Ground and neutral
The neutral conductor receives and returns alternating current to the supply during normal operation of the circuit; to limit the effects of leakage current from higher-voltage systems, the neutral conductor is often connected to earth ground at the point of supply.
A ground conductor only carries significant current if there is a circuit fault that would otherwise energize exposed conductive parts and present a shock hazard.
Under certain conditions, a conductor used to connect to a system neutral is also used for grounding (earthing) of equipment and structures.
Ground or earth in a mains (AC power) electrical wiring system is a conductor that provides a low-impedance path to the earth to prevent hazardous voltages from appearing on equipment (high voltage spikes).
Grounding is also an integral path for home wiring because it causes circuit breakers to trip more quickly (ie, GFCI), which is safer.
Adding new grounds requires a qualified electrician with knowledge particular to a power distribution region.
The differences are that the conductors may be separate over their entire run from equipment to earth ground, or may be combined all or part of their length.
In the TN-S system, separate neutral and protective earth conductors are installed between the equipment and the source of supply (generator or electric utility transformer).
In the TN-C system, a common conductor provides both the neutral and protective grounding.
Very small voltages, not usually perceptible to humans, may cause low milk yield, or even mastitis (inflammation of the udder).
[3] So-called "tingle voltage filters" may be required in the electrical distribution system for a milking parlour.
In the United States, the cases of some kitchen stoves (ranges, ovens), cook tops, clothes dryers and other specifically listed appliances were grounded through their neutral wires as a measure to conserve copper from copper cables during World War II.
This practice was removed from the NEC in the 1996 edition, but existing installations (called "old work") may still allow the cases of such listed appliances to be connected to the neutral conductor for grounding.
(Canada did not adopt this system and instead during this time and into the present uses separate neutral and ground wires.)
In North American and European practice, small portable equipment connected by a cord set is permitted under certain conditions to have merely two conductors in the attachment plug.
Portable appliances never use the neutral conductor for case grounding, and often feature "double-insulated" construction.
In places where the design of the plug and socket cannot ensure that a system neutral conductor is connected to particular terminals of the device ("unpolarized" plugs), portable appliances must be designed on the assumption that either pole of each circuit may reach full main voltage with respect to the ground.
[4] Such distribution systems were monitored by permanently installed instruments to give an alarm when high leakage current was detected.
Commonly the system neutral is connected to the star point on the feeding transformer.
It is common on larger systems to monitor any current flowing through the neutral-to-earth link and use this as the basis for neutral fault protection.
The connection between neutral and earth allows any phase-to-earth fault to develop enough current flow to "trip" the circuit overcurrent protection device.
In a three-phase linear circuit with three identical resistive or reactive loads, the neutral carries no current.
In some jurisdictions, the neutral is allowed to be reduced in size if no unbalanced current flow is expected.
If the neutral is smaller than the phase conductors, it can be overloaded if a large unbalanced load occurs.
The current drawn by non-linear loads, such as fluorescent & HID lighting and electronic equipment containing switching power supplies, often contains harmonics.
In split-phase wiring, for example a duplex receptacle in a North American kitchen, devices may be connected with a cable that has three conductors, in addition to ground.
The white serves as a common neutral, while the red and black each feed, separately, the top and bottom hot sides of the receptacle.
Typically such receptacles are supplied from two circuit breakers in which the handles of two poles are tied together for a common trip.
The common trip prevents overloading of the shared neutral if one device draws more than rated current.
[citation needed] Extra ground connections on a neutral conductor may bypass the protection provided by a ground-fault circuit interrupter.
