Low voltage

In electrical engineering low voltage is a relative term, the definition varying by context. Different definitions are used in electric power transmission and distribution, and electrical safety codes define “low voltage” circuits that are exempt from the protection required at higher voltages. These definitions vary by country and specific codes or regulations.

Contents

IEC Definition[edit]

The International Electrotechnical Commission (IEC) defines supply system low voltage as voltage in the range 50 to 1000 V AC or 120 to 1500 V DC.

In electrical power systems low voltage most commonly refers to the mains voltages as used by domestic and light industrial and commercial consumers. “Low voltage” in this context still presents a risk of electric shock, but only a minor risk of electric arcs through the air.

UK[edit]

  • British Standard BS 7671:2008 defines supply system low voltage as:

50 to 1000 VAC or 120 to 1500 V ripple-free DC between conductors;
50 to 600 VAC or 120 to 900 V ripple-free DC between conductors and Earth.

USA[edit]

In electrical power distribution, the United States 2005 National Electrical Code (NEC) defines low (distribution system) voltage as 0 to 49 volts. Low distribution system voltage is covered by Article 725 of this code.

The NFPA standard 79 article 6.4.1.1 defines distribution protected extralow voltage (PELV) as nominal voltage of 30 Vrms or 60 VDC ripple free for dry locations and 6 Vrms or 15 VDC in all other cases.

UL standard 508A article 43 (Table 43.1) defines 0 to 20 V peak/ 5 A or 20.1 to 42.4 V peak/ 100 VA as Low-Voltage Limited Energy circuits.

See also[edit]

References[edit]

Further reading[edit]


Electrician

For other uses, see Electrician (disambiguation).

An electrician is a tradesman specializing in electrical wiring of buildings, transmission lines, stationary machines, and related equipment. Electricians may be employed in the installation of new electrical components or the maintenance and repair of existing electrical infrastructure.[1] Electricians may also specialize in wiring ships, airplanes, and other mobile platforms, as well as data and cable lines.

Contents

Terminology

Electricians were originally people who demonstrated or studied the principles of electricity, often electrostatic generators of one form or another.[2]

In the United States, electricians are divided into two primary categories: linemen, who work on electric utility company distribution systems at higher voltages, and wiremen, who work with the lower voltages utilized inside buildings. Wiremen are generally trained in one of five primary specialties: commercial, residential, light industrial, industrial, and low-voltage wiring, more commonly known as Voice-Data-Video, or VDV. Other sub-specialties such as control wiring and fire-alarm may be performed by specialists trained in the devices being installed, or by inside wiremen.

Electricians are trained to one of three levels: Apprentice, Journeyman, and Master Electrician. In the US and Canada, apprentices work and receive a reduced compensation while learning their trade. They generally take several hundred hours of classroom instruction and are contracted to follow apprenticeship standards for a period of between three and six years, during which time they are paid as a percentage of the Journeyman’s pay. Journeymen are electricians who have completed their Apprenticeship and who have been found by the local, State, or National licensing body to be competent in the electrical trade. Master Electricians have performed well in the trade for a period of time, often seven to ten years, and have passed an exam to demonstrate superior knowledge of the National Electrical Code, or NEC.

Service electricians are tasked to respond to requests for isolated repairs and upgrades. They have skills troubleshooting wiring problems, installing wiring in existing buildings, and making repairs. Construction electricians primarily focus on larger projects, such as installing all new electrical system for an entire building, or upgrading an entire floor of an office building as part of a remodeling process. Other specialty areas are marine electricians, research electricians and hospital electricians. “Electrician” is also used as the name of a role in stagecraft, where electricians are tasked primarily with hanging, focusing, and operating stage lighting. In this context, the Master Electrician is the show’s chief electrician. Although theater electricians routinely perform electrical work on stage lighting instruments and equipment, they are not part of the electrical trade and have a different set of skills and qualifications from the electricians that work on building wiring.

In the film industry and on a television crew the head electrician is referred to as a Gaffer.

Electrical contractors are businesses that employ electricians to design, install, and maintain electrical systems. Contractors are responsible for generating bids for new jobs, hiring tradespeople for the job, providing material to electricians in a timely manner, and communicating with architects, electrical and building engineers, and the customer to plan and complete the finished product.

Training and regulation of trade

Electrician installing new meter socket on the side of a house.

