Basic Circuits Theory - Voltage, Short Circuits, Open Circuits

[jkele]

I am new to electronics but i love it, love the idea of building projects and doing cool little things, however that being said i need to get some concepts under my belt first.

Theory Questions

If i have a high voltage wire (say 20 000V) and another wire which is grounded hence is at 0V. If a human being (i am assuming that they are an ideal wire and hence does not induce a voltage drop) was to grab a 20 000V and a ground wire at the same time would they be connecting the 20 000V to a short circuit since ground is at 0V? I have attached an image as it is clearer.

Practical Questions

My biggest problem is looking at a circuit and having an almighty difficult time figuring out what the components are there for. Apart from practice and theoretical development how can i overcome this?

Thanks in advance!

 

[killivolt]

I am new to electronics but i love it, love the idea of building projects and doing cool little things, however that being said i need to get some concepts under my belt first.

Theory Questions

If i have a high voltage wire (say 20 000V) and another wire which is grounded hence is at 0V. If a human being (i am assuming that they are an ideal wire and hence does not induce a voltage drop) was to grab a 20 000V and a ground wire at the same time would they be connecting the 20 000V to a short circuit since ground is at 0V? I have attached an image as it is clearer.

Practical Questions

My biggest problem is looking at a circuit and having an almighty difficult time figuring out what the components are there for. Apart from practice and theoretical development how can i overcome this?

Thanks in advance!

It's Christmas and I'm kinda bored.

Ok, the human body was designed to carry electrical charges: between cells as an example.

20,000 volts of electricity is one thing. It's high enough to potentially be grounded through the human body. However, it's the current needed to drive it through. A typical High Voltage wire in most residential is capable of doing that, have you ever seen a bear blown off a power pole?

Edit: When it comes to circuits I can have the same problem. We have some excellent suggestions for basic Electronics Books. Stick around I think you will learn something that will help you.

Here is something you might be interested in ?

 

[jkele]

Thanks for the answer - that being said it does not address my question completely - like i said however lets forget any real world effects of the human body and think of it just as a ideal wire that we see in circuit diagrams.

So my fundamental question is - is connecting a high voltage wire to ground with an ideal wire in between the same as shorting the 20KV to ground?

P.S : Thanks for the link.

 

[killivolt]

Thanks for the answer - that being said it does not address my question completely - like i said however lets forget any real world effects of the human body and think of it just as a ideal wire that we see in circuit diagrams.

So my fundamental question is - is connecting a high voltage wire to ground with an ideal wire in between the same as shorting the 20KV to ground?

P.S : Thanks for the link.

Yes, it will pass directly through to the ground.

Any Voltage without a load like Motors, Appliances etc. Directly connected to ground is considered a Short to Ground.

Edit: Sorry getting sleepy. Merry Christmas and have fun on ETO

 

[Mikebits]

I am new to electronics but i love it, love the idea of building projects and doing cool little things, however that being said i need to get some concepts under my belt first.

Theory Questions

If i have a high voltage wire (say 20 000V) and another wire which is grounded hence is at 0V. If a human being (i am assuming that they are an ideal wire and hence does not induce a voltage drop) was to grab a 20 000V and a ground wire at the same time would they be connecting the 20 000V to a short circuit since ground is at 0V? I have attached an image as it is clearer.
Thanks in advance!

No, that is incorrect. The human body is far from being an ideal conductor. In fact it is very much like a resistor and as such, it has voltage drop.

What this means? Well, have you ever seen one of those electric hotdog cookers?

**broken link removed**

Get the picture?

 

[jkele]

Is what you are saying - that the hot dog has resistance and hence it builds up heat cooking the hot dog. What parts of my theory are incorrect. In regards to the body acting as a resistor - i did say lets consider it to be ideal for simplicity.

 

[jkele]

Merry Christmas to you too - i shall have fun on ETO.

 

[MikeMl]

As little as a few tens of volts connected head to toe (or arm to arm) can be lethal. Its the current that flows in the vicinity of the heart that stops it. At the heart muscle, it only takes a few mA flowing through it to put it into fibrillation

 

[p.gholap93]

human body is not an ideal conductor to short circuit your 20kV line to ground.It also has finite resistance.
If you directly SHORT your supply(WITHOUT ANY LOAD) line to ground it is considered as short circuit with voltage drop equal to zero an (ideally) and infinte current flowing through it.
Another important concept is power rating(product of voltage and current).When connecting a load across a supply voltage its power rating must be taken into consideration.

 

[killivolt]

No, that is incorrect. The human body is far from being an ideal conductor. In fact it is very much like a resistor and as such, it has voltage drop.

