Overhead Power Line
The commonest lines you'll come into contact with is 240v single phase can be insulated normally black. Older wire is uninsulated copper cable looks greenish.
Trace the cable back to the main pole you should see between 3 to 5 cables depending on the network and where you are in the country.
These are 415v 3 phase sometimes they have a HV wires above (11,000v) rare but does happen.
These poles are generally BT pole size.
The next size up are 11kV upto 132kV larger wooden poles some areas metal poles / frames.
If you see these you'll likely be in the sticks edge of town etc. They do pass through towns but your gonna have to be stupid to hit one.
The wooden bit someone mentioned is no good, what they are called are paramelli inserts. (Look like wood).
These are used on earthing sets. The sections are glass fibre about 5' / 6' and have this insert near
the bottom they are modular and very heavy def no good for wfp.
That is a brief description of overhead lines.
Above all else play safe don't go near them they may be insulated but you don't know the integrity of the insulation until it's too late.
As for arcing across yes they can but 3' on a LV service is unlikely but not impossible. Pure water should not conduct electricity but would you risk it!
PS Low voltage systems carry a far greater current hence a potential flashover will really do you some harm.
Darren
Ex High Voltage Fitter