How does circuit complete through ground(earth)?

Status
Not open for further replies.
R

roy167

Member
Location
geneva
We have heard about how an earth is a one large sink conductor whose potential doesn't change no matter how much current is sink into it. Let's say I have a small single phase transformer, the secondary of transformer neutral is grounded and I hook up a bulb 100 meters out. I'm only running 2 wires from line and N from transformer to a bulb. I go touch the hot lead at the bulb, will I get shock or not? Note in above example, I haven't run any ground wire or there is no bonding.

We know in order to get shock, there has to be return path to source though person's body.

If I get a shock, that means the current must flow through the ground to it's source(transformer neutral terminal which is also grounded)
 
roy167 said:
We have heard about how an earth is a one large sink conductor whose potential doesn't change no matter how much current is sink into it. Let's say I have a small single phase transformer, the secondary of transformer neutral is grounded and I hook up a bulb 100 meters out. I'm only running 2 wires from line and N from transformer to a bulb. I go touch the hot lead at the bulb, will I get shock or not? Note in above example, I haven't run any ground wire or there is no bonding.

We know in order to get shock, there has to be return path to source though person's body.

If I get a shock, that means the current must flow through the ground to it's source(transformer neutral terminal which is also grounded)
Click to expand...

You have realized a very important thing, namely that the return current of a circuit needs to go not to ground but to the opposite pole of the current source.

In the situation you describe there would be no shock (except for a possible small current resulting from the capacitance between the source and wiring of the circuit to earth.

It is often more useful to think of the earth not as a current sink of infinite capacity but as a conductor of zero ohms resistance. (There will be resistance in the circuit though because each electrode (including your foot) will have an often large resistance with respect to remote earth (a hypothetical electrode connected to earth a great distance from your electrode being tested), the point where you are measuring earth voltage.
 
I'll add a couple notes here.
  • You said the transformer neutral is grounded. Earth (to some degree) provides a return path other than the neutral conductor.
  • Your body must be grounded (to some degree) to complete the circuit using earth or the local equipment grounding as the return.
If the system was not grounded, there's a good chance you wouldn't get shocked.
 
GoldDigger said:
It is often more useful to think of the earth not as a current sink of infinite capacity but as a conductor of zero ohms resistance. (There will be resistance in the circuit though because each electrode (including your foot) will have an often large resistance with respect to remote earth (a hypothetical electrode connected to earth a great distance from your electrode being tested), the point where you are measuring earth voltage.
Click to expand...

So the current shall flow in accordance with voltage divided by sum of resistance between you and ground + ground resistance( 0 ohms) + ground rod resistance on the transformer end. Is this correct?

If yes, the ground is acting as a conductor?? isn't it? otherwise there is no way to get back to the source.

The current may not flow because of the potential difference, as the post above says. However, we know, any time there is a potential difference the current does flow. So there is a lot of contradiction in what we are saying.

I know bonding provides low impedance effective return path so OC devices can open. I'm interested in knowing, is earth the conductor of electricity? can it be considered as one large conductor of zero ohms? All the other nuances such as resistance between your feet and ground, ground rod resistance, capacitance etc etc is in its place.
You have realized a very important thing, namely that the return current of a circuit needs to go not to ground but to the opposite pole of the current source.
Click to expand...

You need effective return path for fast opening of over current devices. To get a shock, you only need less than 100 milliamps. In my above query what I'm interested in knowing is, will there be any tiny amount of current? or it will be open circuit meaning no current, not even 50 milliamps.
 
Last edited:
roy167 said:
.... the secondary of transformer neutral is grounded and I hook up a bulb 100 meters out. I'm only running 2 wires from line and N from transformer to a bulb. I go touch the hot lead at the bulb, will I get shock or not? Note in above example, I haven't run any ground wire or there is no bonding.

We know in order to get shock, there has to be return path to source though person's body.

If I get a shock, that means the current must flow through the ground to it's source(transformer neutral terminal which is also grounded)
Click to expand...

