A pothead is a type of insulated electrical terminal used for transitioning between overhead line and underground

high-voltage cable A high-voltage cable (HV cable) is a cable used for electric power transmission at high voltage. A cable includes a conductor and insulation. Cables are considered to be fully insulated. This means that they have a fully rated insulation system t ...

or for connecting overhead wiring to equipment like

transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...

s. Its name comes from the process of potting or encapsulation of the conductors inside the terminal's insulating

bushing Bushing may refer to: *Bushing (bearing), a type of plain bearing *Bushing (electrical), an insulated device that allows a conductor to pass through a grounded conducting barrier *Bushing (isolator), a mechanical device used to reduce vibrational ...

Description

Potheads are used where higher-voltage power lines go underground, generally voltages of 600 volts or greater. They are used mostly for

service drop In electric power distribution, a service drop is an overhead electrical line running from a utility pole, to a customer's building or other premises. It is the point where electric utilities provide power to their customers.Carson Dunlop "Elec ...

s for commercial and industrial buildings. For lower voltages such as those used for residential service drops, another weather seal called a

weatherhead A weatherhead, also called a weathercap, service head, service entrance cap, or gooseneck (slang) is a weatherproof service drop entry point where overhead power or telephone wires enter a building, or where wires transition between overhead a ...

is used. The device consists of a molded plastic housing that attaches to the end of an

electrical conduit An electrical conduit is a tube used to protect and route electrical wiring in a building or structure. Electrical conduit may be made of metal, plastic, fiber, or fired clay. Most conduit is rigid, but flexible conduit is used for some purpos ...

that carries the underground cables up the utility pole to the crossarm. Multiple

insulators Insulator may refer to: * Insulator (electricity), a substance that resists electricity ** Pin insulator, a device that isolates a wire from a physical support such as a pin on a utility pole ** Strain insulator, a device that is designed to work ...

project from the plastic body, each ending at an electrical terminal. Each overhead wire is connected to a bushing terminal from which the current passes through a rod down the center of the bushing to the interior of the housing, where it is connected to a wire from the conduit. Thus the device allows the overhead conductors to pass into the conduit while serving as a seal to keep out water. The purpose of the bushings, which have corrugations moulded into their surfaces, is to provide enough

creepage distance An electrical insulator is a material in which electric current does not flow freely. The atoms of the insulator have tightly bound electrons which cannot readily move. Other materials—semiconductors and conductors—conduct electric curren ...

along their surface to prevent leakage current from the high voltage terminal from flowing to the grounded metal conduit.

Superseded

Pothead was once defined in

Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operation ...

(IEEE) Std 48-1962 "Standards for Potheads." This standard was superseded by IEEE Std 48-1975 "IEEE Standard Test Procedures and Requirements for High-Voltage Alternating-Current Cable Terminations," and "pothead" was dropped from usage. The current standard is IEEE Std 48-2009. What was once called a pothead is now called a "Class I High-Voltage Cable Termination," which must meet these requirements: # Electrical stress control # Insulation between the conductors and ground # An environmental seal

Alternatives

Formerly, medium- and high-voltage cables (from about 2.5 kV and above) were terminated with hand-made "stress cones" composed of multiple layers of insulating tape, semi-conductive tape, and insulating putty. By tapering the layers of tape carefully, the potential gradient from the inside of the cable to free air was reduced so as not to cause

electrical breakdown Electrical breakdown or dielectric breakdown is a process that occurs when an electrical insulating material, subjected to a high enough voltage, suddenly becomes an electrical conductor and electric current flows through it. All insulating mate ...

and tracking along the surface of the termination. Current practice for these terminations is to use a pre-molded rubber stress cone, which can be slipped over the cable end and shrunk to fit snugly around the exposed cable insulation. This saves considerable installation labor and reduces the chance of errors.D.J. Littler(ed), ''Electrical Systems and Equipment: Incorporating Modern Power System Practice Third Edition'', Elsevier, 2014, page 540 High voltage terminations conforming to IEEE Std 48-1990 and not requiring potting compound are illustrated below:

References

{{reflist Electrical components Electric power distribution

Description

Superseded

Alternatives

See also

References