Telephone Power  & CATV Poles

Brooke Clarke 2012 - 2016

Feature Table
Hybrid Fibre-coaxial
Fire & Vegetation


There are different services provides on the utility poles depending on how far from town you're located.  This is a visual guide to what's on them.

Alternating Current Mains Power

At the top is the high voltage AC.  Most of the poles near my house have 12,000 Volts.  At my house it's single phase (2 wires), but closer to town it's 3 phase.  Three phase is required for running motors rated well above 1 horse power, industrial air conditioners, etc.  May be handy for a large home shop if you want to use industrial lathes or other large consumers of power.

Each house has its own transformer that steps down the 12,000 Volts to 220 VAC center tapped.  The center tap has a wire to a ground rod at the base of the pole.  The input to the transformer is fused.  If a short develops between the transformer primary and the secondary the center tap provides a low resistance path to ground thus blowing the fuses on the transformer input.  This is so that a transformer failure will not allow 12 kV AC to enter your house.

My house now has an analog meter, but I've been getting letters for a couple of  years saying they will install a "smart meter" in the near future.

The entry panel to the house has two branches, one fed from each side of the pole transformer (aka: pole pig).  110 VAC circuits are fed between one branch and the center tap (neutral).  220 VAC circuits are fed from both branches.

Closed Circuit Television (Cable TV)

This is a single coaxial cable that has an amplifier at regular intervals to make up for cable loss.  Also there are taps, typically with four outputs to feed houses.  Originally only used as a one way system to distribute analog TV.  Now used with cable modems as a two way internet connection.  The latest wrinkle is to deliver movies as digital data on demand, either free or pay per view.  My house is too far from town so there's no cable TV here.

Fiber Optic Data

This is a way to carry a very large amount of digital data.  There's a FO line that terminates a few miles from my house and from there DSL is routed over the copper twisted pair line.


This is classical analog telephone or more modern Asynchronous Digital Subscriber Line (ADSL) for a two way internet connection.  It uses a much wider bandwidth on the twisted pair copper lines and so can not be used with loading coils that are commonly used to supply analog voice phone service to people far from the central telephone office.  There's distance limit on how far DSL can be delivered.

Feature Table

Fig 1 yes yes

Fig 2 yes yes

Fig 3 yes yes yes Fiber
Fig 4 yes

Fig 5 yes yes
1ph 3wire
Fig 6 yes

Fig 7 yes yes

Fig 8 yes yes yes
Fig 9 yes yes yes BTN-M node
Fig 10 yes

Fig 11 yes yes yes DSLAM
Fig 12 yes

Cap bank
Fig 13 yes yes yes BTN-M node
CATV info
Fig 14 yes yes
my pole
Fig 15 yes yes
my DSL
Fig 16

my DSL
Fig 17 yes yes
my underground
Fig 18
my NID
Fig 19 yes

Fig 20
loading coils
Fig 21 yes

Fig 22 yes

Pwr Two
close up
Fig 23

tel boxes
Fig 24

block inside
Fig 25

pole maint
Fig 26

pole brace
Fig 27

Fig 28

cut pole
new pole
Fig 29

cut pole
new pole


General Instrument, Jerrold Starline BTN-M Broadband Telecommunications Node




Fig 36

Steel Transmission Poles


Click on photo to see larger version.  If your cursor is a plus sign click again for even larger version.
Fig 1
Brooke's Guide to Utility Poles
Single Phase 12kV AC Mains

Copper telephone (DSL) cable.
Fig 2
Brooke's Guide to Utility Poles
Single Phase 12kV AC Mains

Copper telephone (DSL) cable.
Fig 3

Brooke's Guide to Utility Poles
Brooke's Guide to Utility Poles
Brooke's Guide to Utility Poles

Cable TV(fiber only)  top left making a right turn.  Copper pair  telephone cable.  Also see Fig 8

More photos of Cable TV
Fig TV1 Other end of coax after making right turn (marked Cable TV on photo)
Brooke's Guide to Utility Poles

Fig TV2  End of nearby short street
Brooke's Guide to Utility Poles

Fig TV3 pole down Wildwood Dr.
Brooke's Guide to Utility Poles

Fig 4
Brooke's Guide to Utility Poles
Single Phase 12kV AC Mains

A single petticoat insulator corresponds to about 12 kV, see Fig 22.

