Microducts are small ducts used for the installation of fibre optic cables. They have a typical size ranging from 3 to 16 mm and are installed as bundles within larger ducts. Description Microducts are typically small-diameter, flexible, or semi-flexible ducts designed to provide clean, continuous, low-friction paths for placing optical cables that have relatively low pulling tension limits. As stated in industry requirements document Telcordia GR-3155 Generic Requirements for Microducts for Fiber Optic Cables, microduct products are expected to: Be compatible with existing construction designs and building configurations for both riser- and plenum-rated applications, including cable blowing apparatus. Allow cables to be safely deployed through pull lines or strings using less than 50 lbs of force, and through cable blowing techniques at typical deployment speeds of 100-200 feet per minute. Types of ducts GR-3155 states that the basic types of duct are smoothwall, corrugated, and ribbed. The selection of a particular duct design is dependent on those characteristics that are important to the end user. The need for a specific characteristic or combination of characteristics such as pulling strength, flexibility, or the lowest coefficient of friction will dictate the type of duct required. Duct options Ducts can be purchased with a variety of options or features. One such enhancement is pre-lubrication. Pre-lubricated ducts may be either permanently impregnated with anti-friction compounds or coated with liquid lubricant during manufacture (see GR-3155). This may or may not eliminate the need for supplementary lubrication when pulling cable into the duct. Before using a supplementary lubricant with a pre-lubricated duct, the user should check with the manufacturer to determine if the added lubricant is compatible with the pre-lubricated surface of the duct. Failure to do this may result in the cable seizing up rather than reducing the friction coefficient of the duct. Placement of cable As indicated in GR-3155, cable is typically placed into the duct in one of three ways: It may be pre-installed by the duct manufacturer during the extrusion process. It may be pulled into the duct using a mechanically assisted or hand-drawn pull line. It may be blown into the duct using a high air volume cable blowing apparatus. Pre-installed cable When cable is pre-installed, the duct manufacturer extrudes the duct directly over the optical cable. Tight control of the duct temperature during the manufacturing process is essential to ensure that the duct does not stick to the cable as