What is cable protection?
The layers that keep a buried AGL cable from being struck, crushed or soaked — marking tape, cover tiles, clean bedding and encased ducts — so one dig-in does not put a whole series circuit out.
Cable protection is everything done to stop a buried AGL cable from being damaged: warning tape above it, a cover tile or slab where the design calls for one, clean bedding around it, and ducts, encased where needed, under pavements and other heavy loads.
In a series circuit every light depends on the same cable loop, so one cut or crushed cable can open the circuit or cause an earth fault and take the whole circuit out of service. Most damage comes from excavation by other people, so protection has two jobs: warn the digger and take the first blow. Depth, tile type, duct size and encasement depend on the design and the standard. Keep the route recorded on the as-builts, and treat the cable as live until the circuit has been isolated, locked out and proved dead.
- Set route and depth. Take the route and depth of cover from the design.
- Bed the cable. Lay it in clean sand or fine fill, free of sharp stones.
- Add cover. Place the cover tile or slab where the design requires it.
- Mark it. Lay warning tape above, and fit route markers as the design requires.
- Inspect, then backfill. Check the protection before it is covered, since it cannot be seen afterwards.
- Test & record. Test the circuit and mark route, depth and protection on the as-builts.
Frequently Asked Questions
Q1What is cable protection in airfield ground lighting?
Cable protection is everything done to stop a buried AGL cable from being damaged: warning tape above it, a cover tile or slab where the design calls for one, clean bedding around it, and ducts, encased where needed, under pavements and other heavy loads.
Q2Why do buried AGL cables need protection?
In a series circuit every light depends on the same cable loop, so one cut or crushed cable can open the circuit or cause an earth fault and take a whole circuit out of service. Most damage comes from excavation by other people, so protection both warns the digger and takes the first blow.
Q3What is the difference between warning tape and a cover tile?
Warning tape tells someone digging that a cable is below, but it will not stop a bucket or spade. A cover tile or slab is a physical barrier that takes the first blow. They do different jobs and are normally used together where the design requires both.
Q4When are ducts used to protect AGL cables?
Beneath pavements, roads and other heavy or busy areas, normally encased as a duct bank. The ducts spread the load and shield the cable, and they let it be replaced by pulling new cable through instead of digging up the surface.
Q5How deep should a protected AGL cable be buried?
Depth of cover is set by the design drawings and the applicable standard, and can differ between open ground, pavement and road crossings. Check your project specification rather than relying on a single figure.
Q6How is cable protection checked and recorded?
Protection is inspected before backfilling, because it cannot be seen afterwards. The cable is then tested for continuity and insulation resistance, and the route, depth and protection used are recorded on the as-built drawings so later work can avoid it.
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