Two phone trunk cables, one makiing a left turn
and the other going straight.
Fig 5
Brooke's Guide to Utility Poles
The end of the 3-phase 12 kV AC mains. 
There's a water well and storage tank to the right fed by the heavy black cable.

The left-hand drop is a 1-ph 3-wire 120/240V supply and the right-hand one is a 4-wire high-leg delta (Wiki).
(thanks to Paul C. & N. McLain)

There's also a phone feed to the well house.
Brooke's Guide to Utility Poles
Brooke's Guide to Utility Poles
The water tank is located at the peak of the ridge road.  Across the street from the pump house is a residence.

Fig 6
Brooke's Guide to Utility Poles
60 kV Transmission line crosses the road and the 12 kV distribution line.
Fig 7
Brooke's Guide to Utility Poles
3-Phase 12 kV AC Mains with a fuse in each of the three wires.

Copper telephone cable.
Fig 8
Brooke's Guide to Utility Poles
T intersection on the street and on the pole.
3-Phase 12 kV AC going along the main road.
The 3-phase lines to the right are not connected to the main line above because the three switches are open.

This is the idea of a grid.  Lines can be connected together in different ways.  This allows isolating part of the grid while keeping the rest of the grid hot.  Without the switches you would need to shut down a much larger area if there was a problem anywhere.

The Comcast fiber cable makes a right turn here and does not continue on my street.

The telephone cable continues up my street.
Fig 9
Brooke's Guide to Utility Poles
Another T street intersection.
This time all the 3-phase 12 kV lines are connected (switches closed).

220 VAC feed from adjacent pole to a house.

Cable TV coax & BTN-M node

Phone cable and junction boxes.
Fig 10
Brooke's Guide to Utility Poles
3-Phase 12 kV AC near the DSL box.

U-turn is on fiber cable to avoid cutting it.
Fig 11
Brooke's Guide to Utility Poles
Note cross-connect boxes (on right) can appear by themselves,
But DSLAM cabinets (center) will always be accompanied by power cabinets (left).
There's a fiber optic cable from the central telephone office that feeds a box with a DSL converter.
There's also cable TV on the pole.

Digital subscriber line access multiplexer (Wiki: DSLAM)  Note: the maximum distance from the DSLAM to subscriber is about 17,000 feet.
Power box is on left with labels and lights about mains power and generator.
The DSLAM box is in the center. 
Crossover box is the one on the right.

                      Guide to Utility Poles
DLSAM box - DMAX1120 (Google) (top to bottom)
Battery (12 hour)
Primary Shelf
Expansion Shelf
                      Guide to Utility Poles - DSLAM
Crossover box shown below.  Note large punch down areas on left and right.  Each of these is connected to a cable with a large number of pairs.  These connections are not disturbed.  In the center part are the crossover pairs that connect one cable to the other cable.  If a pair has a problem in cable A then that pair can be abandoned and the crossover connected to a good pair.  But when there are no longer any good pairs there's a problem and a new cable needs to be installed.

                      Guide to Utility Poles - Telephone Crossover box

While I was at the DSLAM there were two other subscribers, both of which could receive telephone calls,
but had no dial tone so could not place outgoing calls.

DSLAM box cards at the left with:
2 LEDs are for Plain Old Telephone Service (POTS).
3 LEDs are for ADSL.
4 LEDs are for Optical Cable Transceivers (OC3-XCVR).
8 LEDs are Central Processing Units (CPU).
3 LEDs & 3 Test Points are Power Supply Units (PSU).
4 LEDs & 2 Pair of jacks are ??

When a black cross-connect block is pulled the subscriber is disconnected and a test set can be used to check for dial tone and place a test call.

Backup Generator to maintain DSL during PG&E shutdown.
                      Interlock Kit
DSL is provisioned on top of a normal copper pair phone line.  The phone line falls under FCC Title II regulations, so there's a requirement that it work during emergency situations such as AC power failure.  This is not the case for most other providers of internet service.

Also see Rural Internet, Generators, at&t DSL
Fig 12
Brooke's Guide
                      to Utility Poles
I think this is a capacitor bank used for Power Factor (Wiki) correction.  Many of the loads connected to the AC mains have inductive reactance which increases the current in the transmission lines which is lost power due to heat.  So, by making the load look more like a resistor less power is wasted in heating the transmission line.