Many jurisdictions have regulatory restrictions concerning electrical work for safety reasons due to the many hazards of working with electricity. Such requirements may be testing, registration or licensing. Licensing requirements vary between jurisdictions.

Australia

An electrician’s license entitles the holder to carry out all types of electrical installation work in Australia without supervision. However, to contract, or offer to contract, to carry out electrical installation work, a licensed electrician must also be registered as an electrical contractor. Under Australian law, electrical work that involves fixed wiring is strictly regulated and must almost always be performed by a licensed electrician or electrical contractor.[3] A local electrician can handle a range of work including air conditioning, light fittings and installation, safety switches, smoke alarm installation, inspection and certification and testing and tagging of electrical appliances.

To provide data, structured cabling systems, home automation & theatre, LAN, WAN and VPN data solutions or phone points, an installer must be licensed as a Telecommunications Cable Provider under a scheme controlled by Australian Communications and Media Authority[4]

Electrical licensing in Australia is regulated by the individual states. In Western Australia, the Department of Commerce tracks licensee’s and allows the public to search for individually named/licensed Electricians.[5]

Currently in Victoria the apprenticeship last for four years, during three of those years the apprentice attends trade school in either a block release of one week each month or one day each week. At the end of the apprenticeship the apprentice is required to pass three examinations, one of which is theory based with the other two practically based. Upon successful completion of these exams, providing all other components of the apprenticeship are satisfactory, the apprentice is granted an A Class licence on application to Energy Safe Victoria (ESV).

An A Class electrician may perform work unsupervised but is unable to work for profit or gain without having the further qualifications necessary to become a Registered Electrical Contractor (REC) or being in the employment of a person holding REC status. However, some exemptions do exist.[6]

In most cases a certificate of electrical safety must be submitted to the relevant body after any electrical works are performed.

Safety equipment used and worn by electricians in Australia (including insulated rubber gloves and mats) needs to be tested regularly to ensure it is still protecting the worker. Because of the high risk involved in this trade, this testing needs performed regularly and regulations vary according to state. Industry best practice is the Queensland Electrical Safety Act 2002, and requires six-monthly testing.

Canada

A utility electrician/lineman does maintenance on a utility pole.

Training of electricians follows an apprenticeship model, taking four or five years to progress to fully qualified journeyman level.[7] Typical apprenticeship programs consists of 80-90% hands-on work under the supervision of journeymen and 10-20% classroom training.[8] Training and licensing of electricians is regulated by each province, however professional licenses are valid throughout Canada under Agreement on Internal Trade. An endorsement under the Red Seal Program provides additional competency assurance to industry standards.[9]
In order for individuals to become a licensed electricians, they need to have 9000 hours of practical, on the job training. They also need to attend school for 4 terms and pass a provincial exam. This training enables them to become journeyman electricians. Furthermore, in British Columbia, an individual can go a step beyond that and become a “FSR”, or field safety representative. This credential gives the ability to become a licensed electrical contractor and to pull permits. Notwithstanding this, some Canadian provinces only grant “permit pulling privileges” to current Master Electricians, that is, a journeyman who has been engaged in the industry for three (3) years AND has passed the Master’s examination (i.e. Alberta). The various levels of field safety representatives are A,B and C. The only difference between each class is that they are able to do increasingly higher voltage and current work.

United Kingdom

Competency standards in the UK are defined by the Sector Skills council Summit Skills. Qualifications certificated by awarding organisations such as City and Guilds and EAL are based on these National Occupational Standards. Once qualified and demonstrating the required level of competence an Electrician can register with the JIB (Joint industry Board) for an Electrotechnical Certification Scheme (ECS) card. Electrical competence is required at Level 3 to practice as an electrician in the UK. The electrical industry is one of the few that require a trade test to be achieved prior to being fully qualified. This is known as the AM2.

Electricians can demonstrate further competence by studying further qualifications in Design and Verification of Electrical Installations or in the Test and Inspection of Electrical Installations. These qualifications can be listed on the reverse of the JIB card.

The Electricity at Work Regulations are the statutory document that covers electrical installations. Further information is provided in the non-statutory document BS7671 – Requirements for Electrical Installations otherwise known as the Wiring Regulations currently (2013) in their 17th Edition. Installations that comply with BS7671 are deemed to have met the EAWR. Electrical Installation in domestic properties is governed by Part P of the Building Regulations and electricians have to register certain aspects of their work in domestic properties with the local building control authority.

