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site are copyright ©2004 by Neal McLain



The following definition of Joint Pole is an expanded version of the definition found in Newton's Telecom Dictionary, 18th Edition (New York: CMP Books, 2002, p. 410; reprinted by permission of Harry Newton).

Space Allocation on Joint Poles

JOINT POLE: A utility pole which supports the facilities of two or more companies.   A typical joint pole supports three facilities: electric power, cable television, and telephone.   Some joint poles also support all manner of other devices: streetlights, signs, traffic signals, seasonal decorations, fire and police call boxes, antennas, municipal communications systems, OPGW (optical ground wire) fire- and police-alarm signal wiring.

This figure illustrates the typical allocation of space on joint utility poles in the United States; the allocation is similar in Canada except that cable television and telephone are sometimes lashed to the same supporting strand.   Starting at the top and working down, facilities on the pole are allocated into three spaces: Supply Space, Safety Zone Space, and Communications Space.

Supply Space

The Supply Space is reserved for electrical supply facilities.   Most supply-space wiring consists of uninsulated conductors.   The supply space may include separate facilities operating at different voltages; for safety reasons, the highest voltages are located uppermost on the pole.

Starting at the top and working down, the facilities in the supply space are:

  • Static wire: a grounded wire at the very top of the pole intended to protect lower conductors from lightning.
  • Transmission (sometimes called sub-transmission to distinguish it from transmission lines supported by steel structures): three uninsulated conductors which carry 3-phase high voltage (typically 69 to 200 kilovolts) circuits among substations.   This circuit may be wye-connected or delta-connected; if wye-connected, a fourth conductor, called the MGN, is required...
  • MGN (multi-grounded neutral): a single uninsulated grounded conductor.   The currents in the three phases of the transmission (or sub-transmission) line are never quite equal; if they are wye-connected, the MGN carries the residual unbalance current.   At many poles, the MGN is physically grounded to a groundrod at the base of the pole.
  • Primary Distribution: one to four uninsulated conductors, frequently supported on a crossarm, which carry power from substations to pole-mounted stepdown transformers.   The primary circuit (so named because it feeds the primary winding of the stepdown transformer) may be single-phase or three-phase, and typically operates at 4 to 15 kilovolts.
  • Secondary Distribution: one or more insulated conductors, accompanied by an uninsulated grounded neutral conductor (which may be the MGN).   The secondary circuit (so named because it is fed from the secondary winding of the stepdown transformer) provides the standard 3-wire single-phase 115/230-volt electric service for residential and small commercial customers.   On special order, three-phase service and/or higher voltages can be provided for specific customers.   Secondary distribution conductors are usually twisted together in a bundle called duplex (two conductors), triplex (three conductors), or quadruplex (four conductors), although older secondary distribution circuits may consist of separate open wire conductors.
  • Stepdown transformer: an oil-cooled transformer which converts the primary distribution voltage to the secondary distribution voltage.   Most stepdown transformers are designed for single-phase operation; if a three-phase secondary circuit is required, three physical transformers are usually required, and may be mounted the same pole as shown in the photo above.

Safety Zone Space

The Safety Zone Space is an unused space separating electric supply facilities from communications facilities.

This space is specified by the National Electrical Safety Code to separate electric supply conductors from communications conductors.   Under this code, the highest cable in the communications space must be separated from the lowest electric-power conductor in the supply space by specified distances.   The separations shown in this diagram are typical, although there are numerous exceptions and special cases.

The safety zone space protects communications personnel from dangerous voltages (even if a technician "forgets" to wear a hardhat).  

Communications Space

The Communications Space contains telephone, cable television (CATV), and other communications cables.   Communications cables are insulated; however they may be enclosed in metal shields.   For safety reasons, all exposed metallic surfaces must be bonded to each other and to the MGN.

Typical communications cables include:

  • Telephone: telephone cables supported by steel strand.   Each telephone cable contains several individual copper wire pairs; a large cable may contain as many as several hundred pair.   The strand is placed under tension to prevent excessive sag; typical strand tension is a few hundred pounds, although a strand supporting a large multipair cable may be tensioned as high as 1000 pounds.
  • Cable TV: CATV coaxial cable and equipment supported by steel strand.   An expansion loop at each pole absorbs expansion and contraction caused by temperature variations.   The strand is placed under tension to prevent excessive sag; the typical strand tension is a few hundred pounds.
  • Other: just about any other type of communications circuits.   Among the more common are fire- and police-alarm wiring, traffic-signal control wiring, and closed-circuit audio or video communications circuits.   Depending on purpose and age, these circuits may utilize open-wire conductors, twisted-pair cables (similar to telephone networks), coaxial cables (similar to CATV networks), or fiber optic cables.
Communications cables are usually supported by steel strand.   The strand is a grounded uninsulated bundle of several (usually seven) galvanized high-tensile-strength steel wires.   The strand is placed under tension, and the communications cables are lashed to it.   The following sketch illustrates a strand supporting a single CATV coax cable:
Telephone and other communications cables are supported in the same manner.   A single strand can support more than one cable:


No real-world joint pole looks exactly like the archetypical pole defined above, but some come pretty close.   Following are photos of a few representative examples.

Joint Pole I

Power, CATV, Telephone,
Traffic Signals

This pole supports an enormous transmission line, probably at least 69-Kv, possibly even higher.   It also supports:
  • Primary distribution.
  • Secondary distribution.
  • CATV cables.
  • Telephone cables.
  • Traffic signals.
  • Traffic signal wiring.

The secondary distribution wiring appears to be a duplex bundle in which the MGN serves as both neutral and mechanical supporting strand.   A duplex bundle is normally used in situations where only a single 115-volt circuit is required; such circuits are typically provided for low-capacity loads such as streetlights and traffic signals.

Joint Pole II

Power, Telephone, CATV, Streetlight

This pole supports the usual three facilities: electric power, CATV, and telephone.   But note that:
  • There is no static wire.
  • The MGN is on the same crossarm as the primary conductors.
  • The pole includes an unmetered streetlight, wired directly to the secondary.
  • The CATV network is offset on a sidearm probably to maintain clearances from other facilities.


Joint Pole III

Power, Telephone,
CATV, Streetlight

This pole supports:
  • A static wire.
  • A large transmission line, probably at least 69-Kv.
  • Secondary distribution wiring (both open-wire and triplex).
  • A streetlight, hardwired directly to secondary distribution.
  • CATV cables.
  • Two telephone cables, with strand-mounted splice cases.
  • A pole-mounted telephone cross-connect panel.
Note that there is no primary distribution on this pole; the secondary voltage arrives from a transformer offscreen to the left.

Joint Pole IV

Power, Alarm Signals, CATV, Telephone, Traffic Signals

This pole supports:
  • Two primary distribution circuits.
  • One open-wire secondary distribution circuit.
  • Traffic signal wiring.
  • Fire alarm wiring.
  • CATV network.
  • Seasonal decoration.
  • Traffic signals
  • Pedestrian walk signals.

Note that the fire-alarm wiring is open wire, and that it appears to be very close to the CATV cable.   If these wires are not insulated, this would constitute a violation of the National Electrical Safety Code.

When this picture was taken, this pole supported what the National Electrical Safety Code calls a seasonal decoration.   Seasonal decorations often contain lighting circuits; these circuits are usually fed from the secondary distribution circuits on the pole.

Joint Pole V

Power, Transformer,
CATV, Telephone

On this pole, telephone and CATV cables are mounted side-by-side at the same vertical position, offset horizontally by a common crossarm.   This arrangement saves space on crowded poles while still maintaining required clearances.

Joint Pole VI

Power, Power riser, Streetlight, CATV

This pole differs from the previous examples in two ways: it's made of prestressed concrete, and it supports a riser.

