An electric service drop is the main electrical line that runs from the electric company's overhead lines to the service head at your house. Because power company lines are higher than your home, the feeder line that goes to your home literally drops--it descends from a higher spot to a lower spot.
All electricity to your home comes through the service drop. If it goes down, all power in your home will shut off.
You Will Always Have One (Unless Yours Is Buried)
If you have buried power lines in your neighborhood--an increasingly common situation--you will not have this. It only applies to neighborhoods where power is run along poles.
That Pipe Is the Service Head and Mast
Or "weatherhead" or "weathercap." Because the top faces downward, rain cannot enter the conduit that leads down to your service panel. It also acts as a stable, secure point (mast) to tether your service line. In many areas, this tether point must be able to hold at least 200 lbs.
Sections Within the House Are Not Part of the Drop
The service drop does not include the electrical service panel (the circuit breakers. Once you get below the service head. Only the suspended potion is the service drop.
Service Drop Is Installed Before Your Home Is Finished
Temporary service drops can be run to a free-standing pole, a separate building, or even a tree, in some cases.
Drip Loop Defined
That looped wire at the service head is not there because there was extra wire that had to be taken up. Instead, it is an intentional feature called a drip loop.
Water coursing down the service drop line itself will be stopped from entering the house by the drip loop. This is a common feature when electricity and water are together (you are even supposed to create a drip loop when setting up your wet tile saw).
Service Drop Height Requirements
Height requirements are different according to local codes and to the area that is below. In many cases, the drop height above sidewalks must be at least 12 feet high. Above residential driveways, 12.5 feet. And above public roads, the service drops should be at least 18 feet above the asphalt.
In general, drop heights are lower over residential areas due to the shorter objects and equipment typically found there. Large equipment such as "cherry picker" bucket trucks that might interfere with service drops are not usually found on residential property. That is why the height requirement is increased to 18 feet over public roads.
Working on Your Own Service Drop Is Not Recommended
While homeowners definitely can (and are allowed to) do their own electrical work, this is limited to activities such as replacing outlets and lights, running cable, even running new circuits if you feel comfortable. Comfortable or not, working on anything above the service panel should not be attempted by a non-electrician.