See rule 12-012 (13)
It refers to CSA standard C22.3 No.7 and because the reference is a code rule then by extension the standard becomes a compulsory part of the Electrical code for any installation that the other 12 rules do not define. In easy English if the trench is shared with other utilities on the incoming side or to an outbuilding on the consumer side then the other stuff buried must follow the Standard.
Another $175 dollar code document or just stay 300 mm away from water and sewer and gas and don't cross other services except at right angles. Electric crosses lower than sewer since sewer must be graded. Table 53 tells minimum depth of burial.
