The Effect of Ground Resistance on Electrical Circuits

[r.vittalkiran]

Why does a 220V supply current flows through the Ground(i mean Earth), whereas when i connect a 12V battery and a small LED/bulb to it and the other terminal to ground(earth), why won't the bulb glow? My question here is: If it is possible to glow a 220V rated bulb by connecting it b/w phase and ground, why is it not possible to glow a bulb(rated 12v) b/w positive of a battery and ground?

 

[shakgoku]

its not possible. Because we can't change Earth's potential by using small voltages like 220V. By convention we take Earth at 0 potential. So due to potential difference current flows between the phase and the earth. But no current flows into the bulb from earth(no potential difference). So bulb does not glow.

 

[r.vittalkiran]

its not possible. Because we can't change Earth's potential by using small voltages like 220V. By convention we take Earth at 0 potential. So due to potential difference current flows between the phase and the earth. But no current flows into the bulb from earth(no potential difference). So bulb does not glow.

But there needs to be a potential difference b/w them, whether the voltage is Big/Low.

 

[nasu]

Why does a 220V supply current flows through the Ground(i mean Earth), whereas when i connect a 12V battery and a small LED/bulb to it and the other terminal to ground(earth), why won't the bulb glow? My question here is: If it is possible to glow a 220V rated bulb by connecting it b/w phase and ground, why is it not possible to glow a bulb(rated 12v) b/w positive of a battery and ground?

It's possible, in principle. You have to connect the negative of the battery to the ground too, in order to close the circuit. And the "grounds" should be good enough (low resistance).
I think the first telegraphs were using only one aerial wire and they will close the circuit through the ground. And they used batteries at that time.

 

[r.vittalkiran]

It's possible, in principle. You have to connect the negative of the battery to the ground too, in order to close the circuit. And the "grounds" should be good enough (low resistance).
I think the first telegraphs were using only one aerial wire and they will close the circuit through the ground. And they used batteries at that time.

Hi nasu,
I found the same through my research, can i get source of your answer. If that is true, then where is neutral wire grounded(for it to complete/close the circuit).
I have a small confusing between various sources.

 

[Born2bwire]

Hi nasu,
I found the same through my research, can i get source of your answer. If that is true, then where is neutral wire grounded(for it to complete/close the circuit).
I have a small confusing between various sources.

Yeah, this is my recollection too on how early telegraph operated. There was a single signal wire and the circuit was closed on an Earth ground. This was ok for short runs but as they increased the distance they found problems with the system. One problem being that the Earth is not at a uniform potential and that there can be a voltage difference across the Earth (but over distances of say tens or hundred miles or so) and thus the ground reference between operators could be very different. Then there was the introduction of the wave physics that such long distances introduced.

 

[shakgoku]

As i have said, its not possible with low voltages like 220V,
You need over a thousand volts to make the current flow though the circuit because Earth has a very high resistance.

 

[schip666!]

As i have said, its not possible with low voltages like 220V,
You need over a thousand volts to make the current flow though the circuit because Earth has a very high resistance.

I did this experiment because, A) I didn't believe, and B) everyone was arguing about it on Craigslist-Science...

I buried one wire from the bulb in the ground about a meter from my earthed-electrical-service-entrance box (in dry but iron rich soil). I attached the other wire of the bulb to the HOT wire of the electric power, in this case USA 120v. (In the interest of safety, if you have to ask how I did all of this you should not attempt to repeat this experiment without adult supervision). The bulb -- a small 7 watt christmas-tree kinda thing -- glowed dimly. I was surprised.

There is a finite resistance through just the "earth" connection. It lit the bulb but is large enough that I wouldn't rely on it to power my space heater.

In the case of the 12v system, with one lead well "grounded", I would expect the resistance to be high enough to reduce the current flow to less than what's needed to get the bulb to glow. But you should be able to measure some small current flow with a meter.

 

[nasu]

As i have said, its not possible with low voltages like 220V,
You need over a thousand volts to make the current flow though the circuit because Earth has a very high resistance.

This does not make sense even if one admits that the Earth has a high resistance.
You don't need a threshold voltage to have a current in a pure resistive circuit. The current may be small, but is there.

Regarding the Earth's resistance, the values I found are of the order of a few ohms, for distances of the order of a few feet between the electrodes.
for example :http://www.kilowattclassroom.com/Archive/AN0009.pdf

However the main component to the resistance comes from the contact resistance between the electrode and the ground. If you find that the resistance is too high it probably means a poor grounding.

 

[NobodySpecial]

As i have said, its not possible with low voltages like 220V,
You need over a thousand volts to make the current flow though the circuit because Earth has a very high resistance.

