Why neutral is called neutral?

Answer 1

This comment applies to 3 phase, interior building Transformers: The "home" voltage (120/240) can be considered to be "two thirds" of the options described below, even though the situation with that voltage is somewhat different).

There are two common types of building distribution transformers (there is a third outside/exterior type that is common, but it is a variation of one of the first two). The transformers are wired in one of two configurations. The two configurations are called "delta" and "wye".

Each of the types has three "cores", which are essentially large laminated slices of iron with (a lot) of wire wrapped around them. Might be easier if you try to visualize the following:

Each core is one large, rectangular peice of iron. A copper wire "starts" at one end of the core and wraps around it many times to "finish" at the other end of the core. Imagine one core with a wire tail coming off both the start and finish end.

For a delta transformer: Each of their cores is connected one end tail wire to the start tail wire of one of the other transformer cores. If you "do" this just like that (one start to one end using all three cores and not "tripling" wire connections at any point) you have somthing that looks like a triangle. This is called a delta wired configuration, and does not "create" a neutral.

If you measure voltage from one"corner" to another "corner", you get the same voltage no matter what combination of two "corners" you choose to measure with your two meter leads. (There are grounding conditions where this is not true, but that is beyond this scope).

The other configuration of transformer is called a wye transformer. In this configuration, each core has one end wire solidly connected to BOTH OF THE OTHER "END" WIRES. That leaves something that looks like the letter Y: All cores connected at one point (the center point, or NEUTRAL), and each core has one end wire "open", that is, not connected to any other wire.

In this configuration: The center wires are considered "one wire/point" (they cannot be measured one "end wire" to another "end wire".

If you measure any "start/open/unconnected" wire to another "start/open/unconnected" wire you get a stable voltage, point to point no matter which two points you measure with your two meter leads.

However: If you measure from any open end to the "closed/center/point" connection, you get a different, lower voltage.

This is called the "hot to neutral voltage". The "hot to neutral voltage" multiplied by 1.732 gives you the "open point to open point" voltage.

Anyway, long way around: The center point on the wye, where all the three cores connect, is called the "neutral (point)". At this point, the cores can be (and in most cases, must be) connected directly to earth/ground WITHOUT ANY VOLTAGE POTENTIAL, that is, without a spark/flash, because all the core voltages here "neutralize" each other.

Another way of putting this: Something normally conductive (another wire, a tool, etc.)could accidentally "touch" the "neutral point", no current (theoretically) would flow through it because all the core voltages are "neutralized" here.

Hope that helps.