Prestressed concrete poles are often used in coastal areas subject to atmospheric corrosion (one manufacturer claims that "concrete poles are foremost in appearance, durability and maintenance-free service").

A riser is an electrical connection attached to the side of a pole; hence, a pole supporting a riser is called a riser pole.   The riser provides a connection between aerial conductors and underground conductors.   The riser conductors are usually protected by conduit, although a U-guard is sometimes used.

This particular concrete pole supports:

  • Static wire.
  • A three-phase wye-connected (four-conductor) transmission circuit.
  • A three-phase primary distribution circuit, tapped to feed, via the riser, an underground circuit to a nearby large customer such as a school, hospital, or shopping center.
  • A streetlight.
  • A single-phase secondary distribution circuit (fed from a transformer offscreen to the right) whose sole purpose is to provide power for the streetlight.
  • Strand-supported CATV cable.

Joint Pole VII

Power, Transformer,
CATV, CATV Power Supply

This pole supports:
  • Three-phase primary electric distribution.
  • Transformer.
  • Single-phase secondary electric distribution.
  • Strand-supported CATV cable.
  • Pole-mounted CATV power supply.
  • Pole-mounted electric meter to provide power for the CATV power supply.

CATV networks (also calledbroadband networks) incorporate broadband amplifiers spaced throughout the network at intervals of about 2500 feet.   These amplifiers require operating power; this power (at 60, 75, or 90 volts RMS) is provided by a CATV power supply similar to the one shown here, and delivered to the amplifiers over the CATV network itself.   Each power supply is capable of powering a group of 10 to 20 amplifiers located within a radius of a mile or so.   Each amplifier incorporates a DC power pack that rectifies this voltage and provides DC operating voltages for the amplifier circuitry.

The CATV power supply receives its operating power from the power company's secondary distribution circuit, at 115 volts, 60 Hz.   Depending on the power company's billing policies, CATV power supplies may be metered, or they may be billed on a flat-rate basis.   The power supply illustrated here is metered; the meter is visible below the power supply.

The following sketch illustrates a typical wiring diagram for a metered CATV (broadband network) power supply:

Joint Pole VIII

Power, Transformers, CATV,
Telephone, Fiber Optic Cable

This pole supports a separate fiber optic cable in the communications space.   It's probably a voice- and data-communications cable owned by a telephone company.

The pole attachment clamp supports the fiber in a padded cylinder so that wind-induced vibrations do not cause the fiber to scrape against metal.   The red plastic sleeve above the clamp identifies the name of the owner and provides a contact telephone number.

Farmington, New Mexico, 2004

Joint Pole IX

Power, Telephone, CATV, CATV Power Supplies, Traffic Signal

This pole supports:
  • Three-phase open-wire primary electric distribution.
  • Single-phase triplex secondary electric distribution.
  • CATV cable for public cable TV network.
  • CATV cable for Institutional network ("I-Net"), a closed circuit coaxial network for schools and municipal government.
  • Multipair telephone cable.
  • Two CATV power supplies, one for the public CATV network and one for the I-Net.
  • Electric meter (behind the sign) to meter the power used by the two cable TV power supplies.
  • Flashing amber warning light.
  • Disconnect switch for the unmetered flashing amber light.

The I-Net is physically identical to the public CATV network (and, in fact, it was built by, and is probably still owned by, the CATV company).   However, it is connected only to governmental and quasi-governmental buildings such as City Hall and schools.

There is no electric meter for amber warning light; apparently, the owner of the light is billed on a flat rate basis.


If a joint pole is a pole "which supports the facilities of two or more
companies," then a non-joint pole is a pole owned by, and used exclusively
by, one company.   Following are four examples of non-joint poles.

A Power Pole

This pole supports transmission (or sub-transmission), an MGN, secondary distribution, and a stepdown transformer.   There are no communications cables on this pole; hence, there is no identifiable safety zone and no identifiable communications space.   It's a power-only pole.   Or just power pole.

