CSA C22.3 No. 7:20 Underground systems.
7.1.2 Plowing of cables Supply and communication cables may be buried by plowing individually or simultaneously, provided that the minimum separations and depths of burial are in accordance with the requirements of Clauses 5.1 and 6.1. 7.2 Cable trench Trenches shall be as straight as can reasonably be achieved. The bottoms of the trenches shall be clean and free of any projecting stones. A bedding of backfill free of damaging particles below and over the cables may be used. In rocky ground or shale, cables shall be a) installed in a duct or bedding of backfill free of damaging particles at least 75 mm above and below the cables; or b) provided with an outer covering that protects the cable from mechanical damage, such as a metallic armour or an extruded polymeric layer that is specifically designed to withstand a direct- buried application on rocky ground in accordance with the cable manufacturer’s guidelines. Ridges or sharp changes in grade along the trench bottom shall be avoided where a pressure point on the cable or duct can result. When crossing other trenches or locations where earth settlement is likely, the trench bottom shall be well compacted, or some type of mechanical reinforcement shall be used to minimize future cable movement. 7.3 Mechanical protection 7.3.1 General Except as otherwise specified in Clause 5.1.5, mechanical protection for cables shall be used where a) reduced depth of burial is required; or b) deep digging is likely to occur. 7.3.2 Installation of mechanical protection General Mechanical cable protection, when in flat form, shall extend at least 50 mm beyond cables or ducts on each side. Where practical, flat mechanical protection shall not be in direct contact with the cables or ducts, but shall be separated by at least a 75 mm layer of backfill. The material used shall not corrode or react with the cable or duct material. The dimensions and type of material used shall be such that it does not fracture during installation or after backfilling.CSA C22.3 No. 7 pdf download.