What is cable crossing installation?
Where an AGL cable has to cross a runway, taxiway or another service, it goes through ducts laid beneath the surface, with spare ways and a handhole on each side, so cable can be installed and replaced without cutting the pavement again.
A cable crossing is built wherever an AGL cable has to pass a runway, taxiway, road, drain or another buried service. Across a pavement the cable goes through ducts laid beneath the surface, usually encased as a duct bank, with a handhole or pit on each side. The ducts are laid from the design, with spare ducts and a draw rope in every way, and the cable is pulled in afterwards. See the series-circuit view of Cable Crossing.
A crossing is only cheap to get right while the trench is open. A wrong line, depth or separation from another service, or a duct that is crushed or blocked, means cutting the operational surface again or a cable that cannot be pulled. Locate existing services before digging, keep other services clear as the design requires, cap the spares, place warning tape above and record the as-built route. Treat any cable as live until the circuit has been isolated, locked out and proved dead, and work to the airport’s permit-to-work and any pavement closure.
- Locate. Find and mark existing services and confirm the route and depth against the design and as-builts.
- Route. Set out the crossing from the design, as straight as it allows and clear of other services.
- Duct bank. Excavate and lay the ducts to the design depth, with the specified encasement and falls.
- Spares and ropes. Include the spare ways in the design, fit a draw rope in each duct and cap the ends.
- Protect and mark. Lay the warning tape above, backfill and reinstate the surface as specified.
- Record. Log the as-built route, depth, duct positions, handholes and spares, with photos before backfill.
Frequently Asked Questions
Q1What is a cable crossing in AGL installation?
The place where an AGL cable has to cross a runway, taxiway, road, drain or another buried service. Across a pavement the cable runs through ducts laid beneath the surface, with a handhole or pit on each side for pulling, so the cable can be installed and later replaced without cutting the pavement again.
Q2Why are crossings built with spare ducts?
Because breaking into an operational pavement is slow, costly and disruptive. Spare ducts, capped and fitted with draw ropes, let future cables be added or a failed one be replaced by pulling, not digging. The number of spare ways is set by the design.
Q3How is a crossing different from ordinary cable routing?
Ordinary routing lays cable in an open trench on a bed with cover and warning tape. At a crossing, the cable usually goes through ducts, often encased, because the surface above must not be disturbed later. The route, depth, separation from other services and ends of the ducts are all taken from the design.
Q4What should be checked before digging a crossing?
Locate and mark existing services, confirm the route and depth against the design and as-builts, and obtain the airport’s permit-to-work and any closure needed. Treat any cable found as live until the circuit has been isolated, locked out and proved dead.
Q5What records should be kept for a crossing?
The as-built route, depth, number and position of ducts and spare ways, the position of handholes or pits at each end, and photographs taken before backfill. These make the crossing findable and usable years later.
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