Does The Neutral On A Service Feed Need An Insulator

Basis and neutral are excursion conductors used in alternating current electrical systems. The ground excursion is connected to earth, and neutral circuit is usually connected to footing. Every bit the neutral bespeak of an electrical supply organisation is ofttimes connected to earth footing, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a organization neutral is also used for grounding (earthing) of equipment and structures. Electric current carried on a grounding conductor tin can outcome in objectionable or dangerous voltages appearing on equipment enclosures, so the installation of grounding conductors and neutral conductors is carefully defined in electrical regulations. Where a neutral conductor is used as well to connect equipment enclosures to earth, care must exist taken that the neutral conductor never rises to a high voltage with respect to local footing.

Definitions [edit]

Ground or globe in a mains (AC power) electrical wiring system is a conductor that provides a low-impedance path to the world to prevent hazardous voltages from actualization on equipment (high voltage spikes).^{[ citation needed ]} The terms ground and world are used synonymously in this section; footing is more common in N American English, and earth is more than common in British English. Under normal conditions, a grounding conductor does not carry current. Grounding is too an integral path for home wiring because it causes circuit breakers to trip more quickly (ie, GFI), which is safer. Adding new grounds requires a qualified electrician with knowledge particular to a power distribution region.

Neutral is a circuit conductor that ordinarily completes the circuit back to the source. Neutral is usually connected to ground (earth) at the main electric panel, street drib, or meter, and also at the final pace-down transformer of the supply. That is for elementary single panel installations; for multiple panels the state of affairs is more complex. In a polyphase (unremarkably three-phase) AC organisation, the neutral usher is intended to have similar voltages to each of the other circuit conductors, only may carry very little electric current if the phases are balanced.

All neutral wires of the same earthed (grounded) electric system should have the aforementioned electric potential, because they are all connected through the system ground. Neutral conductors are usually insulated for the same voltage every bit the line conductors, with interesting exceptions.^[i]

Circuitry [edit]

Neutral wires are usually connected at a neutral bus within panelboards or switchboards, and are "bonded" to globe ground at either the electrical service entrance, or at transformers within the system. For electric installations with split-phase (iii-wire unmarried-stage) service, the neutral betoken of the arrangement is at the center-tap on the secondary side of the service transformer. For larger electrical installations, such as those with polyphase service, the neutral point is usually at the common connection on the secondary side of delta/wye connected transformers. Other arrangements of polyphase transformers may effect in no neutral betoken, and no neutral conductors.

Grounding systems [edit]

The IEC standard (IEC 60364) codifies methods of installing neutral and ground conductors in a building, where these earthing systems are designated with letter symbols. The letter of the alphabet symbols are mutual in countries using IEC standards, just North American practices rarely refer to the IEC symbols. The differences are that the conductors may be separate over their entire run from equipment to earth ground, or may exist combined all or function of their length. Different systems are used to minimize the voltage difference between neutral and local earth ground. Electric current flowing in a grounding usher volition produce a voltage drib along the usher, and grounding systems seek to ensure this voltage does not attain unsafe levels.

In the TN-S system, separate neutral and protective world conductors are installed between the equipment and the source of supply (generator or electric utility transformer). Normal circuit currents flow only in the neutral, and the protective earth usher bonds all equipment cases to world to intercept any leakage current due to insulation failure. The neutral conductor is connected to globe at the building signal of supply, merely no common path to ground exists for circuit electric current and the protective conductor.

In the TN-C system, a common conductor provides both the neutral and protective grounding. The neutral conductor is continued to earth ground at the indicate of supply, and equipment cases are connected to the neutral. The danger exists that a broken neutral connection volition allow all the equipment cases to rise to a unsafe voltage if any leakage or insulation fault exists in whatsoever equipment. This can be mitigated with special cables only the cost is then higher.

In the TN-C-S system, each piece of electrical equipment has both a protective footing connection to its instance, and a neutral connection. These are all brought back to some mutual point in the edifice system, and a common connection is then made from that point dorsum to the source of supply and to the world.

In a TT system, no lengthy common protective ground conductor is used, instead each article of electrical equipment (or building distribution system) has its own connection to world basis.

