What's in those gray or green utility boxes that are everywhere?

Question

You've seen them they're on cement pads usually... maybe 5 feet by 3 feet by 5 feet tall.... around here they're gray or green. What's in them?

Answer 1

If they're humming or have radiators/fins out the back, those are most likely padmounted compartmental transformers. Inside them is high voltage (typically 12,000 volts or more) being stepped down to 120/240 for your home, or slightly different voltages for commercial and industrial customers. (typically 120/208 and 277/480) Transformers come in many different sizes, depending on the ratings of the device.

Transformers generally have only 1 or 2 doors, and the doors are on one side of the box.

Other green boxes about 5' x 5' x 3' high are pad-mounted switchgear. These contain high voltage switches and fuses used to operate the underground cables. Switchgear can have multiple doors, usually on opposite sides. The link below shows photos of switchgear from one of the manufacturers.

Answer 2

Sounds like you are talking about transformers.
They change (i.e. transform!) the voltage of the electricity on the overhead pole lines (or underground lines) to a lower voltage that can be used in homes and businesses.
The reason that they are so tricky to distinguish is that (for safety and security reasons) any parts that can be damaged or cause damage are covered up. If you look closely, you should see a door with a lock and/or a 5-sided bolt holding it shut.