If say a pylon wire were dangling low because it was broken, at say 240,000 volts, would my body not need to complete the circuit for the electricity to flow? i.e. the electricity would need to flow back to its source (the grid/power station).
Surely it could be touched and nothing would happen? I understand that if you were standing on a piece of metal that then was connected to the base of the pylon, it’d flow, but say I was in a big field on dry grass?
Comments
If you’re standing on Earth, your body completes the circuit to ground. This is why birds can sit on power lines and not get killed.
At 240kv what you’re standing on doesn’t matter. If you are within a couple feet or so of anything that can provide a return path (like the ground) you will be a crispy critter. And the current will arc to you before your fingers actually touch the conductor.
The breakdown voltage – the voltage at which something that doesn’t ordinarily conduct, starts to conduct – of dry skin is about 35 volts, for comparison.
Voltage, like your 240,000 volts, is measured between two points. When not stated, the other point is usually earth ground. So voltage is the potential between that wire and the ground. Current will happily flow through anything that completes that circuit, like your body.
Another way to think about it is: Why are the wires placed up on pylons in the first place? It’s to keep them from coming in contact with the ground, or anything electrically connected to the ground, like trees, buildings, people, animals, etc.
Also, at higher voltages, dry grass would be a very poor insulator and not protect you at all.
Not quite how that works. Because the EARTH can “complete the circuit” by basically being a giant sponge that will absorb a ton of electrons.
So while sure the electrons in the power line would like to go back to the source and complete the circuit, they’d also LOVE to discharge into the ground too, and at that many volts your body is a good enough conductor to zap through.
You are correct about electricity wanting to get back to source, but in commercial power systems one side of the source is connected to ground, the Earth. This makes the Earth part of the circuit.
If you are standing on the Earth and touch a line then you complete the circuit through the Earth.
You specifically mentioned dry grass. Yes, dry grass is a better insulator than metal or salt water and many other things. But at 240,000 volts the insulation begins to not insulate very well. It’s called “breakdown voltage”, and it occurs when the voltage gets high enough that the insulation can no longer withstand the pressure and begins to “leak” current through the insulation. All insulators have a breakdown voltage, but some are higher than others.
Current is the flow of electrons through the material. Conductors are materials that have electrons that are loosely bound to the atoms and are easily pushed by the voltage through the material. Insulators are materials that have electrons that are tightly bound to the atoms and are not easily pushed by the voltage through the material. But if enough voltage is applied the electrons of any material will eventually begin to move. Once a few start moving it causes a cascade effect, somewhat like the dam of a lake failing, and the material then goes into the breakdown condition where a lot of electrons start to move.
Technically you’re right, your body wouldn’t be completing the original circuit. Your body is completing a whole new circuit.
Your body conducts electricity, and the ground can absorb nearly unlimited electricity. This is a complete circuit.
At two hundred volts, you have to complete the circuit. At two hundred thousand volts, just about anything can complete the circuit. Air, dry grass, wood, it’ll become conductive under high enough voltage.
“The power company essentially uses the earth as one of the wires in the power system. The earth is a pretty good conductor and it is huge, so it makes a good return path for electrons.”