Then I suggest you hold a 220V line while connected to ground - say a nice wet concrete floor (actually I suggest you don't do this!)

 

[shakgoku]

Yes, there is nothing like a threshold voltage. What I meant was to practically use use it to transmit power (as an alternative to using transmission wires), we need 1000 V (according to information given in wikipedia)

 

[r.vittalkiran]

I did this experim........me small current flow with a meter.

In that case, ---IN POWER TRANSMISION(110,220,ETC)---
If its possible with your house hold power supply, the neutral wire needs to be grounded, for circuit/path to complete. So where exactly is it GROUNDED(Earth).

@ above

If it won't work properly for low voltages... Then did those initial telegraph system used very high voltages?

 

[vish_al210]

Why does a 220V supply current flows through the Ground(i mean Earth), whereas when i connect a 12V battery and a small LED/bulb to it and the other terminal to ground(earth), why won't the bulb glow? My question here is: If it is possible to glow a 220V rated bulb by connecting it b/w phase and ground, why is it not possible to glow a bulb(rated 12v) b/w positive of a battery and ground?

Hi did you connect the other led/bulb terminal to ground. And by ground are you talking about the ground terminal in your power socket (the Earth line is connected through a metal rod, a few meters into Earth into a soakpit, which regulates the resistivity of the rod.) but if you just touch one battery terminal on the ground surface and the other terminal to led, the other led terminal just on to the ground surface.. I don't think ur setup will work as the resistance of base dust is in mega ohms.. remember in college or school u would have used a megger to find the resistance.
Well if you have used the ground terminal from the socket. It is just like taking a conductor and joinging two wires through it, that should work.. but the Earth potential does not come into play. in this case make sure that the led direction is correct.

If you wish to include ground potential then use ground of one house to the +ve battery terminal, the -ve terminal of Battery to Cathode of LEd, Anode of LED to the Earth terminal of another house (another ground location) only then u will be using the ground as the conductor.

 

[r.vittalkiran]

@vish_al

yep... that's same conclusion as that from the previous posts... :|

I did this experim........me small current flow with a meter.

In that case, ---IN POWER TRANSMISION(110,220,ETC)---
If its possible with your house hold power supply, the neutral wire needs to be grounded, for circuit/path to complete. So where exactly is it GROUNDED(Earth).

@ above

If it won't work properly for low voltages... Then did those initial telegraph system used very high voltages?

 

[NobodySpecial]

If it won't work properly for low voltages... Then did those initial telegraph system used very high voltages?

No. But in a telegraph system you don't want an current to flow, you want a very high impedance detector at the receiving end so you don't need to put lots of power in

 

[vish_al210]

The neutral line is called neutral only if is earthed.. otherwise it is also phase as it carries a potential with reference to earth. The neutral line is grounded at the powerstation and at each subsequent sub-station and also at intermittent distribution points..to maintain its potential neutral wrt the earth. So even if you do not connect the neutral line to the Earth potential, the potential of the neutral wire would only be a few volts above the Earth's potential.
To complete a circuit you do not need the Earth line connection. because irrespective of you grounding the neutral line the potential between the two wires is 230VAC.
By grounding it does not mean that the wire is just touched on the suface of the Earth or ground (I am talking geographic Earth crust and not the ground terminal..)
To gain//access the Earth's potential you need to place the conductor a little deeper a few feet or meters and to reduce the junction resistance in our homes we add a salt mixture and the pit is watered regularly to avoid changes in junction resistance.

 

[vish_al210]

And it will work at low potentials also.. well. if u have doubts do an experiment..
Be careful with the experiment, and please do under adult supervision if legally u r a minor. And anyways.. do in supervision .. u know just in case things get ugly...
Take a normal bulb (15 - 100W..well as per choice//availability..) and wire it to ur AC mains.. (any freq/voltage as per country..it is ok.)
Now turn On the switch, check if the bulb glows..
Now turn off the bulb..
strip the wire at two places in one of the wires connected to the socket. well in the first case use the neutral wire..(it doesn't matter as I recomment you to repeat the experiment with the other terminal as well.)
Now connect the battery +ve to one stripped section of the wire. connect the led Anode to the other peeled/stripped section of the wire, connect the cathode of the LED to the -ve terminal of the battery. ur LED should glow.
Now turn On the switch of the AC lamp, the LED still glows..
Now turn off the lamp switch.
Now if u r in India, just rotate the 2 pin plug 180 degrees and connect back to the socket, (reversing the neutral and phase lines) or if u have used a 3 pin plug or are in a country where u have special terminal plug socket combinations, remove the battery and anode connections made and tape the stripped sections of the wire, now strip the other terminal wire in two sections and repeat the experiment.
You would observe the same.
Please take care to ensure that the battery and LED are connected through only one line.. i.e., between one end of AC lam and AC plug/socket. and never conatcted with both wires or lamp terminals or in other words across the lamp or the plug. This would result in the AC potential being fed to the battery and the LED. That would be dangerous.