What this means? Well, have you ever seen one of those electric hotdog cookers?

**broken link removed**

Get the picture?

Mmmmmmmm :Wink: Bear Dogs.

 

[Reloadron]

OK, brief off topic:

For those who may remember. I later built one to cook hot dogs.

Ron

 

[killivolt]

OK, brief off topic:

For those who may remember. I later built one to cook hot dogs.

Ron

I can't tell you how much I enjoy the Artwork in that Story. In addition it's in black and white giving it the Dated look and feel. I'm wondering what a copy of that edition would be worth. The information provided is priceless.

This is Great.

Thanks, Ron.

Edit: Check this guy out.

Electric Man

Here's another one.

Serbian Electric Man

 

[jkele]

So what if we have two high voltage wires (20,000V) running parallel to each other and (once again) treat the body as an ideal wire and connect the two 20KV wires do we have a short as there is no voltage drop through the body?

 

[MikeMl]

If the lines are power transmission conductors, and you touch both at same time, there will be a great big flash and bang. Several inches of your hands will instantly turn to steam and vaporize, and you will be dead before you hit the ground.

 

[jkele]

But can that be considered as a short circuit (if we assume that the body is a ideal conductor) then there should be no voltage drop and the short circuit is defined as a thing with no voltage drop (so zero resistance).

 

[#12]

The human body is not an ideal conductor. Even copper wire is not an ideal conductor. However, if you could apply an ideal conductor to short out a pair of 20,000 volt transmission lines, the transmission lines would melt. What sort of project are you working on?

 

[MikeMl]

It is impossible to find an ideal conductor (except maybe using superconductivity near absolute Zero). The human body is actually a conductor with a resistance of a few hundred to few thousand Ohms. Connected across 20KV, the instantaneous power dissipation would be P=E^2/R = 20E3^2/1000 = 400E6/E3 = 400,000W. Can you say flash-bang???

 

[Reloadron]

So what if we have two high voltage wires (20,000V) running parallel to each other and (once again) treat the body as an ideal wire and connect the two 20KV wires do we have a short as there is no voltage drop through the body?

First you really need to define and understand "short" as it pertains to electricity. However, if you want to experience 20 KV in a very current limited mild form just grasp the uncovered top of a spark plug on a lawnmower while holding on to the engine body. That is about 20 KV give or take.

Next if you have two 20 KV lines that are in phase (as in the same 20 KV) and grab them both while you are completely isolated from their ground refrence, then nothing will happen. However, if the two lines have a potential difference of 20 KV between them and unlimited current (for all practical purposes) bad things happen pretty much like Mike put it. Additionally you will really smell bad as well as being charred and cooked dead.

Remember a "short" is no more than a current path of low resistance.

Ron

 

[jkele]

Thanks Ron, why will nothing happen? A short is nothing more that a current path of low resistance, IF WE ASSUME THAT THE BODY ACTS LIKE AN IDEAL CONDUCTOR (i have said this many times but people still talk about the real world effects i want to ignore this just to understand the concepts). What if somebody was to grab them not being isolated from the ground reference?

 

[Reloadron]

Thanks Ron, why will nothing happen? A short is nothing more that a current path of low resistance, IF WE ASSUME THAT THE BODY ACTS LIKE AN IDEAL CONDUCTOR (i have said this many times but people still talk about the real world effects i want to ignore this just to understand the concepts). What if somebody was to grab them not being isolated from the ground reference?

What I said was that if we had two 20 KV lines running in parallel and the AC was in phase nothing would happen as long as you did not provide a path to ground or their point of reference.

I went on to say that if there were two 20 KV lines and the potential difference between them was 20 KV with unlimited current then you become the current path. Mike did the math example based on typical body resistance. Then you would be dead meat.

For anything to happen there needs to be a path for current flow. If I am sitting here totally isolated from ground and decide to shove a paper clip into the hot side of a wall outlet nothing will happen. My body will just be elevated to about 120 VAC and I can sit here and just float at that potential. However, if while hanging on to that paper clip I decide to grasp a grounded water pipe with my other hand I now have a path to ground through me. Not a short but a path to ground. Based on the voltage and my body resistance I will indeed draw enough current to afford a nasty shock. How much current will flow depends entirely on my body resistance which can vary but rest assured with 120 VAC I will know I did something bad!

All we need for current flow is a path (Me) and a high enough voltage to get current flow (120 VAC).

This is a classic UTube video that hits on just "floating". Note the small arc as he gets the helicopter to the same potential as the lines.

Ron