With the exception of the work described in Part P of the Building Regulations there are no laws that prevent anyone from carrying out electrical work in the UK. A possible result of this is that during 2010/11 and in 2011/12 there were 3,822 domestic electrical fires in Great Britain, resulting in 14 deaths. Organisations such as the Electrical Safety Council are working hard to educate the public not to use electricians who are not fully qualified or competent and to check the ElectricSafe register to ensure an Electrician has been deemed competent.

United States

Although many electricians work for private contractors, many electricians get their start in the military.

The United States does not offer nationwide licensing and electrical licenses are issued by individual states. There are variations in licensing requirements, however, all states recognize three basic skill categories: level electricians. Journeyman electricians can work unsupervised provided that they work according to a master’s direction. Generally, states do not offer journeyman permits, and journeyman electricians and other apprentices can only work under permits issued to a master electrician. Apprentices may not work without direct supervision. [10]

Before electricians can work unsupervised, they are usually required to serve an apprenticeship lasting from 3 to 5 years under the general supervision of a Master Electrician and usually the direct supervision of a Journeyman Electrician.[10] Schooling in electrical theory and electrical building codes is required to complete the apprenticeship program. Many apprenticeship programs provide a salary to the apprentice during training. A Journeyman electrician is a classification of licensing granted to those who have met the experience requirements for on the job training (usually 4000 to 6000 hours) and classroom hours (about 144 hours). Requirements include completion of two to six years of apprenticeship training, and passing a licensing exam.[11]}.

Reciprocity

An electrician’s license is valid for work in the state where the license was issued. In addition, many states recognize licenses from other states, sometimes called interstate reciprocity participation, although there can be conditions imposed. For example, California reciprocates with Arizona, Nevada, and Utah on the condition that licenses are in good standing and have been held at the other state for five years.[12] Nevada reciprocates with Arizona, California, and Utah.[13] Maine reciprocates with New Hampshire and Vermont at the master level, and the state reciprocates with New Hampshire, North Dakota, Idaho, Oregon, Vermont, and Wyoming at the journeyman level.[14]

Tools

Electricians use a range of hand and power tools and instruments.

Two of the tools commonly used by electricians. The fish tape is used to pull conductors through conduits, or sometimes to pull conductors through hollow walls. The conduit bender is used to make accurate bends and offsets in electrical conduit.

Some of the more common tools are:

  • Conduit Bender: Bender used to bend various types of Electrical Conduit. These come in many variations including hand, electrical, and hydraulic powered.
  • Non-Contact Voltage Testers
  • Lineman’s Pliers: Heavy-duty pliers for general use in cutting, bending, crimping and pulling wire.
  • Diagonal Pliers (also known as side cutters or Dikes): Pliers consisting of cutting blades for use on smaller gauge wires, but sometimes also used as a gripping tool for removal of nails and staples.
  • Needle-Nose Pliers: Pliers with a long, tapered gripping nose of various size, with or without cutters, generally smaller and for finer work (including very small tools used in electronics wiring).
  • Wire Strippers: Plier-like tool available in many sizes and designs featuring special blades to cut and strip wire insulation while leaving the conductor wire intact and without nicks. Some wire strippers include cable strippers among their multiple functions, for removing the outer cable jacket.
  • Cable Cutters: Highly leveraged pliers for cutting larger cable.
  • Armored Cable Cutters: Commonly referred to by the trademark ‘Roto-Split’ , is a tool used to cut the metal sleeve on MC (Metal Clad) cable.
  • Multimeter: An instrument for electrical measurement with multiple functions. It is available as analog or digital display. Common features include: voltage, resistance, and current. Some models offer additional functions.
  • Unibit or Step-Bit: A metal-cutting drill bit with stepped-diameter cutting edges to enable convenient drilling holes in preset increments in stamped/rolled metal up to about 1.6mm (1/16 inch) thick. Commonly used to create custom knock-outs in a breaker panel or junction box.
  • Cord, Rope or Fish Tape. Used to manipulate cables and wires through cavities. The fishing tool is pushed, dropped, or shot into the installed raceway, stud-bay or joist-bay of a finished wall or in a floor or ceiling. Then the wire or cable is attached and pulled back.
  • Crimping Tools: Used to apply terminals or splices. These may be hand or hydraulic powered. Some hand tools have ratchets to insure proper pressure. Hydraulic units achieve cold welding, even for aluminum cable.
  • Insulation Resistance Tester: Commonly referred to as a Megger, these testers apply several hundred to several thousand volts to cables and equipment to determine the insulation resistance value.
  • Knockout Punch: For punching holes into boxes, panels, switchgear, etc. for inserting cable & pipe connectors.
  • GFI/GFCI Testers: Used to test the functionality of Ground-Fault Interrupting receptacles.
  • Voltmeter: An electrician’s tool used to measure electrical potential difference between two points in an electric circuit.
  • Other general-use tools include screwdrivers, hammers, reciprocating saws, drywall saws, flashlights, chisels, tongue and groove pliers (Commonly referred to as ‘Channellock®’ pliers, a famous manufacturer of this tool) and drills.

