Center online certified courses.

Check the edition of the code that applies to your project.

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