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asad1111
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why during the the distribution of electricity to houses neutral wire is connected to Earth wire?
why during the the distribution of electricity to houses neutral wire is connected to Earth wire?
Studiot said:Check again.
That would be illegal in UK.
In the US the power feed neutral is connected to a supply transformer primary, not to earth.
The local house neutral from the transformer secondary is earthed at the distribution board because the US practise needs is split phase and needs a stable cente zero.
thankyou for your thorough reply but i still don't understand why neutral is connected to ground or Earth because if they don't connect neutral eith Earth we will never get electric shock even if we hold live wire with our bare handsEvil Bunny said:In the US, the center tap (neutral) of the transformer (secondary) supplying your house is connected to a large conductor with a spike on the end that is driven into the ground. One of the two connections on the primary of this transformer (the "return") is also connected to this very same spike in the ground at the utility pole.
This neutral from the center tapped secondary is also connected to your service entrance (distribution board) at your house. Here again, it is also connected to a spike that is driven into the ground next to your house.
This is also the place where the "equipment grounding conductor" is connected with the neutral and the spike and driven into the ground.
Terminology is important here. What I just called the "equipment grounding conductor" is the technical term for this bare copper (or sometimes green insulated) wire in the US. This is more commonly referred to as "ground" or "the ground wire". From what I understand, this is called the "earth wire" in the UK.
These conversations always seem to get confused because of the different terminologies we use on opposite sides of the pond. :-)
asad1111 said:thankyou for your thorough reply but i still don't understand why neutral is connected to ground or Earth because if they don't connect neutral eith Earth we will never get electric shock even if we hold live wire with our bare hands
Studiot said:Do not try the very unsafe experiment of grabbing hold of the line (it is not called live; both are actually 'live').
thank you for your reply so the basic reason of connecting the neutral wire to Earth is to find the electrical faultskeptic2 said:Suppose you have an electrical system in which neither side is grounded as you suggest. With such a system there could be a failure of the insulation and one side of the line could contact ground. Since the other side is not grounded there would be no indication that anything is wrong. If sometime later another point on the same side of the line contacted ground, there still would be no indication of a problem. However if there were a fuse or circuit breaker between those two points, that circuit breaker would now be bypassed and the risk of an electrical fire is greatly increased.
asad1111 said:thank you for your reply so the basic reason of connecting the neutral wire to Earth is to find the electrical fault
asad1111 said:thank you for your reply so the basic reason of connecting the neutral wire to Earth is to find the electrical fault
sophiecentaur said:Only when there is enough current to blow a fuse will the mere grounding of the neutral "detect" a fault. (And that would never reveal a neutral-earth connection fault) The only way to detect a fault reliably is to use a residual current circuit breaker and that would work with or without a grounded neutral and it will spot a fault on either leg. Problem is that RCCBs are active devices and not actually fail-safe.
Studiot said:Now suppose someone was working on the wiring and had switched off the switch ie disconnected the line.
And further suppose that a line- neutral cross fault occurred upline.
The neutral would acquire the line voltage, a potentially lethal situation to anyone working on the wiring.
But this is the whole point of disagreement of which is better. When the ground we stand on is not connected to anything at all why would the live wire touching the neutral make it any more dangerous? What would is actually happening in your scenario is a short circuit up-line.
Averagesupernova said:Concerning what I have put in bold, you cannot be serious. What is a RCCB? Here in the USA we have GFCIs in outlet form and circuit breaker form. They detect an imbalance of current between the hot and neutral. I assume this is what you mean. With a grounded neutral at the service panel, an accidental (partial or full) short from the neutral or hot to the ground in a portable power tool for instance plugged into a GFCI outlet WILL trip this outlet. In a system where the neutral is NOT grounded at the service panel the GFCI is less likely to trip since there is no return path back. The case of the tool as well as the user hanging onto it will be at whatever potential the case is shorted to. A GFCI should not require a grounded neutral at the service to detect the imbalance of current between hot and neutral, but where will the current path be if we don't take steps to make sure it is through the actual earth?
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Almost forgot, I don't think I have ever seen a GFCI fail to open during a fault. It is more likely that they trip unnecessarily.
Averagesupernova said:But this is the whole point of disagreement of which is better. When the ground we stand on is not connected to anything at all why would the live wire touching the neutral make it any more dangerous? What would is actually happening in your scenario is a short circuit up-line.
Studiot said:
What disagreement?
What is better?
sophiecentaur said:The standard way is to use a transformer with three windings. Two are put in series with each of the supply legs, connected in antiphase so as to cancel. When the load is balanced, there is no flux in the transformer so no volts on the third winding. Any imbalance (difference) in the two currents will result in a voltage on this winding. This is used to operate a trip switch. These devices can easily detect 10mA of leakage to Earth, giving good biological protection.
sophiecentaur said:The standard way is to use a transformer with three windings. Two are put in series with each of the supply legs, connected in antiphase so as to cancel. When the load is balanced, there is no flux in the transformer so no volts on the third winding. Any imbalance (difference) in the two currents will result in a voltage on this winding. This is used to operate a trip switch. These devices can easily detect 10mA of leakage to Earth, giving good biological protection.
sophiecentaur said:Where would you put the ammeter?
The problem with Earth faults is that you don't know exactly what path they will travel as there are almost always multiple ground paths. Whether you choose to call them GFCI's or RCCB's or RCD's (residual current devices) or my favorite ELCB's (earth leakage circuit breakers) it's all the same, they all work on detecting a current difference between the live and neutral wires as Sophie previously described.lennybogzy said:well, in series with earth
uart said:The problem with Earth faults is that you don't know exactly what path they will travel as there are almost always multiple paths. Whether you choose to call them GFCI's or RCCB's or RCD's (residual current device) or my favorite ELCB (earth leakage circuit breaker), they all work on detecting a current difference between the live and neutral wires as Sophie previously described.
skeptic2 said:Suppose neither line is grounded. As wire insulation ages it may crack or become worn and allow a small amount of current to flow to ground. If hundreds of homes are connected to the same transformer there could be appreciable current flowing to ground even if all the lines have fuses or circuit breakers.
Someone who knows that both lines are floating, confidently if naively, sits in a bathtub full of water using a hair dryer. As the hair dryer gets wet, a small amount of current may pass from one line in the hair dryer through the person's body to ground where due to the leakage current from many other homes, the current finds a path back to the other line. Where would you put the ammeter in series with ground to prevent such an occurrence?