3 Phase AC : It consists of R Y B lines, along with one neutral and one ground wire.

If 3 phase load is balanced, and also if generator system is perfectly balanced then EQUAL current flows through all 3 wires and NO CURRENT flows through the neutral line. In case of unbalanced n/w the neutral current wont be zero. But in all the cases no current flows through ground wire.

For 1 Phase AC :

Connection is taken from one of 3 Line wires (R / Y / B) and neutral wire and ground wire. Return path will be neutral wire. (Here the question of balanced or unbalanced doesn't arise.)

Only in case of fault, current flows through earth wire , otherwise no current flows through ground.

Note that Return path is different and ground wire is different.

If no ground wire is provided and unfortunately fault occurs , then at the terminal of fault there will be heavy currents flowing through the fault impedance which caused the fault. Its very dangerous hence ground wire must be provided. If ignored then it can cause death of the personnel as well.

In DC the negative terminal wire acts as a ground though it isn't the ground wire. Whereas in AC There is and must be a ground wire for each line wire of a 3 phase AC system.

In Transmission systems the return path is the neutral i (for AC) and the -ve terminal (for DC).we cannot say it as ground technically,ground is used extensively in electronic circuits to refer the common return path .Note that Neutral and Earth are separate.

3 Phase AC : It consists of R Y B lines, along with one neutral and one ground wire.

If 3 phase load is balanced, and also if generator system is perfectly balanced then EQUAL current flows through all 3 wires and NO CURRENT flows through the neutral line. In case of unbalanced n/w the neutral current wont be zero. But in all the cases no current flows through ground wire.

For 1 Phase AC :

Connection is taken from one of 3 Line wires (R / Y / B) and neutral wire and ground wire. Return path will be neutral wire. (Here the question of balanced or unbalanced doesn't arise.)

Only in case of fault, current flows through earth wire , otherwise no current flows through ground.

Note that Return path is different and ground wire is different.

If no ground wire is provided and unfortunately fault occurs , then at the terminal of fault there will be heavy currents flowing through the fault impedance which caused the fault. Its very dangerous hence ground wire must be provided. If ignored then it can cause death of the personnel as well.

Return path ground is very important for electrical circuit to be completed.In 3 phase circuit (3 phase four wire)if load is balanced the load star point is at the zero potential and hence will not make any difference,but with unbalance load current equal to vector resultant must flow to ground to keep the voltage balance.If star point is not connected to ground, the unbalance voltage will take place and lower load phase voltage will rise and will damaged the applianceses connected,and the higher load phase voltage will reduced ,applianceses will get less voltage and may damaged.The load junction point to neutral(ground) voltage and current(if connected) can be found from its 3 phase voltage and current vector diagrams.For D.C system ground will provide the return path and make the circuit completed.

what's star point ? Bhupendra Desai ·

The topic is complex. You talk about fault current, but of course there are phase-to-earth faults and phase-to-phase faults. Simply speaking the former should let a large current flow to the ground return if there exist one.

Depending on the system we are talking about the ground return is a mix of dedicated conductor, metallic mass (including cable shields and armors, cable duct, and so on, machinery enclosure, etc.), the soil itself.

More specifically, if you think of overhead lines at high voltage a conductor can spark over onto the mast or break and fall on the soil. If the source is tied to ground (neutral to ground, as it is done normally in HV applications), then you see two different fault currents because the fault impedance is different. If the system is insulated from ground then the current due to the first fault is "negligible" (depending on what is the meaning of negligible, e.g. with respect to human safety).

If you think of a railway, AC (namely 5 kV or 25 kV), then they are single-phase and with a far-from-ideal infrastructure: the catenary may break and fall, may touch the rails, the poles, wayside equipment. In this case the ground is treated differently if you are close or far from the catenary (there is a standard, EN 50122), and this implies you have different "ground circuits", that should be called "traction return" or "traction ground", and "system ground", or safety ground.

Sorry for not being more precise, but it's really a complex topic for such systems.

For low voltage, IT systems solve the problem of the ground (as we said before for isolated neutral). Safety and availability are ensured by monitoring with residual current detectors/insulation measurements.

The problem is when several supply and grounding philosophy shall coexist in the same environment: you need a good design, clear hazards and hazard analysis, etc etc.

@ Mubashir Mehdi: the star point is the neutral point, that might be the one coming from the source (such as the center point of the supply transformer windings) as well as a fictious created by yourself (e.g. when you join three voltage transformers in Y connection). Of course the latter is a fictious star or neutral point whose efficacity depends on its own impedance and how you load it.

Plz check the png file attached here. If that(shown in image) is a closed circuit then earth, bulb and moon is also a closed circuit. What I understand Ground is a means to take up free electrons, energized by Battery/source. But the potential difference(between source and ground, moon here) must be there to make electron/charge flow. An example; in planes, when it is far away from earth, the Ground voltage is not 0 volt but 4 to 5 volts.

A thought to add to Fawads question...

Cant we have a charge storage and suddenly release it? then the charges do not need a return path.. For eg. when charged clouds move, they assimilate opposite charges in transmission lines. After the cloud discharges somewhere else, the accumulated charges flow through the system creating a surge..

I do agree that a return path is needed for a power source to operate. But is there any rare exceptions?

For the Earth to moon problem, The bulb should not glow. Why?

1. Voltage is difference in potential of 'X' w.r.t 'Y'. So you cannot simply say that earth is at 0V, without mentioning the reference.

2. Earth is considered a good conductor due to its huge mass. Hence it can be thought of as a big metal ball. Similar is the case for Moon/Mars. and if you do not connect them with another wire, the electrons of the source cannot be replenished.Theoretically, as per your diag, moon just became 50V more positive w.r.t. earth.. only reference changes.

3. If we Consider flow of charged particles like on a lightning , current will flow, but will not because of the 50V Power supply.

Please how to formulate the minimization of load current earth return