Commonly called "telephone poles," utility poles carry a lot more than just phone service.
They also conduct electrical power, street lights, internet, cable TV, signs, surveillance cameras, traffic signals, pedestrian signals, and seasonal decorations.
|Anatomy of a Utility Pole|
Things to Look for:
• Functions are stratified by height, like life in a rain forest. Electric power at the highest voltage is carried on the top. In the USA, there are typically three uninsulated aluminum wires (each about 1/2 inch thick) spaced across the top crossbar, held up with three insulators.
• For every few houses or businesses, there's a set of transformers—three big cylinders. These lower the voltage from the Primary Distribution Zone to the Secondary Distribution Zone below. Inside the transformer typically there's a coil of copper wire wrapped around a steel core, all bathed in oil. These generally don't explode in storms; there's a cigar-sized fuse that's designed to blow.
• Secondary distribution lines are also in threes just below the transformer level. The primary and secondary zones together comprise the "supply space."
• Street lights, yard lights, and traffic signals are wired to the Secondary Zone. Sodium vapor street lights are rapidly being replaced by LED lights, changing the color of the urban night from yellow to cool white.
• The twisted wires running off to buildings from below the transformers carry electrical power. Commercial businesses with high energy demands require thicker bundles.
• The Communications Zone is the bottom level. It includes both fiber optic and coaxial cables with junction boxes and repeaters. These are usually the thickest cables. They serve internet, cable TV, police and fire alarm systems, and telephone.
• There's normally more space between the Secondary and Communication zones than there is in the pole I drew at the top of this post. This space is called the the "Safety Zone," and its purpose is to protect telecom workers from high voltages.
• Telephone cables often can't support their own weight, so they hang from, or are lashed to, a thinner, uninsulated support strand, and they droop below that strand for stretches. There are various methods (such as loops) used to relieve stress or to store excess cable. Fiber optic cables sometimes have U-turns to store a longer section of cable without cutting it or breaking it.
• Horizontal rectangular boxes are junction boxes or splice boxes, giving access to the telephone connections. They also hang from the support strand.
• You'll see thin wires connecting to buildings for the phone service from this level.
• The public or yard sale area is at the bottom. It includes posters and notices that people post on the pole. There are also numbers near the base that identify the pole.
• Poles are black at the bottom from creosote (or a modern substitute) to protect the pole from rotting.
• Support cables run down on a diagonal and attach to a stake in the ground. Draw these lines straight because they are under tension. They keep poles upright by opposing lateral forces. Those lateral forces may come from 1) Turns in the road, 2) Systems of heavy cables branching off to the side, or 3) Dead ends.
• All hanging wires follow a catenary curve between the points of support. These can generally be best drawn with the artwork turned upside down.
If there are utility service professionals reading this post who can help me correct any errors, please let me know in the comments.
A highly visual book that I recommend: