Don’t foolishly get grounded and neutral mixed up!

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There are two main purposes for grounding and neutral connection: First, grounding is required according to the operating requirements of the circuit； II. Grounding or zero connection is necessary to ensure the safety of personnel and equipment. Based on their function, they can be divided into four types: a. Working ground ； b. Protective grounding ； c. Protective zero connection ； d. Repeated grounding. I. Working Grounding: In low-voltage power systems with 380/220V voltage, four wires are generally drawn from the power transformer, namely three phase wires and one neutral wire; these four wires are used both for power supply and lighting purposes. Three phase wires are used for power, while one phase wire and a neutral wire are used for lighting. In such low-voltage systems, in order to ensure the reliable operation of electrical equipment under normal as well as fault conditions and to safeguard the safety of personnel and equipment, the system’s neutral point is generally connected directly to ground, which is known as working grounding. The wire that comes from the three windings of the transformer is also called the neutral wire, or zero wire; this point is referred to as the neutral point. The functions of working ground: There are two functions of the working ground; one is to reduce the risk of one phase coming into contact with ground ； Stabilize the system voltage, keep it within a certain range, and reduce the risk of high voltage leaking into the low-voltage circuit. II. Protective Grounding: Protective grounding is a form of grounding carried out to prevent the metal enclosures of electrical devices, the frameworks of power distribution systems, and utility poles from becoming charged, thereby avoiding threats to the safety of people and equipment. Protective grounding refers to a protection wiring method in which the metal parts of electrical equipment that are normally uncharged, but may become charged in the event of damage to the insulating materials or under other circumstances (i.e., the metal structural parts that are insulated from the live parts), are securely connected to a grounding electrode using wires. So, the scope of application for protective grounding: Protective grounding is suitable for ungrounded power grids. In such power grids, regardless of the environment, metal parts that may develop dangerous voltages due to insulation failure or other reasons shall, unless otherwise specified, be provided with protective grounding measures. These mainly include: (1) the metal enclosures, bases of motors, transformers, switching equipment, lighting fixtures, and other electrical devices, as well as the transmission mechanisms connected to them ； (2) The metal frames or reinforced concrete frames of indoor and outdoor power distribution installations, as well as the metal barriers or fences located near live parts ； (3) Metal frames or enclosures of distribution panels, control consoles, protection panels, and distribution cabinets (boxes) ； (4) The metal enclosure of the cable junction box, the metal sheath of the cable, and the steel pipes for wiring ； In addition, the metal towers and reinforced concrete towers of certain overhead power lines, as well as the secondary coils of current transformers, should also be grounded. III. Protective zero connection: Protective zero connection involves directly connecting the metal parts of equipment that are not charged under normal conditions to the system using wires. Adopt protective zero connection to ensure personal safety and prevent electric shock accidents. The working principle of protective zero connection is a electrical safety measure that connects the metal casing of electrical equipment to the neutral wire in the power grid in order to protect human safety. In a neutral-connected power grid with a voltage below 1000 volts, if the metal casing of electrical equipment becomes charged due to insulation damage or some other accident, resulting in a single-phase short circuit between the phase wire and the neutral wire, the protective devices on the circuit (circuit breakers or fuses) will activate immediately to cut off the power supply. This prevents the metal parts of the equipment from being exposed to dangerous voltages for an extended period of time, thereby ensuring personal safety. In a polyphase AC power system, the neutral point of the star-connected windings is directly grounded, bringing it to the same potential as the ground, that is, to zero potential. The wire leading from the grounded neutral point is called the neutral wire. On electrical equipment powered by the same power supply, it is not permitted for some of the equipment to use protective neutral connection while another part uses protective grounding (see Grounding). Because when the enclosure of a device connected to ground for protection becomes charged, if its grounding resistance r′D is high, the fault current ID is not sufficient to trigger the protective device. Due to the presence of the operating resistance rD, a voltage U0=IDrD persists on the neutral wire. As a result, a dangerous voltage U0 remains on the enclosure of devices connected to ground for protection for an extended period of time, posing a risk to human safety. IV. Difference between working grounding and protective neutral grounding. Working grounding refers to the excess electricity generated during electrical operation; in order to prevent this excess electricity from causing harm to people, it is directed into the ground, and this is what is meant by working grounding. Any grounding that is necessary for the proper operation of equipment is considered working grounding. If it is not connected, the device cannot operate. For example: the neutral point of the transformer is grounded. The protective neutral wire – which is actually the ground wire – is the wire that allows the circuit breaker to trip in a timely manner when it comes into contact with an object, thereby preventing injuries; this is what is meant by the protective neutral wire. Both wiring methods play an important role in protecting personal safety. V. Differences between protective grounding and protective neutral grounding 1. Different principles: Protective grounding is used to limit the voltage of equipment in case of leakage to ground, ensuring it remains within safe limits. In high-voltage systems, protective grounding not only limits the voltage with respect to ground but also, in certain situations, triggers the operation of protective devices in the power grid. Protective neutral grounding enables leakage current from equipment to cause a single-phase short circuit, thereby activating the protective devices on the circuit and cutting off the power supply to the faulty equipment. Furthermore, in a protective zero-system, the protective neutral wire and repeated grounding can also limit the voltage to ground in the event of equipment leakage. 2. Different application scopes: Protective grounding is applicable to both high-voltage and low-voltage power grids that are not grounded, as well as to low-voltage power grids that have other safety measures in place (such as the installation of leakage protectors); protective neutral grounding is only applicable to low-voltage power grids whose neutral point is directly grounded. 3. Different line structures: If protective grounding is used, there can be no working neutral wire in the power grid, with only a protective grounding wire being present; if protective earthing is employed, then a working neutral wire must be installed, which is used for earthing protection. The protective neutral wire shall not be connected to switches or fuses. When switching devices such as fuses are installed on the working neutral wire, a separate protective earth wire or neutral wire must be provided.