A neutral wire is a conductor within an alternating current (AC) electrical distribution system which is intended to carry current and is also intended to be connected to earth (UK and EU) or ground (USA).[1] (The terms "earth" and "ground" herein refer to specific points or conductors within the electrical system and not necessarily to actual soil.)
Contents |
Difference from "phase" wires
This is contrasted by "phase", "live" or "hot" wires, which are also intended to carry electric current in a circuit, but are not earthed or grounded. Because of this difference, two or three "phase", "live" or "hot" wires can be connected to utilization equipment to deliver power within a circuit, but a "neutral" wire must be connected to utilization equipment along with at least one "phase", "live" or "hot" wire to form a circuit. All neutral wires of the same electrical system should have the same electrical potential, because they are all connected together through the system earth or ground -- therefore two neutral wires alone should have no potential difference (or voltage) between them. Theoretically, if the power circuits of the electrical distribution system are perfectly "balanced", this would result in zero electrical current on the neutral conductor, because of electrical phase vectors effectively cancelling each other. However, this is never actually the case, and for safety, any neutral conductor should always be regarded as effectively "live" or "hot" with current during operation.
Difference from "earth" or "ground" wires
While a neutral wire is always "grounded", it should not be confused with the electrical system's "equipment grounding conductor", which is not intended to carry any electric current during normal operation, but serves to do so in the event of a "fault", which is the unintentional imposition of current, such as during a "short circuit" or "ground fault". The electrical system's "equipment grounding conductors" (which are coloured green in the USA or green with a yellow stripe in the UK and EU), not its grounded conductors (or neutrals) serve to safely (and only momentarily) return unintentionally imposed current, such as during a fault condition, so that fuses or circuit breakers may interrupt the flow of current to maintain safety for personnel, utilization equipment, the electrical distribution system, and any nearby combustible contents or materials of a structure.
Circuitry
Neutral wires are usually connected together at a neutral bus (bar) within panelboards or switchboards, and are "bonded" to the electrical system's grounding or earthing system at either the electrical service entrance, or at transformers within the system. For small electrical installations such as residences with single phase service, the neutral point of the system is at the center-tap on the secondary side of the service transformer. For larger electrical installations, such as commercial, institutional, or industrial customers 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 result in no neutral point, and no neutral conductors.
Wiring colours
The insulation of a neutral wire is coloured blue in the UK and EU, but white or grey in the USA. For large diameter wires or "mains", the insulation of neutral conductors may actually be coloured black, as are also the phase or hot conductors, but are distinctively designated by applying coloured tape -- again blue in the UK and EU, and white or grey in the USA.
See also
References
- ^ Article 100 - Definitions, NFPA 70 National Electrical Code, 2005 Edition, International Electrical Code Series.