You are being a little confusing here. Is the transformer secondary grounded or not? You say it is grounded but also say there is no bonding. Bonding and grounding are different but related terms....

If the neutral of the transformer is grounded, then you will likely get some sort of shock. The current path is from transformer to hot through the body then through the earth to the grounding electrode and to the other transformer terminal.

If the transformer is not grounded, then there is no current path (except for capacitive coupling as already noted) and thus little to no current flow and little to no shock.

-Jon
 
roy167 said:
We have heard about how an earth is a one large sink conductor whose potential doesn't change no matter how much current is sink into it. Let's say I have a small single phase transformer, the secondary of transformer neutral is grounded and I hook up a bulb 100 meters out. I'm only running 2 wires from line and N from transformer to a bulb. I go touch the hot lead at the bulb, will I get shock or not? Note in above example, I haven't run any ground wire or there is no bonding.

We know in order to get shock, there has to be return path to source though person's body.

If I get a shock, that means the current must flow through the ground to it's source(transformer neutral terminal which is also grounded)
Click to expand...

There is potential from all ungrounded conductors of the secondary to earth because you did ground the neutral conductor.

Keep in mind you may not have all that good of a connection to earth yourself and that may limit the amount of voltage across you body to only a few volts instead of a full 120 volts, lessening how severe the shock may be. Good clean dry footwear may insulate you well enough you don't get shocked at all. Take your shoes off and stand barefoot on well saturated soil then touch the ungrounded conductor and you get a much more severe effect.
 
roy167 said:
I'm interested in knowing, is earth the conductor of electricity? can it be considered as one large conductor of zero ohms? All the other nuances such as resistance between your feet and ground, ground rod resistance, capacitance etc etc is in its place.
Click to expand...

Earth is a conductor. It is not a very good conductor compared to say copper, but there is so darn much of it.

For 60 Hz current and electrodes spaced far enough apart, you can _approximate_ the Earth as being a perfect conductor, and consider all of the resistance as being concentrated at your grounding electrodes or contact points. An approximation is _not_ exactly correct; it is a simplification which is close enough for many applications.

-Jon
 
You are being a little confusing here. Is the transformer secondary grounded or not? You say it is grounded but also say there is no bonding. Bonding and grounding are different but related terms....
Click to expand...

Yes, on purpose we are not bonding the transformer and or bulb enclosure etc, no bonding wire is run, just 2 wire. Only transformer neutral is connected to the ground rod. Transformer chasis is not connected to neutral and or ground rod.

Now In an another example, I was going to ask, let's say we do not ground the transformer secondary, Will the person get shock? If he does, it has to be because of current flow due to potential difference in hot and ground. correct? In this case the current won't return to source because there is no path. This will defy the logic that circuit won't complete unless and until it has return path to source.
 
Last edited:
roy167 said:
Yes, on purpose we are not bonding the transformer and or bulb enclosure etc, no bonding wire is run, just 2 wire. Only transformer neutral is connected to the ground rod. Transformer chasis is not connected to neutral and or ground rod.
Click to expand...
By doing that you gave the neutral a ground reference not bonding any other non current carrying metal doesn't change the fact there is a ground reference, it just leaves those metal items subject to becoming "energized" if there is a fault between them and an ungrounded conductor. Bonding those metal items provides a low resistance path for fault current, and along with overcurrent protection being implemented will allow for opening the circuit in short time when such faults occur. There may still be rise in voltage above ground on those metal items during such faults until the overcurrent device opens the circuit.
 
GoldDigger said:
You have realized a very important thing, namely that the return current of a circuit needs to go not to ground but to the opposite pole of the current source.

In the situation you describe there would be no shock (except for a possible small current resulting from the capacitance between the source and wiring of the circuit to earth.
Click to expand...
I wouldn't want to try that in my bare feet on wet clay..........:D
 
171001-1211 EDT

roy167:

You need to take a course on basic electrical theory. The first would be DC circuits, and the second AC circuits.

Some simple basics are:
1. The sum of the voltages around a closed loop is zero.
2. The sum of the currents at a point is zero.
3. v = i*r, and extended to AC v =i*z.

