UNDERGROUND DISTRIBUTION LINES USING POWER CABLE IN AN ELECTRIC DISTRIBUTION SYSTEM

UNDERGROUND DISTRIBUTION LINES USING POWER CABLE IN AN ELECTRIC DISTRIBUTION SYSTEM

How are power cables being used in an electrical distribution system?

Underground distribution lines have been a long known technology used by many electric utilities in delivering power to its customers. This set up can usually be found in highly urbanized areas where space for overhead lines can be scarce. Various pros and cons are known to be associated in using underground distribution lines in a power distribution system.

Like any other construction which involves public or private area, distribution system using underground lines installation must at all times coordinate with the installation master plan of the city or with any private properties to avoid conflict with construction of future facilities.

For easy access for inspection and maintenance, underground lines are normally installed adjacent to roadways in urban, housing, or industrial plant areas, but may be routed as required to meet the project objectives.

A careful study will be made of all underground utilities in order to ensure a minimum of interference between electrical lines and other underground utilities, whether existing, being constructed, or proposed as a definite future construction project. Electrical lines will be at least six feet from any steam or hot water lines, except at crossings where a one-foot separation from such lines is adequate.

In designing underground distribution system, electric utilities must follow or comply necessary requirements to insure the installations are within standard. Symbols and codes must be in accordance with the standards to avoid misinterpretations caused by different symbols used.

Underground cable systems may employ manholes or above-ground sectionalizing and pulling cabinets depending on local geological conditions, potential for damage from vehicles and the required design life of the facility.

All secondary underground cables may be installed in either concrete encased ducts or direct burial type ducts or conduit, or they may be direct burial type cables. Direct burial plastic conduit may be utilized when cable temperature conditions are within the conduit rating and where the conduit is not under large paved areas or building structures. Conductors shall be copper, although aluminum may be used in lieu of copper conductors No. 4 AWG and larger.

When it comes to cable installation, all primary underground cables shall be installed in concrete encased non-metallic ducts or concrete encased galvanized rigid steel conduits except as follows. Steel conduit, which is not concrete encased, shall be corrosion proof-coated (PVC, etc.) and shall be employed only for short runs between buildings or under paved areas. Direct buried ducts or direct buried cables may be employed for primary distribution (above 600 V) feeders located in areas which are remote to normal pedestrian and vehicle traffic.

 Consider using a direct buried, flexible polyethylene cable, duct type conduit with self contained cable to allow easier replacement. Concrete markers shall be provided at approximately 200 foot intervals and at each change in direction to indicate the location of underground cable route. Direct buried cable or cable duct, which is not concrete and metallic conduit encased, should be marked with a metallic/magnetic warning tape buried six to twelve inches below the surface and above the cable or duct. Cable warning tape shall be red or orange in color.