Please help to find the answer of the following MCQ question. Thanks in advance
The cable to an electric cooker contains a live wire, a neutral wire and an earth wire.
When the cooker is working correctly, in which wires are the currents equal?
A – the live, the neutral and the earth
B – the live and the earth only
C – the neutral and the earth only
D – the neutral and the live only
Answer is D The Neutral and Live only
LIVE, NEUTRAL AND EARTH WIRE
A ‘live’ or ‘hot’ wire is a wire that is connected to a power source. This wire supplies voltage to a load (light bulb, hair dryer, etc.). When the load is also connected a neutral or another live wire this becomes a path for the flow of current (amps) known as a circuit.
Neutral is return path for an AC circuit which is supposed to carry current in normal condition. This current may be because of many reasons, primarily because of phase current imbalance and some time because 3rd and 5th harmonics also.
There may be others reasons too but the magnitude of this current is in fraction of phase current and in few case it can be even double of phase current. So Neutral wire is always assumed to be charged (in active circuit). This neutral wire is given to ground (by grounding) to make the second terminal of neutral wire at zero potential.
Earth or Ground
Earth or Ground is for safety concerns against leakage or residual currents on the system via least resistance path. While phase and neutral is connected to main power wiring, earth may be connected to body of equipment or to any system which in normal condition doesn’t carry current but in case of some insulation failure, is supposed to carry some minor current.
This current is not directly coming from live or phase wire, but is from secondary links which was not in touch with live system in normal condition. This current is usually much lesser than main line current or phase current and mostly is in order of mA. But this leakage current is good enough to kill someone or may risk fire. Such current are being provided a low resistance path and sent to earth via earth wire.
Because of the difference in application we never mix grounding of neutral and earth. However both are made grounded (of-course the process may be different). If both will be mixed then the earth wire which is not supposed to carry any current in normal condition , may have some charges across and will become hazardous.
The circuitry in three phase system is a little different than single phase system.
Interestingly, neutral and earth are both grounded wires with one subtle difference, that is neutral is grounded where the transformer is located and earth is a local ground beside a house with an access to electricity.