Why neutral cable size is half of the phase cable ?
The neutral carry only the “difference” in current between the separate phase wires. For instance, in a single phase 240-volt residential system each 120-volt leg can be a separate circuit. Say total load on one phase is 20 amperes and the total load on the other phase is 25 amperes, the difference current of about 5 amperes is what that is being returned to the transformer windings through the neutral wire. As you can see from the example the neutral wire carries less current. That's why neutral wire are designed smaller size of the phase wire.
The selection of the size of the neutral wire depends on mainly two factors
- Balanced load
- Unbalanced or non linear loads
Balanced load :
In poly phase system ( three phase system), When the current in all three phases are equal known as balance load system. In perfectly balanced load system neutral current is almost negligible. So for the balance load system size of the neutral conductor is small.
Unbalanced load:
In poly phase system, when the current in all three phases are not equal known as unbalanced load system or non linear system. Non linear loads ( geyser, computers, computers , refrigerators) increase harmonics that leads to large neutral current and make unbalanced system. So in case of unbalanced load system the size of neutral conductor could be more than phase conductor .
Frequently asked questions
1. What is neutral conductor ?
Answer: Neutral conductor is an conductor that provides return path for the current and carry unbalanced current.
2. What is the difference between neutral phase and earth wire ?
Answer: Neutral wire provided returning path to the current whereas earth wire is for safety purpose provide low resistance path to fault currents . Phase wire or live wire or hot wire carry current from source to the load .
3. Why neutral of transformer connected to ground?
Answer: The neutral of the transformer is grounded for the protection and safety purposes . When the fault occurs this connection provides a low-resistance path for fault currents to flow to the ground, and helping protecting device to trip and prevent higher voltage build up in the equipments .
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