Safety

See also: Occupational safety and health

In addition to the workplace hazards generally faced by industrial workers, electricians are also particularly exposed to injury by electricity. An electrician may experience electric shock due to direct contact with energized circuit conductors or due to stray voltage caused by faults in a system. An electric arc exposes eyes and skin to hazardous amounts of heat and light. Faulty switchgear may cause an arc flash incident with a resultant blast. Electricians are trained to work safely and take many measures to minimize the danger of injury. Lockout and tagout procedures are used to make sure that circuits are proven to be de-energized before work is done. Limits of approach to energized equipment protect against arc flash exposure; specially designed flash-resistant clothing provides additional protection; grounding (earthing) clamps and chains are used on line conductors to provide a visible assurance that a conductor is de-energized. Personal protective equipment provides electrical insulation as well as protection from mechanical impact; gloves have insulating rubber liners, and work boots and hard hats are specially rated to provide protection from shock. If a system cannot be de-energized, insulated tools are used; even high-voltage transmission lines can be repaired while energized, when necessary.[15]

Electrical workers, which includes electricians, accounted for 34% of total electrocutions of construction trades workers in the United States between 1992–2003.[16]

Working conditions

Working conditions for electricians vary by specialization. Generally an electrician’s work is physically demanding such as climbing ladders and lifting tools and supplies. Occasionally an electrician must work in a cramped space or on scaffolding, and may frequently be bending, squatting or kneeling, to make connections in awkward locations. Construction electricians may spend much of their days in outdoor or semi-outdoor loud and dirty work sites. Industrial electricians may be exposed to the heat, dust, and noise of an industrial plant. Power systems electricians may be called to work in all kinds of adverse weather to make emergency repairs.

Trade organizations

Some electricians are union members and work under their union’s policies.

Australia

Electricians can choose to be represented by the Electrical Trade Union (ETU). Electrical Contractors can be represented by the National Electrical & Communications Association or Master Electricians Australia.

North America

Some electricians are union members. Some examples of electricians’ unions include the International Brotherhood of Electrical Workers, Canadian Union of Public Employees, and the International Association of Machinists and Aerospace Workers.
The International Brotherhood of Electrical Workers provides its own apprenticeships through its National Joint Apprenticeship and Training Committee and the National Electrical Contractors Association. Many merit shop training and apprenticeship programs also exist, including those offered by such as trade associations as Associated Builders and Contractors and Independent Electrical Contractors. These organizations provide comprehensive training, in accordance with U.S. Department of Labor regulations.

United Kingdom/Ireland

In the United Kingdom, electricians are represented by several unions including Unite the Union

In the Republic of Ireland there are two self-regulation/self certification bodies RECI Register of Electrical Contractors of Ireland and ECSSA.

Auto electrician

An auto electrician is a tradesman specializing in electrical wiring of motor vehicles. Auto electricians may be employed in the installation of new electrical components or the maintenance and repair of existing electrical components. Auto electricians specialize in cars and commercial vehicles. The auto electrical trade is generally more difficult than the electrical trade due to the confined spaces, engineering complexity of modern automotive electrical systems, and working conditions (often roadside breakdowns or on construction sites, mines, quarries to repair machinery etc.) Also the presence of high-current DC electricity makes injury from burns and arc-flash injury possible.