 

[schip666!]

In that case, ---IN POWER TRANSMISION(110,220,ETC)---
If its possible with your house hold power supply, the neutral wire needs to be grounded, for circuit/path to complete. So where exactly is it GROUNDED(Earth).

I think grounded is an overloaded term here...

We often blithly say, "...and ground the other side of the circuit..." meaning connect it to the power supply return path. If the supply is a battery, usually, we will use the PLUS end as the supply line -- thank Ben Franklin for this -- and the NEG end as the "ground" return.

For household power in the USofA the feed from the power pole is nominally "two-phase" 220v with a "neutral" line, making two 110v "legs" each 180deg out of phase with each other. The neutral is basically the center tap of the transformer on the pole. For safety reasons it is attached to a "ground rod" stuck into the Earth at the pole AND at the service entrance box (where the main cutoff switch and meter are). If this was not done, the voltage between any power wire in your house, hot and neutral, would be floating and could have a (even more) dangerous potential between it and (for instance) your kitchen sink. Think of a close lightning strike inducing voltage in your wiring.

There is also, in most houses, a separate "ground" wire which does not normally carry any current. It is there as an emergency sink when a hot line shorts to something it shouldn't. The ground and neutral wires are connected together at the service entrance where the Earth ground rod is.

Given this power topology and the fairly low resistance of the Earth's crust, you can get current flow between the "hot" lines and anything touching the Earth. That current is low enough that it can't really power anything but can be dangerous, especially if things are wet and conduct better. However it's probably less dangerous than letting everything float...

 

[rcgldr]

At our home (USA), at the nearest tranformer box, electricity comes in at 6900 volts into a step down transmitter that outputs 220 volts. There is also a center tap on the 220 volt side to provide a "neutral" (so each side of the 220 volts and the neutral provide 110 volts), and it doesn't appear to be grounded. At each household, there's a 4th line that is grounded used for the 3rd pin in a "grounded" plug. For 110 volt outlets, the two 220 volt lines are somewhat evenly distributed thorughout the houshold, sharing the common center tapped neutral line from the transformer. Inside our home, I measure about .3 to .4 volts between "neutral" and "ground".

Ground Fault Interruptor plugs monitor to see that current between the two 220 volt lines or a single 220 volt line and the neutral (center tapped line) are equal, if not, then current is flowing between one of the lines and Earth ground (or the "wrong" line), and the GFI device shuts off the current for safety.

 

[vish_al210]

As i have said, its not possible with low voltages like 220V,
You need over a thousand volts to make the current flow though the circuit because Earth has a very high resistance.

Actually the Earth is the potential bank in this circuit. So current can flow. See the resistance is between the Earth potential, soil surface and the conductor u r trying to place. That resistance of the Earth's (geographical and not electrical) is the issue and not the potential.
If you make a proper ground connection, then try this under strict adult supervision or ask ur electrical maintenance man to do it for you.
Open the neutral connection that u get form your electricity supplier from the junction box. I mean isolate it and tape that terminal.
Now your neutral lien from the Electricity supplier is no longer connected to your house connection. (Dont turn on any costly electronic equipment.. don't know why but most say that they fail)
Now turn on any AC lamp that u have in your house.
It will glow.., measure the potential using a voltmeter and check across the phase lien and the actual Earth line which is now running along all the neutral and Earth lines...

 

[vish_al210]

One reason for this to happen is that all along the neutral line potential has been maintained similar to the Earth's potential and the Earth's potential is only a few volts +- from the neutral line's (mandatory to maintain this condition to <10V variation). This is done by grounding the neutral line at multiple points along the transmission system from the power generation station to your house.
And the Earth is the biggest potential bank. So don't worry about the return path.. the transmission system will have a current path from the Earth to the neutral and from the Earth to the phase hence completing the circuit.