Indian CEAR, Rule 41, makes the following provisions:

The neutral conductor of a iii-phase, four-wire system and the middle conductor of a 2- phase, 3-wire organization must have at to the lowest degree 2 split and distinct earth connections with a minimum of 2 unlike earth electrodes to have a satisfactory globe resistance
The world electrodes must be interconnected to reduce earth resistance
The neutral conductor shall also be earthed at one or more points forth the distribution system or service line in addition to any connection at the user stop

Combining neutral with footing [edit]

Stray voltages created in grounding (earthing) conductors by currents flowing in the supply utility neutral conductors tin can exist troublesome. For case, special measures may be required in barns used for milking dairy cattle. Very pocket-sized voltages, not usually perceptible to humans, may cause low milk yield, or fifty-fifty mastitis (inflammation of the udder).^[2] So-called "tingle voltage filters" may exist required in the electrical distribution system for a milking parlour.

Connecting the neutral to the equipment case provides some protection against faults, but may produce a unsafe voltage on the example if the neutral connectedness is broken.

Combined neutral and ground conductors are normally used in electricity supply companies' wiring and occasionally for fixed wiring in buildings and for some specialist applications where there is footling alternative, such every bit railways and trams. Since normal circuit currents in the neutral usher tin can lead to objectionable or unsafe differences between local earth potential and the neutral, and to protect against neutral breakages, special precautions such as frequent rodding down to globe (multiple ground rod connections), use of cables where the combined neutral and world completely surrounds the phase conductor(s), and thicker than normal equipotential bonding must be considered to ensure the arrangement is safe.

Stock-still appliances on three-wire circuits [edit]

In the U.s.a., the cases of some kitchen stoves (ranges, ovens), melt tops, clothes dryers and other specifically listed appliances were grounded through their neutral wires every bit a measure to conserve copper from copper cables during World War 2. This practice was removed from the NEC in the 1996 edition, but existing installations (called "old work") may notwithstanding allow the cases of such listed appliances to be connected to the neutral conductor for grounding. (Canada did not adopt this arrangement and instead during this time and into the present uses separate neutral and ground wires.)

This practice arose from the three-wire arrangement used to supply both 120 volt and 240 volt loads. Because these listed appliances often have components that use either 120, or both 120 and 240 volts, there is often some current on the neutral wire. This differs from the protective grounding wire, which merely carries electric current under fault conditions. Using the neutral usher for grounding the equipment enclosure was considered prophylactic since the devices were permanently wired to the supply then the neutral was unlikely to be broken without likewise breaking both supply conductors. Too, the unbalanced current due to lamps and small motors in the appliances was small compared to the rating of the conductors and therefore unlikely to cause a large voltage drop in the neutral conductor.

Portable appliances [edit]

In North American and European practice, small portable equipment connected by a string fix is permitted under certain weather condition to have merely two conductors in the zipper plug. A polarized plug tin be used to maintain the identity of the neutral conductor into the appliance merely neutral is never used as a chassis/example ground. The modest cords to lamps, etc., oftentimes have 1 or more molded ridges or embedded strings to identify the neutral conductor, or may be identified past colour. Portable appliances never use the neutral usher for case grounding, and ofttimes characteristic "double-insulated" construction.

In places where the design of the plug and socket cannot ensure that a organization 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 achieve full primary voltage with respect to the ground.

Technical equipment [edit]

In N American practice, equipment connected past a cord prepare must have three wires if supplied exclusively by 240 volts, or must take 4 wires (including neutral and ground), if supplied by 120/240 volts.

There are special provisions in the NEC for so-chosen technical equipment, mainly professional person grade audio and video equipment supplied by so-called "balanced" 120 volt circuits. The centre tap of a transformer is connected to ground, and the equipment is supplied by two line wires each 60 volts to basis (and 120 volts betwixt line conductors). The center tap is not distributed to the equipment and no neutral usher is used. These cases more often than not use a grounding usher which is separated from the safety grounding conductor specifically for the purposes of noise and "hum" reduction.

Some other specialized distribution system was formerly specified in patient intendance areas of hospitals. An isolated ability organization was furnished, from a special isolation transformer, with the intention of minimizing any leakage current that could pass through equipment directly continued to a patient (for instance, an electrocardiograph for monitoring the centre). The neutral of the circuit was not continued to ground. The leakage current was due to the distributed capacitance of the wiring and capacitance of the supply transformer. ^[3] Such distribution systems were monitored past permanently installed instruments to give an alarm when loftier leakage electric current was detected.

Shared neutral [edit]

A shared neutral is a connection in which a plurality of circuits use the aforementioned neutral connexion. This is too known as a common neutral, and the circuits and neutral together are sometimes referred to every bit an Edison circuit.

