Why don't birds get electrocuted on overhead wires

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GeoffreyHansen Minister for Railways

Location: In a FAM sleeper

Just an off-topic question for our electrical experts. I didn't know where else to ask this.

I understand that if I were to touch a railway or tramway overhead wire that I would be electrocuted but birds land on overhead wires all the time but they don't get electricuted. Why is this? Surely the electricity would still be flowing through the wire.

Just curious.

 
newington Chief Commissioner

Location: Getting promoted to Sergeant

Just an off-topic question for our electrical experts. I didn't know where else to ask this.

I understand that if I were to touch a railway or tramway overhead wire that I would be electrocuted but birds land on overhead wires all the time but they don't get electricuted. Why is this? Surely the electricity would still be flowing through the wire.

Just curious.

- GeoffreyHansen

I'm no sparkie, but a WSITD tells me that you have to have a full circuit for electricity to flow. Thus, for you, or a bird, to get zapped, you need to create a full circuit, which in most electrocution cases, is touching the ground as well. With birds, you occasionally see dead birds in the gutter, because they touched two wires at once, thus creating a full circuit, from one wire to another, with the bird being part of the circuit.

again, just a game stab.

 
Veyron407 Junior Train Controller

An explanation:

If I touched an electrical wire while standing on a ladder, I would be electrocuted, as I would be relative to the ground.

If I were falling from the sky and landed on electric wires, I would not be electocuted, as I would not be relative to the ground. Same with birds.

 
Jajb94 Deputy Commissioner

Location: In a BAM

It is because they are only touching one wire,

In a house (Im using this setting so it is easy to explain) the power points have 3 holes, 1 (which is the top left of the female socket) is the live wire, the right of the same socket is the neutral socket and the bottom centre is of course the earth, If the live wire is not connected to either the earth or the neutral wire, no current will flow. so, if one of those birds was to somehow touch 2 wires at the same time, there would be a difference in voltage, I.E 1 could be at 240V and the other at 0V there is a difference of 240V which would conduct the electricity from one to another through the bird with potentially fatal consequences

Having said all that, if you are touching anything other than the wire, the ground perhaps or a non insulated ladder you would be part of the shortest circuit to an area of different electrical potential (somewhere the electricity would discharge)

Although, if you touched 2 wires that were at the same potential - basically the same wire that was connected at both ends but separated, theoretical you shouldn't get electrocuted, but dont try it at home

 
Grantham Minister for Railways

Location: I'm with stupid!

Birds don't know enough about electricity to get electrofried.  Wink

 
Pressman Minister for Railways

Location: Wherever the Tin Chook or Qantas takes me

Birds don't know enough about electricity to get electrofried.  Wink

- Grantham


ewes gotta touch two wires (as said above)

 
lsrailfan Chief Commissioner

Location: Somewhere your not

+ you don't see birds spread-eagle over 2 wires.....

 
Pressman Minister for Railways

Location: Wherever the Tin Chook or Qantas takes me

+ you don't see birds spread-eagle over 2 wires.....

- lsrailfan

That would depend on the size of the eagle  Razz

Sowwwy ..... couldn't resist it!  LaughingLaughing

 
MBAX Chief Commissioner

Location: Mostly the Imperial

+ you don't see birds spread-eagle

- lsrailfan

Not even in the mags that you read... Question

 
lsrailfan Chief Commissioner

Location: Somewhere your not

Shhh Roy- Youll reveal my secret  Mr. Green

 
msilsby Assistant Commissioner

Location: Melbourne, Victoria

You're reading the wrong mags.

Hmm. 'Reading' might be a loose term . . .

(training material thanks!)

 
Gwiwer Rt Hon Gentleman and Ghost of Oliver Bulleid

Location: Loitering in darkest Somewhere

The explanations given above are fundamentally correct.  In order to suffer electrocution one needs to be a part of the circuit from supply to earth.

Birds (and other creatures) which settle or perch on a single line or live rail do not complete a circuit and thus there is no electrical potential through their bodies.  They feel nothing and suffer no effects.  

If, however, they accidentally fly between two live wires and contact both they usually suffer instantaneous death by electrocution and the resulting short can cause a loss of power to customers.

 
Pressman Minister for Railways

Location: Wherever the Tin Chook or Qantas takes me

It should be noted that with high voltage lines, you don't have to actually touch the two points, the air around the cable is electrified, (the distance depends on the voltage level).

 
HMC1989 Chief Commissioner

Location: Behind a desk.

Slightly off topic but how's this for a job.


http://www.youtube.com/watch?v=7nX3SxRrqWA&feature=related

Hope they get paid well.

 
Pressman Minister for Railways

Location: Wherever the Tin Chook or Qantas takes me

Live line maintenance is common place here in Oz!

