# How to calculate the neutral wire size of a home (department)?

I know that in electrical grid, Neutral wire is a non current carrying conductors so its cross section area is smaller than the cross section area of the live conductors. I think it has half of size of the live conductor.

Is this rule valid for a department or a small home that uses 1 phase only? If I'm buying the neutral cable for a home, Should it be less that or equal live wire ?

My country does not have grounding system. The wall outlets have two ports only (220V / 50Hz). But the neutral of distribution transformers is grounded.

Thank you,

• In a properly wired arrangement, the neutral conductor will carry exactly the same current as the live conductor. Commented Feb 29, 2016 at 17:23
• For single phase, the return current is carried by the neutral. You need equal size conductors. Half- or third-sized neutral applies only to three phase. Commented Feb 29, 2016 at 17:25
• @uint128_t Unless of course every home appliance comes with a 15m copper rod to hammer into the ground. :-P Jeez, would I hate having a tile floor in that system! Commented Feb 29, 2016 at 18:46

## 2 Answers

In the US, home electrical power is actually delivered in the form of 240 VAC center-tapped, with the center the neutral, and 2 hot lines at 120 VAC each, but 180 degrees out of phase. The current in the neutral will depend on the load balance of the various power circuits connected to the two hot lines. There is nothing preventing all of the loads on one hot line being active, while none of the loads to the other hot line being connected. In this case, the neutral current will equal the hot current. For instance,

simulate this circuit – Schematic created using CircuitLab

• Why did you assume the neutral conductor will have 0 amps running through? would not the neutral short out one of the two hots in this specific circuit ? Commented Jul 29, 2018 at 14:04
• @Gold_Sky - I don't even know how to answer your question. If Hot1 and Hot2 are equal but opposite wrt neutral (which is what the center tap guarantees), the voltage drops across the two loads will be identical, and the voltage between the junction and neutral will be zero volts, so no current flows. And I simply don't see why you think neutral can "short out one of the two hots". The idea makes no sense. Commented Jul 29, 2018 at 18:35

You appear to be talking initially about the neutral wire in a 3 phase distribution system and given certain constraints on load imbalances, the "star point" imbalance current is usually a lot smaller than either of the three individual phase currents.

For a single phase system (even if it is derived from a 3 phase system) you must make the neutral wire the same diameter as the live wire because it conducts the same current.