The Carlisle Mosquito Online

Friday, August 1, 2008


What’s up on Carlisle’s utility poles?

The town of Carlisle has a necklace of wires and cables running overhead, all carried by hundreds of poles. Many poles hold odd-looking equipment such as transformers, junction boxes, remote circuit switches, telecommunication equipment, and lots of Hendrix hanging brackets.

A pole near the library holds a vacuum fault interrupter (rectangular box near top) that works in conjunction with the antenna on top and smaller remote switching station box below to enable remote monitoring of the power lines.

Hierarchy of wires

To understand what is on the poles, one first needs to know where certain items must be placed. Space on utility poles must be shared by power companies, telecommunications and municipal emergency services, according to the federal “Joint Attachment Law.” The top of the pole, the “supply zone,” is reserved for insulated high-voltage wires and related equipment such as transformers, used to “step down” the voltage. Generally, in Carlisle, there are three high-voltage wires, each carried on an insulator, with one thinner ground wire along side. Infrequently, below the high voltage wires there may be a run of lower-voltage power lines. Often there are lightning arresters, used to stop the surge in power in the case of a lightning strike. High-voltage insulators, first made of green or blue glass, were later replaced by ceramic material and recently, by a type of plastic.

Shared space

The next lower level, which must be at least 30 inches below the high-voltage wires, is reserved for telephone and telecommunication cables and equipment. The empty space between the zones is called the “communication safety zone” to allow anyone working below to have head clearance so they do not accidentally come in contact with live electrical wires. (The electrical workers can protect themselves by using circuit breakers.)

Below the safety zone are coaxial cables, junction boxes, amplifiers, and tension brackets (which look like snowshoes), used to allow aluminum coaxial cable to expand and shrink with extreme cold and heat. Below the cable area is the space for telephone and fiber optics. There can be two or more cables, telecommunication boxes, T1 signal repeaters (see photo at right),

One pole serves many purposes. Note the daylight sensor located on top of the streetlight.

and more junction boxes. The bottom level on a utility pole is for municipal fire and alarm wires. A public utility meter may be installed at this level. Below this level the ground wire, if any, flows into the ground. It should not be spliced or left hanging loose.

Emergency shutoff

The poles in Carlisle are owned by both Verizon and NSTAR, both of which contact the town when there is a problem, or when major maintenance is planned. If necessary, power to the whole town can be cut, said Fire Chief David Flannery. “In an emergency we have special telephone numbers we can call where the emergency call center can actually shut the power off to the entire town with the push of a button.” Though this has not happened since he has been a firefighter he retold an incident in which the emergency workers need to shut off the power. “I do remember when I was very young, perhaps 13 or 14, and working at the school one summer a Boston Edison worker working on the switch in front of the Gleason Library was electrocuted up at the top of the pole. The Fire Department responded but couldn’t reach him as it was too far for the ladder on the fire truck. We waited for another truck with a bucket to come up from Bedford and they got him down. They did CPR and the ambulance came from the Concord Fire Department. We didn’t have an ambulance then. It was a scene that was horrifying for all that day.”


Ever notice short poles or pole fragments with only one or two wires left near a new pole? There can be a delay between installing a new pole and removing the old one, because only

Cable and phone service boxes on pole with support pole.
Another cable service box.
A pole fragment hangs with cable attached.
A T1 signal repeater, also called a digital regenerator, carries voice signals short distances up to about 20 miles. It may be placed at the entrance to a new development, whose cables are run underground.

the companies’ authorized personnel can transfer the lines for each utility (energy, cable, telephone, etc.) After the last line is moved (a process that may take months) the official “mover of poles” (Verizon or NSTAR) returns to take the last bit of pole away. Poles are subjected to inspections, but it is unclear how often.

Some poles have a half pole, or “push pole” leaning against them, as if the taller pole were about to fall over. Utility poles that are installed on corners or are at the end of a line can be subject to sideways pressure. The push pole supports the main pole, and is in place of a long “guy wire.” In some cases an additional pole is installed across a road, with a guy wire running from the utility pole to the support pole and then to the ground. This is done when there is not enough room for supports, for instance by a sidewalk.

From tree to pole

Carlisle’s hundreds of utility poles look similar but have very different origins that reflect the changing methods in wood utilization. The most common source for utility poles is Southern Yellow Pine and Douglas Fir. Chestnut trees, naturally resistant to rot, were used early on but the blight in the 1920s drastically reduced the supply. Cedar, with creosote painted on the bottom, was used for a short time, but was found to have a lifespan of just twenty years. To learn more about a specific pole look for the burnt-in code that gives interesting information such as the type of wood, the year of treatment, and the type of preservative. Some common timber codes:

WC = western red cedar

WP = ponderosa pine

JP = jack pine

LP = lodgepole pine

NP = red (Norway) pine

DF = douglas fir

SP = southern pine

WL = western larch

Very old poles may have “date nails,” which were first made from copper. These nails have the year of installation and, if older than 1940, the length of the pole. Use of the nails was discontinued by the 1950s in most areas.


Carlisle’s poles were treated with three preservatives: creosote, pentachlorophenol and inorganic arsenic compounds. Creosote is a dark, oily liquid that noticably darkens the poles. Creosote went out of favor in the late 1970s, but there has been a revival in the use of

A hendrix hanging bracket.
An amplifier attached to cable/broadband cables contains modules to boost signals. Feeder wires lead from the amplifier to individual houses.

creosote recently, because it is considered less toxic than some other preservatives. Pentachlorophenol (on orange poles), is a synthetic material that was used in the 1970s and 1980s. Inorganic arsenic compounds are created when elemental arsenic combines with oxygen, chlorine, or sulfur. They give a green tint to poles. Inorganic arsenic has been used since the late 1980s. Poles can last well over 30 years. When removed, they are considered hazardous waste due to the preservatives. More information about creosote is available at:, about pentachlorophenol at:, and more about inorganic arsenic at:

Most of the time people drive by utility poles without even noticing they are there, but Carlisle’s collection of poles have lots of interesting gadgets on them, some old, some updated. Take a look the next time you take a walk around your neighborhood.


Did you know?

• The first United States poles were installed in 1844 for the telegraph lines.

• Carlisle’s electricity began arriving in 1911 but it took until 1930 to install enough poles for all residents.

• Swimming pools should not be installed under utility wires.

• When a house is being moved, NSTAR is required to shift the wires out of the way at no cost. But if poles are to be moved the customer pays.

• Power companies and cable companies by law pay a local tax for each pole they use, but telephone companies have been exempt until this spring. Verizon is appealing the new tax. ∆

© 2008 The Carlisle Mosquito