 
Expost Deputy Commissioner



I tried to pick a photo that showed clearly the set up in Qld. This happens to be the end of the wire at an overhead coal loadout, but will give you the general idea.

The steel overhead structure, and all the masts off into the distance, are not electrified, as they are directly mounted to the ground. But note the insulators, 2 vertical and 2 at an angle, supporting the end of the overhead wiring. Everything that is supported by these insulators is live. (Note the wire at the top of the masts on the left is not live, its an earth return, hence no insulators)



Now, note in this pic, the insulators on the supports of the overhead wires. Because they are insulated from the masts, the supports are also live, along with the wires. Note also, most of the wires at the tops of the masts are also insulated, they are live as well.

If a bird lands on the wire or supports, and stretches its wings enough to contact the mast, BOOM, fried bird. If it doesnt come into contact with the mast, then there is no problem.

Thats an issue with kids climbing masts, they dont realise the supporting structure is live. If they climb the mast, and reach out past the insulator to grab the angled support, then they are not happy chappies, unfortunately. Thats what the signs are for, I just wish people would read and understand them.

Cheers

Expost

 
Gwiwer Rt Hon Gentleman and Ghost of Oliver Bulleid

Location: Loitering in darkest Somewhere

Thats what the signs are for

- A user

And the fences.  Where they exist.  I suspect few countries have as much electrified line without fences as Australia.  In many countries you will find substantial fencing alongside electrified railways.  It still doesn't keep everyone out.

Pressman's point about the eletrostatic field around (particularly) high-voltage transmission lines is well made.  With a family member who worked for a time as a live lineman I have some understanding of the nature of this particular beast and of the risks involved.

Though while the risk is real and can be lethal most high-power lines transmit AC current which tends to knock you away with a stable arc rather than DC which tends to attract you to it in an unstable arc.

That's getting a bit technical for birds on wires but the point has been well made.

 
newington Chief Commissioner

Location: Getting promoted to Sergeant

Thats what the signs are for

- A user

And the fences.  Where they exist.  I suspect few countries have as much electrified line without fences as Australia.  In many countries you will find substantial fencing alongside electrified railways.  It still doesn't keep everyone out.

.

- Gwiwer

There are many places near the extremities of the electrifried (sorry couldn't resist) that are not fenced, interestingly.

 
BrianB Chief Train Controller

Location: Brisbane

Slightly off topic but how's this for a job.


http://www.youtube.com/watch?v=7nX3SxRrqWA&feature=related

Hope they get paid well.

- HMC1989

Brisbane's Aeropower is one of the world's leading specialists in this field.

http://www.aeropower.com.au/electrical/index.htm

In the left hand menus, click on Video, and have a look.

I'm retired now, but when I was a computer consultant, some 15 odd years ago I trained the Aeropower engineers in the use of Microsoft Project, to help them plan their daily operations, in their head office at Strathpine.

Athough the helicopters are based at Redcliffe aerodrome, there is a little patch beside the head office building, tucked in between the building and a big high-voltage substation next door - to watch the expertise of the pilots coming in to pick up items from head office, is a marvelous thing to watch as they are only about 10m from very high voltages.

 
JGS - Moderator Chief Commissioner

Location: Junee NSW

+ you don't see birds spread-eagle

- lsrailfan

Not even in the mags that you read... Question

- MBAX

Well, there goes coffee out of my nostrils and all over the monitor!

Cheers,

Matt

 
Aaron Minister for Railways

Location: University of Adelaide SA

Live line maintenance is common place here in Oz!

- Pressman

Not to mention just about the World over! I'd wager that the vast majority (probably 75+%) of the World's electrical maintainence is done live, because the rest of the pesky customers hate blackouts killing their TV, computers and internets etc.

 
Aaron Minister for Railways

Location: University of Adelaide SA

It should be noted that with high voltage lines, you don't have to actually touch the two points, the air around the cable is electrified, (the distance depends on the voltage level).

- Pressman

Just for interest, that distance for the very EHT wiring exiting sub stations and power plants heading cross country is of the order of about 4.25m, much beyond that and you're going to feel some pain or get dead!

 
GrahamH Chief Commissioner

Location: At a terminal on the www.

Actually the bird should get a very tiny current through it. The current will divide inversely proportionally between the low resistance of the length of wire between the bird's feet and the higher resistance through the bird.

 
574M - Moderator White Guru

Location: Shepparton

Is that why I see so many one legged birds near railway liines? The panto shears off their claws... ?

 
Speed Minister for Railways

The wires should start shaking as a train approaches. With no wind and nothing else shaking, I'd hope that this would be enough to make a bird fly elsewhere.

 

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