In the EU there are rules about the power factor of electrical devices so that the overall system operates near a power factor of 1.0.
Fig 13
                      Guide to Utility Poles

There is a cable TV amplifier that has 2 cables on each end, why?
answer from Neal:
Because cable TV networks utilize two types of distribution cables: -

TRUNK is designed for to carry signals over long distances with minimum noise and distortion. Trunk signal levels are optimized for minimum noise and distortion. Trunks may be cascaded to depths up to 30 amplifiers (although I once heard of a trunk line 67 amplifiers deep). Trunk lines are never tapped. Trunk is typically implemented with 0.750" solid aluminum sheath cable, although other sizes will work just as well. -

FEEDER is designed for short runs within a small area (a block or two) to feed customers. Feeder lines are tapped as needed by neighboring structures, typically one tap per pole. Feeders run at substantially higher levels than trunk in order to provide the necessary level to drive the taps. However, the higher operating levels result in higher distortion levels; consequently, feeders are typically limited to two amplifiers ("line extenders") per run. Feeder is typically implemented with 0.500" solid aluminum sheath cable, although other sizes will work just as well.

The amplifier shown in the photo is a "terminating bridger" (or a "5-amp" in the lingo of line techs, who refer to amps by their Jerrold model numbers). The trunk line enters upper left, and is amplified to a level of around +45 dBmV (which equals about -3.75 dBm, or 177.83 mV RMS at 75 ohms characteristic impedance).

This signal is split three ways, producing three feeder outputs. These are the other three cables connected to the amplifiers. One feeder heads to the left to feed a neighborhood off camera. The other two head to the right to feed two more neighborhoods.

For a detailed explanation, see:
Also on the right there is a tap with a single coax line going to a residence.

A black cylindrical telephone breakout box and a rectangular metal telephone box on the pole.
Fig 14
                      Guide to Utility Poles
This is the pole for my house.
6 kV single phase AC at the top with a transformer feeding center tapped 220 VAC to the house.

The telephone trunk has no tap on this pole, it's on the next pole further from the central office with a a couple of return cables.
This really hurts for DSL since I'm the last house that can get DSL service.
Fig 15
                      Guide to Utility Poles
Close up of my telephone service at the pole.
Fig 16
                      Guide to Utility Poles
This is on the next pole down the street where my two phone cables are branched off the main telephone cable.
You can see the two cables going to the right to my place.
Fig 17
Brooke's Guide
                      to Utility Poles
This is the pole for my house.
The large conduit at the left is the underground 220 VAC  feed to my house.

There are two telephone cables to my house.  The original cable is the one that is buried in the ground.  The small conduit on the right was installed when the house was built to make installing cable TV easier, but there's no way the cable TV company will extend service to those of us who are too far out in the forest so it's being used for a 6-pair phone cable.
Fig 18
                      Guide to Utility Poles
At the upper left of the photo is the electric panel that also has the electric meter.

The box to it's right is the demarcation box (demark) or Network Interface Device (Wiki: NID)

The cable at the bottom center is the original telephone cable.  To it's right is what was supposed to be the cable TV conduit which now has another 6pair telephone cable.  The small conduit to the left is the extension cord for the shipping container.

                      Guide to Utility Poles

This is a 6 line demark box that came with the house.  But the cover was broken.
Note that each of the 6 lines has 2 pair so there's a total of 12 pairs going into the house..

CO Cable Color Code
Home Phone




Fig 23
New 4 line
                      phone demark box
4 phone line box demark

The cable in the large cable TV conduit is a 6 pair CO phone cable.
The other large cable coming up from the concrete is the original CO phone cable and has been cut off, i.e. no longer being used but probably OK.

The medium sized cable coming out of the wall at the lower left is a 6 pair CAT3 cable installed for ISDN service and makes a  home run to the ISDN jack in my office (now used for FAX/DSL).
The upper left wht/org pair is the home phone line.
 The upper right Blue/White pair is the FAX, DSL line. 

Of the group of 4 cables coming out of the wall 3 are quad cables (Red/Green & Yellow/Black) and 1 of them is the ground wire (connects at the top center of the box).

