This is the most conventional method of underground cable installation and involves the creation of a duct network to enable subsequent installation of cables by pulling, blowing or using floatation techniques. This may comprise a large main duct that contains smaller sub-ducts (for individual cable installation), a large main duct into which cables are progressively pulled one over the other as the network grows or a small sub-duct for the installation of a single cable. Duct installation provides the easiest and safest deployment method and also enables further access and reconfiguration. As with direct burial (below) consideration needs to be given to other buried services. Efficiency of cable installation in ducts relies heavily on the quality of the duct placement; this applies to all installation methods.


Necessary main elements

• Ducts and possible sub-ducts
• Duct cables
• Branch-off closures


Cables are installed into the ducts by pulling, blowing or floating. If they are to be pulled, then the duct either needs to contain a pre-installed draw-rope or to have one installed by rodding and roping. If they are to be blown in or floated, then the duct and any connections between sections of duct need to be airtight. The inner wall of the sub-duct is manufactured to ensure low friction with the cable sheath. This is typically achieved with a low friction coating. Alternatively, the sub-duct could contain a low friction extruded profile and/or special duct lubricants can be used.