Consider a 12 V battery floating out in space with a resistive load, no connection to earth. Infinite resistance from either terminal to earth.

You have very dry hands, and using an ohmmeter you measure 1 megohm between your hands. For many dry hand people this is above 500,000 ohms. You grab the battery terminals with your two hands. The current flow is so low you won't feel a tingle.

Change your hands to very sweaty. Now the resistance between hands might be 10,000 ohms or less. Now you should feel a tingle from about 1 mA of current.

Continue with sweaty hands. With no connection to earth for the battery connect your sweaty hands between either terminal of the isolated battery and earth. Now we have an infinite resistance in series with 10,000 ohms for a closed loop load on the battery of infinity, and there is no tingle because no current flows.

Change the previous paragraph to have a wire from the negative terminal to earth. Connect one sweaty hand to the negative terminal and the other hand to earth. No voltage difference, no current, and no tingle. Change the first hand to the positive terminal and now with an assumption that earth resistance is 100 ohms from the battery earth connection point and your hand to earth connection. Loop resistance is about 10,100 ohms. You still have about 1 mA of current, and a tingle.

My soil has a remote earth to ground rod resistance of about 15 ohms. Two such points only add to 30 ohms, thus, less than the assumed 100 ohms above.

.
 
GoldDigger said:
My bad. I misread the OP as saying the transformer neutral was UNgrounded.
Click to expand...
No problem.
I inadvertently electrocuted my dog once.I was being macho holding on to an electric fence with my right hand. He came up sniffed my left hand. I had on rubber boots. He had bare feet on wet grass. It went through me and through him to ground. I think that's the worst shock I've ever had.
 
Besoeker said:
No problem.
I inadvertently electrocuted my dog once.I was being macho holding on to an electric fence with my right hand. He came up sniffed my left hand. I had on rubber boots. He had bare feet on wet grass. It went through me and through him to ground. I think that's the worst shock I've ever had.
Click to expand...
Your dog is dead from the experience? If not, he wasn't electrocuted.
 
ggunn said:
Your dog is dead from the experience? If not, he wasn't electrocuted.
Click to expand...

That was my first thought. I'm really hoping that was the wrong word choice! It would be sad enough that I wouldn't use it for an anecdote!

But then, an electric fence is designed for animals with feet on the ground, right? So electrocution possibility is hopefully designed out of it? I've no experience with them closer than a couple feet. I trust the signage!
 
MAC702 said:
That was my first thought. I'm really hoping that was the wrong word choice! It would be sad enough that I wouldn't use it for an anecdote!

But then, an electric fence is designed for animals with feet on the ground, right? So electrocution possibility is hopefully designed out of it? I've no experience with them closer than a couple feet. I trust the signage!
Click to expand...
The way the DC on an electric fence designed for animal control is pulsed, there is time for the animal to jerk back or fall over, so they only get one pulse.
Electric fences designed for security may not pulse that way and would be a much greater hazard.
 
ggunn said:
Your dog is dead from the experience? If not, he wasn't electrocuted.
Click to expand...
I don't mean my current dog.......:D
Considering the incident was over 50 years ago, yes my dog is dead but not because of that.
And, just to be clear about this, electrocution is not necessarily fatal.

Dictionary definition@

electrocution
ɪlɛktrəˈkjuːʃ(ə)n/Submit
noun
the injury or killing of someone by electric shock.

So yes, based on that definition, my dog was electrocuted...............:p
 
Besoeker said:
So yes, based on that definition, my dog was electrocuted...............:p
Click to expand...

The term electrocute was originally coined in 1889¹ by splicing the prefix electro- into the wordexecute. It originally meant execute (by electric shock). However, its meaning has evolved over time: first to also include accidental death by electric shock and later to include electrical injury,²generally serious in nature. So your use of the word does not fit the original nineteenth century meaning, but is perfectly in line with the broader meaning of the word as it is understood today.
https://english.stackexchange.com/q...-they-have-to-die-or-can-they-just-be-injured
 
Status
Not open for further replies.
Top