Although this box can support 4 lines there are jumpers so now it's only supporting 2 lines.  I'll change this in the near future when the Panasonic KX-TA824 telephone system is installed.

Fig 24
Inside Jack
                      on Wht/Brn Home Run 6-pair cable
Inside end of ISDN (Wiki) cable, maybe 1999?

Wires have been brought out from the adjacent flush wall jack box and fed to this surface mount RJ-11 Jack.

There are 16 punch down terminals, but they are paired so it's only 8 terminals.

The Red-Green pair to the socket connects to the Wht/Brn pair from the adjacent flush box. They are in the lower left corner.
Not line pair is connected to the Yellow-Black socket wires.
Fig 19
                      Guide to Utility Poles
The left side of the AC mains entrance panel has the underground conduit feeding the analog electric meter.  PG&G says they are going to install a smart meter, but it's been a couple of years and it hasn't happened yet.

The right side contains some breakers.  The door is hinged at the top and will not stay open unless someone holds it.  There's another breaker panel in the garage (see the kitchen oven repair "Wiring for new oven" for a little more on it)
Fig 20
Brooke's Guide
                      to Utility Poles
Small & Large Loading Coils in the cylindrical cases.
These are typically 88 mH Inductors.
Fig 21
                    Voltage Power Tower
This high voltage power tower is visible from my front door.
See close up view (Fig 21) below.
Fig 22
                    Voltage Power Tower
Close up of High Voltage Transmission Tower.  6 Wires or two three phase lines.

Distribution (Wiki) is what's on the wooden poles and is commonly 7.2, 12.47, 25, and 34.5 kV,
"12 kV for the poles on my street.

Transmission (Wiki) is for moving electricity over long distances and is done at voltages much higher than for distribution and the height above ground is also much higher.

You can estimate the line-line voltage by counting the petticoat insulators:
1 - 12 Kv
3 - 34.5kv
4 - 46kv
5 - 69kv
7 - 92kv
22 -345kv

So for this case 5 petticoats = 69 kV line to line voltage or (69 kV/SQRT(3) = 39.8 kV to ground.

PS to take this photo from my front door requires a long telephoto lens ( and scroll down a little).

Fig 25 Pole Maintenance
a. night view
Telephone Pole Maintenance
b. day view
Telephone Pole Maintenance
c. base work
Telephone Pole Maintenance

Man on right (00:00:12) with chain saw or weed eater.
Man on left (00:26:00) working at base of pole.

Osmose - Wood Preservation - Wood Pole Maintenance -

Fig 26 Pole Brace
                      Power Telephone Pole Metal Brace

Fig 27 PG&G Smart Meter Repeater
PG&G Smart Meter Repeater on
                              power pole
PG&G Smart Meter Repeater on
                              power pole

PG&G Smart Meter Repeater on
                              power pole

Over a year ago PG&E installed a smart electric meter but it was read the old fashioned way.
But now Jan 2015, a repeater has been installed on a ridge line up the road and it's now "smart".

Note since this is a PG&E pole they just use the neutral and one of the 115 VAC transformer outputs to power the repeater.

If the power fails at that pole, like happened last week, PG&E can see that the repeater is down since it has an ID. They can also see what houses up stream have power and figure out about where the problem is.

Fig 28 at&t no longer maintaining poles
at&t pole
                      not maintained
PG&E has put in a new pole and moved their wires to the new pole then cut off the top of the old pole leaving the at&t phone cable.  But at&t has not moved the phone cable to the new pole.  It's my understanding that at&t has an obligation to maintain the outside copper wires, but it seems they are not doing it.

These two poles are on my street.  I wonder in how many other places are they ignoring maintenance with the idea that they are going to abandon this outside plant?
California AB 2395 "Telecommunications: replacement of public switched telephone network."
Fig 29 at&t no longer maintaining poles
at&t pole
                      not maintained
PG&E has put in a new pole and moved their wires to the new pole then cut off the top of the old pole leaving the at&t phone cable.  But at&t has not moved the phone cable to the new pole.  It's my understanding that at&t has an obligation to maintain the outside copper wires, but it seems they are not doing it.
Fig 36
                      Transmission Poles 20 June 2019
Steel Transmission Poles 20 June 2019
I'm guessing this is so that in the event of a fire the pole will not burn..
The problem is steel gets weak when heated so may slump, but that better than dropping the line on the ground.
Taken with G6 cell phone from parked car.