See also

References

  • ^ Roger Jones (2004). Electrician. Trotman Publishing. ISBN 0-85660-997-8..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output .citation q{quotes:”””””””‘””‘”}.mw-parser-output .id-lock-free a,.mw-parser-output .citation .cs1-lock-free a{background:url(“//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png”)no-repeat;background-position:right .1em center}.mw-parser-output .id-lock-limited a,.mw-parser-output .id-lock-registration a,.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a{background:url(“//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png”)no-repeat;background-position:right .1em center}.mw-parser-output .id-lock-subscription a,.mw-parser-output .citation .cs1-lock-subscription a{background:url(“//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png”)no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-ws-icon a{background:url(“//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Wikisource-logo.svg/12px-Wikisource-logo.svg.png”)no-repeat;background-position:right .1em center}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-maint{display:none;color:#33aa33;margin-left:0.3em}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
  • ^ Shock and Awe: The Story of ElectricityJim Al-Khalili
  • ^ Tester, Ross (2008-06-05). “DIY Electrical Work: Are Aussies DUMBER than Kiwis?”. Silicon Chip Online. Retrieved 2012-07-20.
  • ^
    “Telecommunications Cabling Provider Rules 2014”. Australian Government. Retrieved 2018-02-23.
  • ^ Protection, corporateName: Department of Consumer and Employment; Division, corporateName: Consumer Protection; Hoskins, personalName: David. “Consumer Protection – Energy Safety”. bizline.commerce.wa.gov.au. Archived from the original on 2011-04-06. Retrieved 28 March 2018.
  • ^ “Archived copy”. Archived from the original on 2010-01-24. Retrieved 2010-02-15.CS1 maint: archived copy as title (link)
  • ^ http://www.tableauellis.ca/tr.1d.2ch.1rt@-eng.jsp?&tid=51[permanent dead link]
  • ^ http://www.hrsdc.gc.ca/eng/jobs/trades/index.shtml Government of Canada
  • ^ <Red Seal Program “Archived copy”. Archived from the original on 2010-11-02. Retrieved 2010-10-28.CS1 maint: archived copy as title (link)
  • ^ a b Hering, Bob. “Differences Between a Journeyman & a Master Electrician”. Houston Chronicle. Demand Media. Retrieved 10 April 2013.
  • ^ “What Is a Journeyman Electrician?”. Retrieved 2017-01-29.
  • ^ http://www.cslb.ca.gov/applicants/Reciprocity/ReciprocityRequirements.asp CSLB CA
  • ^ http://www.nvcontractorsboard.com/reciprocity.html Archived 2013-03-10 at the Wayback Machine State of NV
  • ^ http://www.maine.gov/pfr/professionallicensing/professions/electricians/pdf/elecreciprocity.pdf State of ME
  • ^ John Cadick et al, Electrical Safety Handbook Third Edition, Mc Graw Hill 2005, ISBN 0-07-145772-0
  • ^ http://www.elcosh.org/en/document/557/d000539/why-are-so-many-construction-workers-being-electrocuted%253F.html Michael McCann, Why Are So Many Construction Workers Being Electrocuted?, retrieved 2010 July 27
  • External links


    Steel wire armoured cable

    Steel wire armoured cable, commonly abbreviated as SWA, is a hard-wearing power cable designed for the supply of mains electricity. It is one of a number of armoured electrical cables – which include 11 kV Cable and 33 kV Cable – and is found in underground systems, power networks and cable ducting.[1]

    Contents

    Construction[edit]

    Example of steel wire armoured cables in a UK installation. Blue sheathed cable is normally instrumentation signal, black is power

    The typical construction of an SWA cable can be broken down as follows:

    • Conductor: consists of plain stranded copper (cables are classified to indicate the degree of flexibility. Class 2 refers to rigid stranded copper conductors as stipulated by British Standard BS EN 60228:2005[2])
    • Insulation: Cross-linked polyethylene (XLPE) is used in a number of power cables because it has good water resistance and excellent electrical properties. Insulation in cables ensures that conductors and other metal substances do not come into contact with each other.[3]
    • Bedding: Polyvinyl chloride (PVC) bedding is used to provide a protective boundary between inner and outer layers of the cable.
    • Armour: Steel wire armour provides mechanical protection, which means the cable can withstand higher stresses, be buried directly and used in external or underground projects.[4] The armouring is normally connected to earth and can sometimes be used as the circuit protective conductor (“earth wire”) for the equipment supplied by cable.
    • Sheath: a black PVC sheath holds all components of the cable together and provides additional protection from external stresses.