A Telephone Pole

This pole supports telephone facilities (cables and splices) only.   There are no electric power conductors on this pole; hence, there is no identifiable safety zone space and no identifiable supply space.   Furthermore, there are no non-telephone communications facilities on this pole.   It's a telephone-only pole.   Or just telephone pole.

This the only kind of pole than can accurately be called a "telephone pole."

Hooper, Utah, 2002.

A Cable Pole

This pole supports CATV (broadband network) facilities only.   There are no electric power conductors on this pole; hence, there is no identifiable safety zone space and no identifiable supply space.

Furthermore, there are no telephone or other non-broadband facilities on this pole.   It's a cable-only pole.   Or just cable pole.

Items on this pole include:

  • Strand.
  • Amplifier.   The amplifier housing (see photo below) contains separate amplifier modules to amplify the trunk signal and to provide outputs to drive the feeder cables.   The amplifier housing also includes a power pack to accept power from the cable TV power supply and provide DC voltage to drive the amplifier modules.
  • Tap.   A tap, installed in the feeder cable provides connections for drop cables to individual buildings.
  • Fiber optic cable.   Fiber is used to transport broadband signals over distances of several miles, typically 20 to 50 miles.   Fiber cables are typically identified by red plastic identification tags bearing the name of the owner.   Fiber owned by CATV companies is usually lashed to the same strand that supports the coaxial trunk cable; at this particular pole, the fiber bypasses the amplifier to feed other portions of the network.
  • Coaxial trunk cable.   Trunk is used to transport broadband signals over distances of a few miles, typically not more than than two or three, and almost never more than ten.
  • Coaxial feeder cable.   Feeder is used to transport signals over distances of a few city blocks.   Taps are installed in the feeder at intervals of every other lot or so, to provide connections for drops to individual buildings.
  • Disconnected drop.   Drop cables are used to connect taps to individual buildings.   An active drop is connected to the tap; a disconnected drop (sometimes called dead drop) is disconnected from the tap and secured so that it cannot be reconnected except by a company employee.

A Railroad Pole

These poles are owned by, and located on property owned by, a railroad company.   These poles support three types of circuits: electric power, signalling, and communications.   All circuits are open wire, implemented with uninsulated wire.

Even though there are three types of circuits on these poles, they are still non-joint poles because all circuits are owned by the same owner.   They're railroad-only poles.   Or just railroad poles.


Electric power is distributed at 2400 volts, 60 Hz, single phase.   Stepdown transformers located near equipment shelters provide operating power for the shelters.

Signalling circuits control train-signal lights and safety equipment at grade crossings (gates, lights, bells).

Communications circuits provide voice and signal communications among equipment shelters and company offices.

Note that on this particular pole, the two conductors of one audio pair are transposed.   This procedure is used to reduce inductive crosstalk from nearby conductors.   By transposing conductors at specified intervals, it's possible to suppress crosstalk among several open-wire audio pairs installed along the same poleline.


Odd, weird, or unusual poles.

Somewhere in Massachusetts, 1992.                  

A Wall of Wires

These poles support only two facilities: electric primary and telephone cables.   A solid wall of telephone cables.
Belmont, Wisconsin, 1994.

A Pole Supporting a Microwave Antenna

This pole supports an AML (Amplitude Modulated Link) microwave receiving antenna and receiver.   This equipment receives cable television signals from a hilltop-transmitter a few miles away, and feeds them to a receiver (mounted on the pole a few feet above ground) that converts them to standard NTSC signals for distribution to the local community.

Block diagram of a typical AML receiver manufactured by Hughes Aircraft Company.   A voltage-controlled crystal oscillator (VCXO), operating at 73.956140 MHz, is phaselocked to a pilot carrier received from the transmitter in the guardband between channels 4 and 5.   The output of the VCXO is multiplied by a factor of 171 to derive the Solid State Source (SSS) frequency of 12.6465 GHz.   This frequency is then applied to a mixer, which downconverts the microwave band to the standard cable television band.

