netutral wire required for housing?

The neutral is used for current flow, and thus can have a potential different from earth ground. The neutral is tied to earth ground at a distribution box at the service entrance to establish a local zero voltage ground potential that can differ from that at the pole distribution transformer. From that point to all outlets in a home or other installation, there should be a safety (earth) ground that normally carries no significant current, and is thus at the same potential as surrounding objects with their own connections to ground, such as water pipes. The separate neutral conductor is designed to carry the same current as the appliance, and may have a significant voltage on it.

This provides enhanced safety. Older electrical installations did not require a separate safety ground, and two slot receptacles were common. If armored BX cable were used, it provided a reasonable safety ground. Then, smaller ground wires were added to Romex cables, and now full size ground conductors are required on the usual household wire sizes. The more recent use of GFCI breakers and receptacles has minimized the need for safety grounds, but they are still required as an additional precaution.

Some appliances, such as electric dryers, may use a three wire connection where the safety ground and neutral are tied together at the appliance. In this case, the main current flow is between the two hot wires, and the third wire only carries a small current used by 120 VAC control components for the dryer.

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Paul