Why are we not allowed to measure voltage from the neutral wire to the ground wire in an electrical wiring system?

answer:

When measuring voltage in an electrical wiring system, it is **not recommended** to measure voltage from the neutral wire to the ground wire.

This is because the neutral wire is **not** always at zero potential with respect to the ground wire ¹.

The neutral wire is tied to a potential of 0V in comparison to ground with a very low resistance.

This means, that high currents can flow through the neutral wire without any noticeable voltage appearing on the neutral wire ².

If you measure voltage between the neutral and ground wires, you may get a reading that is not accurate and could be dangerous.

It is recommended to measure voltage between the hot wire and either the neutral or ground wire.