    The PVC version of SWA cable,[5] described above, meets the requirements of both British Standard BS 5467 and International Electrotechnical Commission standard IEC 60502.[6] It is known as SWA BS 5467 Cable and it has a voltage rating of 600/1000 V.[7]

    SWA cable can be referred to more generally as mains cable, armoured cable, power cable and booklet armoured cable. The name power cable, however, applies to a wide range of cables including 6381Y, NYCY, NYY-J and 6491X Cable.

    Aluminium wire armoured cable[edit]

    Steel wire armour is only used on multicore versions of the cable. A multicore cable, as the name suggests, is one where there are a number of different cores. When cable has only one core, aluminium wire armour (AWA) is used instead of steel wire. This is because the aluminium is non-magnetic. A magnetic field is produced by the current in a single core cable. This would induce an electric current in the steel wire, which could cause overheating.

    Use of armour for earthing[edit]

    cable with light armouring

    The use of the armour as the means of providing earthing to the equipment supplied by the cable (a function technically known as the circuit protective conductor or CPC) is a matter of debate within the electrical installation industry. It is sometimes the case that an additional core within the cable is specified as the CPC (for instance, instead of using a two core cable for line and neutral and the armouring as the CPC, a three core cable is used) or an external earth wire is run alongside the cable to serve as the CPC. Primary concerns are the relative conductivity of the armouring compared to the cores (which reduces as the cable size increases) and reliability issues. Recent articles by authoritative sources have analysed the practice in detail and concluded that, for the majority of situations, the armouring is adequate to serve as the CPC under UK wiring regulations.[8][9]

    SWA BS 6724 cable[edit]

    The construction of an SWA cable depends on the intended use. When the power cable needs to be installed in a public area, for example, a Low Smoke Zero Halogen (LSZH) equivalent, called SWA BS 6724 Cable must be used. After the King’s Cross fire in London in 1987 it became mandatory to use LSZH sheathing on all London Underground cables – a number of the fatalities were due to toxic gas and smoke inhalation. As a result, LSZH cables are now recommended for use in highly populated enclosed public areas. This is because they emit non-toxic levels of Halogen and low levels of smoke when exposed to fire. SWA Cable BS 6724 – which meets the requirements of British standard BS 6724 – has LSZH bedding and a black LSZH sheath.

    See also[edit]

    References[edit]

  • ^ Christopher Shelton (2004). Electrical Installations. Nelson Thornes. pp. 99–. ISBN 978-0-7487-7979-6..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output .citation q{quotes:”””””””‘””‘”}.mw-parser-output .id-lock-free a,.mw-parser-output .citation .cs1-lock-free a{background:url(“//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png”)no-repeat;background-position:right .1em center}.mw-parser-output .id-lock-limited a,.mw-parser-output .id-lock-registration a,.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a{background:url(“//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png”)no-repeat;background-position:right .1em center}.mw-parser-output .id-lock-subscription a,.mw-parser-output .citation .cs1-lock-subscription a{background:url(“//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png”)no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-ws-icon a{background:url(“//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Wikisource-logo.svg/12px-Wikisource-logo.svg.png”)no-repeat;background-position:right .1em center}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-maint{display:none;color:#33aa33;margin-left:0.3em}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
  • ^ British Standard BS EN 60228:2005. bsi-global.com
  • ^ A Closer Look At Cable: The Cable and Table Handbook. Draka. 2008.
  • ^ BS 5467 SWA Cable PVC
  • ^ John Whitfield (1995). Electrical Craft Principles. IET. pp. 253–. ISBN 978-0-85296-811-6.
  • ^ IEC 60502-1 Standard. iec.ch (2004)
  • ^ Trevor Marks (2002) Handbook on BS7671: The IEE Wiring Regulations – A Handbook of Compliance. Radikal Phase Publishing House Limited. ISBN 1904126022. p. 358
  • ^ The Use Of The Armour Of Steel Wire Armoured Cables As A Protective Conductor. gadsolutions.biz
  • ^ Darrell Locke (2008) Electrical Research Association Report (ERA) report on armoured cables with external CPCs – Appendix 16 in Guide to the Wiring Regulations:17th Edition IEE Wiring Regulations (BS 7671:2008). Wiley. ISBN 978-0-470-51685-0

  • Ring circuit

    This article is about a mains power configuration. For circuits where the components are connected in a ring, see ring modulation and phase-locked loop.