3-phase circuits [edit]

In a iii-stage excursion, a neutral is shared between all iii phases. Commonly the system neutral is connected to the star point on the feeding transformer. This is the reason that the secondary side of most three-phase distribution transformers is wye- or star-wound. Three-phase transformers and their associated neutrals are normally found in industrial distribution environments.

A system could be made entirely ungrounded. In this instance a fault between one phase and basis would not cause any meaning current. Usually the neutral is grounded (earthed) through a bail between the neutral bar and the earth bar. It is common on larger systems to monitor any current flowing through the neutral-to-globe link and use this equally the basis for neutral mistake protection.

The connection between neutral and earth allows whatsoever phase-to-earth fault to develop enough current period to "trip" the circuit overcurrent protection device. In some jurisdictions, calculations are required to ensure the fault loop impedance is low enough and then that fault current will trip the protection (In Australia, this is referred to in AS3000:2007 Fault loop impedance calculation). This may limit the length of a co-operative circuit.

In the case of two phases sharing one neutral and the tertiary phase is disconnected, the worst-case current describe is 1 side has aught load and the other has full load, or when both sides have full load. The latter example results in $Im\bending 0^{\circ }+Im\angle -120^{\circ }=Im\angle -60^{\circ }$ , $Im\angle 0^{\circ }+Im\angle 120^{\circ }=Im\angle 60^{\circ }$ or $Im\angle 120^{\circ }+Im\angle -120^{\circ }=Im\angle 180^{\circ }$ where $Im$ is the magnitude of the current. In other words the magnitude of the current in the neutral equals that of the other two wires.

In a 3-phase linear circuit with 3 identical resistive or reactive loads, the neutral carries no current. The neutral carries electric current if the loads on each stage are not identical. 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 stage conductors, it tin 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 ability supplies, frequently contains harmonics. Triplen harmonic currents (odd multiples of the tertiary harmonic) are additive, resulting in more current in the shared neutral conductor than in whatsoever of the phase conductors. In the absolute worst example, the electric current in the shared neutral conductor can be triple that in each phase conductor. Some jurisdictions prohibit the use of shared neutral conductors when feeding single-phase loads from a three-phase source; others require that the neutral conductor be substantially larger than the stage conductors. It is good practice to utilize iv-pole excursion breakers (equally opposed to the standard iii-pole) where the fourth pole is the neutral phase, and is hence protected confronting overcurrent on the neutral conductor.

Split phase [edit]

In split-phase wiring, for example a duplex receptacle in a Due north American kitchen, devices may exist connected with a cable that has three conductors, in addition to ground. The three conductors are usually coloured red, black, and white. The white serves as a common neutral, while the scarlet and black each feed, separately, the peak and lesser hot sides of the receptacle. Typically such receptacles are supplied from 2 circuit breakers in which the handles of two poles are tied together for a common trip. If ii big appliances are used at once, electric current passes through both and the neutral only carries the difference in electric current. The advantage is that only three wires are required to serve these loads, instead of 4. If one kitchen appliance overloads the circuit, the other side of the duplex receptacle will be shut off also. This is chosen a multiwire branch excursion. Common trip is required when the connected load uses more than one phase simultaneously. The common trip prevents overloading of the shared neutral if one device draws more than rated current.

Grounding problems [edit]

A footing connexion that is missing or of inadequate capacity may not provide the protective functions as intended during a fault in the connected equipment. Extra connections between footing and circuit neutral may result in circulating current in the ground path, stray electric current introduced in the globe or in a construction, and stray voltage.^{[ commendation needed ]} Extra footing connections on a neutral conductor may bypass the protection provided by a ground-fault circuit interrupter. Signal circuits that rely on a basis connection volition not function or volition have erratic function if the ground connection is missing.

See likewise [edit]

Appliance classes
Electrical bonding
Electrical wiring
Electrical wiring (Uk)
Electrical wiring (United States)
Earthing arrangements
Footing (electricity)

References [edit]

^ For instance, in N American practice an overhead service-archway cable has two insulated conductors which are wrapped effectually and supported by the bare neutral conductor
^ Thomas J. Divers, Simon Francis Peek (ed),Rebhun's diseases of dairy cattle, Elsevier Health Sciences, 2008, ISBN one-4160-3137-v pp. 389–390
^ Leslie A. Geddes Handbook of Electrical Hazards and Accidents, CRC Press, 1995 ISBN 0849394317, pp. 90-91