Channel assignments utilized by AML equipment.   Note that the frequency of each microwave channel is exactly 12.6465 GHz higher than the corresponding VHF/UHF channel.

Pickwick, Tennessee, 1982.

A Southern Pine...
...pretending to be a Cable TV Pole.

This tree--a common species of pine indigenous to southern Tennessee--is located in a neighborhood where CATV cables are underground; however, some house drops are overhead.   In this example, the CATV pedestal is located next to one of these pines, and the drop to a nearby house is run overhead, using the tree as a pole.

Poles Supporting T1 Repeaters

A T1 signal (more property a called DS1 a signal) is a 1.544-Mbit/second digital signal.   This signal format was originally designed to carry 24 voice channels over existing twisted-pair copper conductors, although the bandwidth can be (and often is) used for other purposes.

Each T1 circuit requires two transmission paths, one in each direction.   T1 circuits can be implemented over open-wire conductors, twisted-pair copper conductors, coaxial cable, fiber optic cable, microwave links, or satellite links.

T1 circuits, implemented over twisted-pair copper cables, are still in use today to carry voice channels over relatively short distances (up to 20 or 30 miles).   Repeaters (actually, digital regenerators) like this are spaced at 6000-foot intervals, and are usually placed on utility poles or posts.   They are a common sight today along suburban streets and country roads.


West Point, New York, 2001


Brazoria, Texas, 2004

Clute, Texas, 2003

An 1869 telegraph pole (replica).

This pole is a replica of an original telegraph pole, one of hundreds that once stood along the Transcontinental Railroad.

The Transcontinental Railroad was built by two companies, the Union Pacific (building west from Omaha) and the Central Pacific (building east from Sacramento).   The two companies met at Promontory Summit, Utah, north of the Great Salt Lake, in May, 1869.

The site is now known as the Golden Spike National Historic Site, operated by the National Park Service with the assistance of volunteers who act as docents, exhibit-makers, locomotive engineers, and locomotive firemen.

On May 10, 1869, a ceremony marked the completion of the railroad.   Tradition has it that a golden spike was driven into the last tie to mark the occasion.   Actually, there were four spikes, and the "last tie" (a polished laurel beam) was predrilled to accept them.   After the ceremony, the original last tie was placed on display in San Francisco, where it remained until it was destroyed in the 1906 earthquake and fire.   A replica is now on display in the GSNHS visitors center.

The original rails, ties, and telegraph lines were removed in 1942 (steel was needed for the war effort), after the original route was abandoned.   The NPS has reconstructed a mile or so of the line along the original right-of-way, in the vicinity of the visitors center.   As part of this work, several of the original telegraph poles were reconstructed based on historic photographs.

Promontory Summit, Utah, May 9, 1869

Original telegraph poleline
(detail from above photo).
May 9, 1869.

Replica telegraph poleline.
September, 2002.

Jordan, Utah, 2003.

A raptor-nest pole.

This pole supports a nesting platform for raptors (birds of prey: hawks, falcons, eagles, vultures, and owls).   Electric power companies sometimes install platforms similar to this one near their power-handling facilities (transmission lines; substations).   In theory, raptors are attracted to these platforms as potential nesting sites, thereby reducing the possibility that they will attempt to nest on transmission towers or substation equipment.

The Mystery Pole.

This pole supports electric power conductors, telephone conductors, a streetlight, and several pulleys.   What are the pulleys for?

Yerevan, Armenia, 2003.   All photos courtesy of Russell Whitworth, Guildford, UK.


Pole owners are usually pretty laid-back about unauthorized pole attachments as long as they don't get in their way.   But if unauthorized attachments get in the way, pole owners don't hesitate to remove them.   Sometimes gently, sometimes not.