See Ukiah 29 June 2019 PG&E Poles -

Hybrid Fibre-coaxial (Wiki)

Instead of the old fashioned cable TV system where only coax was used the system Comcast is using here is called Hybrid Fibre-coaxial.  The frequency compensating line amplifiers have been eliminated by installing nodes every mile or so and running coax to the subscribers where the length of the coax run is short enough that no amplifier is needed.  The system is based on the General Instrument, Jerrold Starline BTN-M Broadband Telecommunications Node.  As far as I can tell this box can use either coax or fiber (Wiki) in the path from/to the headend (Wiki) or downstream.  At the headend (Wiki, CMTS) there are multiple fibers connecting to the internet.  There are up to four coax I/O ports that can go to subscribers.  The classical cable TV system was one way from the headend to the subscriber, but for internet a two way system is needed.

YouTube: Cable Television Node- inside the Fiber - Coax node box
5 - 200 MHz for Return (Up Load) and 50 - 750 MHz for Foreword (Down Load).
If one TV channel takes up 6 MHz then slightly more than 100 channels are available for a single path.  Maybe twice that if a "split" system is used?

DOCSIS 3.0 (Wiki) is the current cable modem standard.  In versions prior to 3.0 only one TV channel was used limiting the bandwidth, but now at least 4 channels are supported with no maximum number defined.  With 4 channels the max download throughput is 152 Mb/s (what Comcast advertises for is small business service).

There is an impact of this wider bandwidth on the Wireless router (Wiki) that you attach to the modem.  The first generation routers
only worked at 2.4 GHz and only supported a limited amount of bandwidth.  The newer routers support multiple channels on both 2.4 and 5.8 Ghz allowing a number of people to have simultaneous connections. 

PS I looked into Mobile broadband modems (Wiki) but they have data caps and only work with a reasonably strong cell phone signal.  Something I do not have.

7039317 Reconfigurable node for a hybrid fiber cable network, Marlin McGregor, General Instrument CorporationMay 2, 2006, - the Starline BTN-M node
Note that two fibers are used in this system.  One for download and one for upload so the system is potentially symmetrical unlike ADSL where the "A" stands for asymmetrical.  This allows for high speed uploads, like needed for video broadcasting (i.e. a Youtube channel).

Fig 31


The input is the upper left fat cable.
There are two outputs the lower left and lower right.

Telephone cable is below the node box.
Fig 32


Can not tell much
Fig 33


One input & 3 outputs one with a tap.

Telephone cable is below the node box.
Fig 34


One input & one output with a tap.

Telephone cable is below the node box.
Fig 35


One Input, 3 outputs one with a tap.

Fire & Vegetation

On 8 October 2017 there was a forest fire very close to my house.  We heard from the sheriff that the probable cause was a tree knocking down a power line.  But today I read an article that said ""The utility company is charged with maintaining its power lines and the vegetation around them to prevent wildfires."  I don't think that sentence applies to trees falling on power lines, but rather to preventing the High Voltage lines (not eht 220 volt lines that feed houses) from touching vegetation.  Note that if the High Voltage lines touch vegetation the electrical arc can state a fire.  So, as far as I know, they maintain a ten foot separation.

I've asked the authors of the article to clarify this.


Cell Phones
FasTrak Vehicle ID Transponder - is an active transponder, not an RF ID tag.
Harris TS1000 ADSL Test Set
Key, Object & Pet Location Tags -
Spying on Cell (Mobil) Phones
Orion Electronics Ltd. Cellular Base Station ST616-CBS
Telephone Tool Kit
Smart Electric Meters
Impedance of transmission lines below their cutoff frequency
Rural Internet (depends on DSL or Cable Modem) - point-to-point WISP service only for those who live on hill tops.
Tempo Sidekick T&N Telephone Line Tester
KS8455L2 Line Loop Tester Telephone Installers & Repairman's Meter
ZM-11 Bridge

N. McLain: OutSide Plant article (pdf), Utility Poles in General (Web page), UPRR abandoned poleline (webpage)


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page created 4 April 2012.