Explain why a bird sitting on a 400 kV power transmission cable is not electrocuted.?

Answer 1

Because there is no route to Earth.

Answer 2

Electrocution ocurs when a sizeable current passes from a part you touch that has a high voltage on it through your body to a part of your body that touches the earth. If you had one hand on that wire and another on the metal tower you would be toast. If you were in an insulated bucket and touched just the wire without a ground path you would not get electrocuted (do not try this at home).

The same thing happens with a bird. It flies though the air and lands on the wire without touching a ground path so it has no problem. Sometimes squirrels try the same thing by leaping but end up touching both a live wire and a grounded part and that is one less rodent on the earth.

Answer 3

The Electrical Eng with 40 yr experience was basically right;

Look at it this way - Voltage is the force driving electricity. If you have a 400kV transmission line, this means it has 400kV between phases and about 230kV between a live cable and earth.
The birds feet are a couple of inches apart on the same wire - and it is touching nothing else. The voltage difference between its left foot and right foot will be tiny. Very tiny - a decimal point with lots of zeros after it.
Current is equal to Voltage divided by resistance.
I have no idea what the resistance of the average bird is - lets say (for the sake of argument) 100 ohms.
For the sake of argument - we'll say the voltage across the bird (from left to right foot) is 0.000001 volts (In reality it'll probably be smaller than this).
Hence the current passing through the bird is 0.00000001 amps. It's not going to notice.

Does anyone know a ball park figure for the resistance of the average crow?

However - Birds don't ever actually sit on 400kV lines. This is because when landing on a line they do become charged as a result of the frequency and the changing e.m.f. At voltages above about 100kV - this is uncomfortable for the bird.

Answer 4

electrical force will always take the easiest route down the best conductor. The cables in the wires are excellent conductors and so there is absolutely no reason for the current to touch the bird. If the bird short-circuited the current by making a lnk with either the ground or another cable then the electricity will temporarily divert through the bird to ground or the other wire and it will be burnt to a crisp

Answer 5

David C remarked about the bird being uncomfortable on a "400Kv" line.
That is the closest of the dozens of answers, so far.

The statement made about "step potential" - has no bearing on this bird. The bird sitting on a wire could not be near the size needed, to have its feet apart enough to realize enough voltage difference between its feet to feel it.

The "step potential" phenomenon is much more suited to a voltage difference on a area of land that a high tension line that could somehow be still live but discharging into ground and if you were to take large steps away from the higher charged area, and considering the voltage drop per foot of your average dirt, going away from the charged area - you would realize a larger voltage potential from one shoe to the other as you traveled. Short walking steps are a way to reduce this.

In over 45 years - I have only seen one stupid pigeon sitting on a high tension line.

BIRDS DO NOT SIT ON HIGH TENSION LINES, other than that exception I witnessed.

I welcome anyone to see birds on any wire of more than 34.5 KV, sub to sub distribution lines. Even that voltage turns them away normally.

Birds and other living things have what is called " body capacity".
The bird in question will have a minimal, to zero, inherent charge.
When birds approach high tension lines - they feel the intense electrical field around the HV lines and they veer away. The HV lines would actually 'fuzz' or begin to arc towards the approaching bird, because of the mass of the bird.
You won't see birds on these HV lines.
They will sit on the top grounded conductor - some towers have 2 of these top grounded conductors, and birds will happily sit there.

Take a 8 hour shift with an easy chair and watch a line, again no birds on the HV.

Local distribution of perhaps 13.8 Kv or lower - birds will approach and sit. The electric field is much less intense.
But it is correct by mention of some answers here, about any contact of an animal - phase to phase, or phase to ground, that will cook the visitor.
These phases being lower voltage are much closer to each other and closer to the support pole or tower via shorter insulators because of lower voltage. Therefore better chance of a arc or flash over through the animal.
I was at a local festival when a wayward squirrel had arrived to the top of a pole transformer can, turned the right way, contacted 7200 volts and made a good flash bang and hit the ground with a thud, charcoal now.

Answer 6

You already have the answer (no idea why so many people answer something already answered with the same answer) but you may also be interested to know that high voltage maintenance crews are sometimes lifted in trolleys by helicopter to travel the length of the lines doing inspections and maintenance. They don't get shocked for the same reason although there is a careful procedure making the first connection as current will flow to charge up the trolley. The bird is small and so doesn't have to worry about charge current because it is also small

Answer 7

Animals are damaged by electricity only when it flows through them. A bird sitting on a power line is surrounded by air, which is a good insulator. No current flows through the bird, and there is no harm done. For the same reason, maintenance workers can sit on live transmission lines as long as they get there using insulated ladders and ropes, and keep a good air gap between themselves and the tower steel.

Answer 8

In order to be electocuted, you must have a completed circuit, i.e. be earthed. Because the bird is purely sitting on the cable (nor did it touch anything else when it landed on the cable), it is not earthed, therefore the circuit is not complete, and the bird is not fried.

Answer 9

Because it isn't earthed, the electricity has nowhere to travel to, therefore the bird is live but would only be electrocuted if the current could flow through.

Answer 10

Electricity will always flow to earth through least resistant path. In this case the bird does not provide a path to earth so can’t be electrocuted.

Answer 11

ALL OF THESE ANSWERS ARE WRONG! WRONG! WRONG......

A bird standing on live wire with its feet apart has a higher restistance through its body than the wire between its feet.
Therefore there is no current flow through the body of the bird.
It is the same thing as a person hanging on a live wire in space there is a greater resistance between the hands than the wire between the hands, hence NO CURRENT FLOW AND NIL or an extremely small difference of potential.
This is called "Step Potential"

Electrical Engineer (ret.) with 40+ yrs experience