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g/av • Posted by u/rack_randy •

Rack build for a 400-seat lecture hall — cable management before and after Install

University lecture hall, twenty years of accumulated AV in one rack. Rebuilt it over a semester break.

What I changed structurally, not just cosmetically:

Horizontal lacing bars instead of D-rings. D-rings force you to route in bundles, and a bundle means pulling one cable disturbs eight. Lacing bars let every cable have its own path with a service loop.

Power on the left, signal on the right, crossings at 90 degrees only. This is not superstition, it is measurable — we had audible hum in the old rack that vanished.

Every cable labeled at both ends with the same scheme as the drawings. Sounds obvious. The old rack had labels in three different schemes from three different contractors and none of them matched the as-builts.

Service loops at every termination. Two feet minimum. The next person to work on this needs to be able to pull a piece of gear forward without unplugging its neighbors.

The whole rebuild took nine days. The install itself was maybe three. The other six were tracing what the previous twenty years had actually done, because the documentation was fiction.

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u/av_wizard •

Six days of tracing and three days of installing is the honest ratio on any rebuild and nobody ever budgets it that way. If you quote a rack rebuild off the install time you will lose money on every one.

The power-left signal-right thing is worth repeating for anyone who thinks it is aesthetic. You measured a hum going away. That is an actual induced noise problem solved by geometry.

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u/rack_and_stack_rob •

Lacing bars over D-rings, completely agree, and I will add the reason it matters most: serviceability under time pressure. At 2am with a room down, the difference between a bundle and individual paths is whether you can swap a device in ten minutes or forty.

Cable management is not tidiness. It is your future response time.

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u/dante_dave •

The labeling scheme matching the drawings is the one everybody breaks. Three contractors, three schemes is so normal that I have started treating "adopt the existing scheme or replace it entirely, but do not add a fourth" as a rule.

If the existing scheme is bad, relabel everything. Half-relabeling is worse than either option.

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u/crestron_carl •

Nine days over a semester break is exactly the right way to schedule this and getting that window is usually harder than the work. Universities have precisely two windows a year and if you miss one you are living with the old rack until January.

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u/fiber_fred •

Service loops at every termination — two feet is right for AV. On fiber I go longer, because a fusion splice needs enough slack to reach a splice tray on a cart, and the guy repairing a broken fiber at 3am does not have the option of "just move the rack forward."

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