Original General Order 128

Section III

Requirements For Supply Systems

31.4     Clearance and Depths

The clearance between supply system ducts and other underground structures shall be as great as practicable. The distance between the top covering of these ducts and the pavement or other surface under which they are constructed shall be sufficient to protect the system from injury by traffic.

A.    From Foreign Substructures (Except Communication Systems)

(1)    Independently Installed: Duct systems for supply cables, when independently installed, shall be separated, where practicable from gas, water, oil, or other pipe systems or other foreign substructures, by a clearance of at least 12 inches when paralleling and by at least 6 inches when crossing.

(2)    Concurrently Installed: Duct systems for supply cables, when concurrently installed with gas, water, oil or other pipe systems, or other foreign substructures, shall be installed with the separation required by Rule 31.4-A(1) except that by mutual agreement between all of the parties involved there may be less separation for duct systems for supply cables of 0-750 volts.

B.     From Communication Systems

(1)    Independently Installed: Duct systems for supply cables when independently installed, shall be separated, where practicable from communication duct systems and buried cables or conductors by not less than 3 inches of concrete, 4 inches of brick masonry or 12 inches of earth.

(2)    Concurrently Installed: Duct systems for supply cables, when concurrently installed with communication duct systems, may be installed with less separation than required by Rule 31.4-B(1) by mutual agreement between all of the parties involved. (See Rule 41.4-B(2) )

C.     Depth

Ducts carrying supply cables and conductors shall be at a depth below the surface under which they are located to provide cover as required by the circuits they contain (See Rule 33.4) and as further determined by related circumstances described below.

(1)    Railroads: The top of supply system duct structures shall be located below the base of the lowest rail at a depth of not less than 30 inches in the case of street railroads and not less than 42 inches in the case of other railroads.

Where these depths are not practicable, or for other reasons, they may be reduced by agreement between the parties concerned. In no case, however, shall the top of the duct protection extend higher than the bottom of the ballast section which is subject to working or cleaning.

(2)    Thoroughfares: Supply duct systems in thoroughfares shall be installed with not less than 24 inches of cover. Where it is not practicable to obtain such cover, it may be reduced provided the duct material itself, or additional top protection installed, has sufficient strength to protect the duct system from injury by traffic.

(3)    Sidewalks and Parkway Areas: Ducts carrying supply cables under sidewalks or parkways shall have not less than 12-inch cover when containing circuits energized at 750 volts or less, and not less than 24-inch cover when containing circuits energized in excess of 750 volts. In either instance the minimum cover may be reduced if adequate mechanical protection is provided.

(4)    Private Property: Ducts carrying supply cables and conductors on private property shall have not less than 12-inch cover when containing circuits energized at 750 volts or less, and not less than 24-inch cover when containing circuits energized in excess of 750 volts. In either instance the minimum cover may be reduced if adequate mechanical protection is provided.

(5)    Open Ditches, Bridges, Trestles, Viaducts, and Similar Structures: Supply systems shall be provided with suitable mechanical protection when suspended across an open ditch or when carried on, in, under, or on the side of a bridge, viaduct, trestle or similar structure.

Supply systems suspended below or at the side of bridges shall be adequately supported at suitable intervals to suspend safely the combined weight of the cable and conduits.

Conduit and ducts shall be provided with expansion couplings or other means of compensating for the contraction, expansion, or other movement of the duct system or of the bridge or other supporting structure.

D.    Maintaining Clearances And Depths

(1)    Any person or agency performing surface or subsurface construction in the vicinity of supply duct systems is enjoined to maintain the minimum clearances from, and the depths of, the existing systems as required by these rules.

(2)    If minimum clearances and depths cannot be maintained, then the person or agency causing changes is enjoined to notify the owner of the duct system.

(3)    Under the provisions of this rule, a previously installed system may be maintained with less than the top cover required by other applicable rules of this section provided the system is protected in accordance with Rule 33.4-D(1).