 

[vish_al210]

Well as stated earlier, in the normal power transmission case, the electrical circuits do not need one line to be connected with the Earth's potential for circuit completion, but as a safety measure..
In case u need to form a circuit using the phase line and the Earth's potential, then you need to create ur Earth terminal (a tapping point to Earth potential).
Dig a few feet/ meters deep (actually recommended is 14 ft//4 meters) or as per your convenience, but I 'd recommend atleast a 3 ft or a meter, now plant an aluminium rod/bar/wire into it. pour little water and cover with the soil adding water in small quantities.. the soil needs to be wet, not sludgy.
Now take an AC bulb, wire one end of the bulb to your house phase line, through a switch, while keeping the switch off. Wire other end of bulb to the newly created Earth terminal. Now turnthe switch On. The lamp will glow.
Now for your battery experiment, you need to create one more Earth terminal, as discussed above.. NOw you have two points. connect one end of battery(+ve) to Ground, other end of battery (-ve) to led(Cathode), the Anode of LED to the other Earth terminal, Your circuit should get completed. But please do not try using a 1.5V pencil battery, use a car battery(12V or 24V) or atleast a 9V battery.
The reason is depending on the Earth electrode contact resistance the current in the circuit may drop, also a voltage drop will happen. General led primarily require atleast 10mA to turn the LED On.
Better still remove LED and instead connect a Voltmeter(Multimeter in Voltage range) to measure the voltage.

 

[r.vittalkiran]

@ vish_al210!
Pretty BIG... will have to read it continually for me to understand :)

Why is it so important to ground the neutral terminals over and over again?
1st ques is why should it be grounded if its possible to draw current without that?
https://www.physicsforums.com/library.php?do=view_item&itemid=301

Suppose if the 'Neutral wire was not grounded' , did it cause no Electric Shock?

 

[rcgldr]

Suppose if the neutral wire was not grounded

As mentioned in my earlier post, the final transformer stage at our home has no neutral wire going into the transformer. There are only two large wires going in at 6900 volts, two wires going out at 220 volts, and a third, non grounded line center tapped from the output side of the transformer to create the "neutral". I assume that some type of "neutral" grounding is done further back to keep the final neutral within the 10 volt limit mentioned above. As also mentioned I measured the difference between neutral and ground to be .3 to .4 volts at our home.

 

[vish_al210]

@ vish_al210!
Pretty BIG... will have to read it continually for me to understand :)

Well All the best with that ... ;)
But seriously...please do...

Why is it so important to ground the neutral terminals over and over again?

It is grounded at all points where the voltagemay be referenced to earth. To keep ur home safe it is sufficient for you to Earth your neutral line at your home alone. The line need not be earthed at multiple points along the distribution system. But it is to ensure the safety of all people at different points of the distribution cycle that the line is grounded/earthed at multiple points.

1st ques is why should it be grounded if its possible to draw current without that?
https://www.physicsforums.com/library.php?do=view_item&itemid=301
Suppose if the 'Neutral wire was not grounded' , did it cause no Electric Shock?

And as for, the reason for one of the power lines coming to your home to be grounded is to make one in reference to the Earth's potential, which is what u tend to carry when standing on bare earth, barefoot.
If one of the lines is not earthed then both lines carry a potential wrt the Earth's potential, which can be dangerous incase of any faults.
The Earth line is finally connected to the body of any device that gets connected to the system. Thereby hlding the devices body at a potential simillar to the ground. if any fault/leakage to body happens then it is transferred to the neutral line (as both neutral and earthline are connected). If a fuse is connected to the Earth line then it blows before any further damage is caused. Also at such times when there is body leak the ground line helps in avoiding the risk of shock to an unsuspecting user.
Also if neutral is not connected to Earth at all, then the neutral line would also be carrying a potential difference wrt the Earth (called a floating potential) and would cease to be neutral wrt the Earth's potential, causing a direct shock hazard if user were to touch either phase or neutral.
Also as the Earth and neutral are connected the switch is sufficient to be of single pole - two way across the phase line. Else we would have required to have a two pole switch isolating both phase and neutral to protect the user.
FYI:: IN our office I was astounded to find the isolated ground of the oscilloscope to have a potential of 185V wrt the ground of another isolated device.
Also the potential difference is not influenced (at least not more than a couple volts) if the potential of one of the lines is tied to another (to either raise or lower its individual potential).
hence regardless of Earthing or not, the potential across the phase and neutral remain to be ~230VAC or ~110VAC depending on the system.

 

[david90]

Why does the power company ground their neutral connection @ the power plant and at substation? Correct me if I'm wrong, the reason why there's a shock hazard in the event of a broken wire/insulator is because the grounding @ the substation (assuming there's no ground connection @ house)

 

[davenn]

As i have said, its not possible with low voltages like 220V,
You need over a thousand volts to make the current flow though the circuit because Earth has a very high resistance.

please don't make such misleading statements that are so, so incorrect!

it is possible with much lower voltages and as others have said it is partly dependent on the ground resistance
In my long years with a telephone company many of our old outlying subscribers had just a single wire line to the house running over many 10's on kilometres the return path back to the telephone exchange was via the ground.

In Australia and New Zealand (and maybe other countries) we have 230/240VAC mains
The neutral line is earthed at the building switchboard.

Dave