Code of Massachusetts Regulations
220 CMR - DEPARTMENT OF PUBLIC UTILITIES
Title 220 CMR 126.00 - Underground Electric Supply And Communication Lines 50,000 Volts And Below
Section 126.35 - Direct Buried Cable

1. Cables should be located so as to be subject to the least disturbance practical. Cables to be installed parallel to other subsurface structures should not be located directly over or under other subsurface structures, but if this is not practical, the rules on clearances in 220 CMR 126.35(3) should be followed.

2. Cables should be installed in as straight and direct a line as practical. Where bends are required, the minimum radius shall be sufficiently large to prevent damage to the cable being installed.

3. Cable systems should be routed so as to allow safe access for construction, inspection and maintenance.

4. The location of structures in the path of the projected cable route shall, as far as practical, be determined prior to the trenching, plowing or boring operation.

1. Swimming Pools. Supply cable shall not be installed within five feet of a swimming pool or its auxiliary equipment.

2. Buildings and Other Structures. Cable should not be installed directly under building or storage tank foundations. Where a cable must be installed under such a structure, the structure shall be suitably supported to prevent transfer of a harmful load onto the cable.

3. Railroad Tracks. The installation of cable longitudinally under the ballast section for railroad tracks should be avoided. Where cable must be installed longitudinally under the ballast section of a railroad, it should be located at a depth of not less than 60 inches below the top, of the rail.

Where a cable crosses under railroad tracks, the same clearances indicated in 220 CMR 126.32(1)(e) shall apply.

4. Highways and Streets. The installation of cable longitudinally under traveled surfaces of highways and streets should be avoided. When cable must be installed longitudinally under the roadway, it should be installed in the shoulder or within the limits of one lane of traffic if practical.

5. Submarine Crossings. Submarine crossings should be routed and/or installed so they will be protected from erosion by tidal action or currents. They should not be located where ships normally anchor.

1. Where a cable crosses under another underground structure, the structure shall be suitably supported to prevent transfer of a harmful load onto the cable system.

2. Where a cable crosses over another underground structure, the cable shall be suitably supported to prevent transfer of a harmful load onto the structure.

3. Adequate support may be provided by installing the facilities with sufficient vertical separation.

4. Adequate vertical clearance shall be maintained to permit access to and maintenance of either facility without damage to the other. A vertical clearance of 12 inches is, in general, considered adequate but the parties involved may agree to a lesser separation.

1. Plowing in of cable in soil containing rock or other solid material should be done in such a manner that the solid material will not damage the cable, either during the plowing operation or afterward.

2. The design of cable plowing equipment and the plowing-in operation should be such that the cable will not be damaged by bending, side-wall pressure or excessive cable tension.

1. Minimum burial depths shall be as indicated in 220 CMR 126.35(4)(d)1. Table 1:

Table 1

CONDUCTORS OR CABLES

2. In areas where frost conditions could damage cables, greater burial depths than indicated above may be desirable.

3. When lesser depths than indicated above cannot be avoided, adequate supplemental protection shall be provided.

4. Where the surface under which a cable is to be installed is not to designated final grade, the cable shall be placed so as to meet or exceed the requirements indicated above, both at the time of installation and subsequent thereto.

1. Voltage. Grounded supply systems shall not be operated in excess of 22,000 volts to ground. Ungrounded supply systems shall not be operated in excess of 5300 volts phase to phase.

2. Bare Grounded Conductor. A supply facility operating above 300 volts to ground must include a bare grounded conductor in continuous contact with the earth. This conductor, adequate for the expected magnitude and duration of the fault current which may be imposed, shall be, one of the following: a sheath and/or shield; multiple concentric conductors closely spaced circumferentially; a separate bare conductor in contact with the earth and in close proximity to the cable where such cable or cables also have a grounded sheath or shield not necessarily in contact with the earth. The sheath and/or shield as well as the bare conductor shall be adequate for the expected magnitude and duration of the fault currents which may be imposed.

Note: This is applicable when cable in non-metallic duct is considered as a direct buried cable installation and random separation is desired.

Exception: Where a buried cable passes through a short section of conduit, such as under a roadway, the contact with earth of the grounded conductor can be omitted, provided the grounded conductor is continuous through the conduit. The bare conductor(s) in contact with the earth shall be of suitable corrosion-resistant material.

3. Ungrounded Supply Systems. Cables of an ungrounded supply system operating above 300 volts shall be of effectively grounded concentric shield construction in continuous contact with the earth. Such cables shall be maintained in close proximity to each other.

1. Supply circuits operating above 300 volts to ground or 600 volts between conductors shall be so constructed, operated and maintained that when faulted, they shall be promptly de-energized initially or following subsequent protective device operation. (Phase-to-ground faults for grounded circuits, phase-to-phase faults for ungrounded circuits.)

2. Ungrounded supply circuits operating above 300 volts shall be equipped with a ground fault indication system.

3. Communication protective devices shall be adequate for the voltage and currents expected to be impressed on them in the event of contact with the supply conductors.

4. Adequate bonding shall be provided between the effectively grounded supply conductor(s) and the communications cable shield or sheath. (Preferably at intervals not to exceed 1000 feet.)