    In electricity supply design, a ring final circuit or ring circuit (often incorrectly called a ring main, a term used historically[1], or informally a ring) is an electrical wiring technique developed and primarily used in the United Kingdom. This design enables the use of smaller-diameter wire than would be used in a radial circuit of equivalent total current. The reduced diameter conductors in the flexible cords connecting an appliance to the plug intended for use with sockets on a ring circuit are individually protected by a fuse in the plug. Its advantages over radial circuits are therefore reduced quantity of copper used, and greater flexibility of appliances and equipment that can be connected.

    Ideally, the ring circuit acts like two radial circuits proceeding in opposite directions around the ring, the dividing point between them dependent on the distribution of load in the ring. If the load is evenly split across the two directions, the current in each direction is half of the total, allowing the use of wire with half the total current-carrying capacity. In practice, the load does not always split evenly, so thicker wire is used.

    Contents

    Description[edit]

    Diagram of a possible configuration of ring final circuit. Consumer unit (fuse box) is at bottom left.

    The ring starts at the consumer unit (also known as fuse box, distribution board, or breaker box), visits each socket in turn, and then returns to the consumer unit. The ring is fed from a fuse or circuit breaker in the consumer unit.

    Ring circuits are commonly used in British wiring with socket-outlets taking fused plugs to BS 1363. Because the breaker rating is much higher than that of any one socket outlet, the system can only be used with fused plugs or fused appliance outlets. They are generally wired with 2.5 mm2 cable and protected by a 30 A fuse, an older 30 A circuit breaker, or a European harmonised 32 A circuit breaker. Sometimes 4 mm2 cable is used if very long cable runs (to help reduce voltage drop) or derating factors such as very thick thermal insulation are involved. 1.5 mm2 mineral-insulated copper-clad cable (known as pyro) may also be used (as mineral insulated cable can withstand heat more effectively than normal PVC) though more care must be taken with regard to voltage drop on longer runs. The protection devices for the fixed wiring need to be rated higher than would protect flexible appliance cords, so BS 1363 requires that all plugs and connection units incorporate fuses appropriate to the appliance cord.

    History and use[edit]

    The ring circuit and the associated BS 1363 plug and socket system were developed in Britain during 1942–1947.[2] They are commonly used in the United Kingdom and to a lesser extent in the Republic of Ireland. They are also found in the United Arab Emirates, Singapore, Hong Kong, Beijing, Indonesia and many places where the UK had a strong influence, including for example Cyprus and Uganda.

    Pre-World War II practice was to use various sizes of plugs and sockets to suit the current requirement of the appliance, and these were connected to suitably fused radial circuits, the ratings of those fuses were appropriate to protect both the fixed wiring and the flexible cord attached to the plug.

    The Electrical Installations Committee which was convened in 1942 as part of the Post War Building Studies programme determined, amongst other things, that the ring final circuit offered a more efficient and lower cost system which would safely support a greater number of sockets.[3] The scheme was specified to use 13 A socket-outlets and fused plugs; several designs for the plugs and sockets were considered. The design chosen as the British Standard was the flat pin system now known as BS 1363. Other designs of 13 A fused plugs and socket-outlets, notably the Wylex and Dorman & Smith systems, which did not conform to the chosen standard, were used into the 1950s, but by the 1960s BS 1363 had become the single standard for new installations.

    There is a common misperception that the ring circuit was devised to combat the post-war copper shortage, but this is not supported by the textual record.

    The ring circuit is still the most common mains wiring configuration in the UK, although both 20 A and 30 A radial circuits are also permitted by the Wiring Regulations, with a recommendation based on the floor area served (20 A for area up to 25 m2, 30 A for up to 100 m2.).

    Installation rules[edit]

    Rules for ring circuits provide that the cable rating must be no less than two thirds of the rating of the protective device. This means that the risk of sustained overloading of the cable can be considered minimal. In practice, however, it is extremely uncommon to encounter a ring with a protective device other than a 30 A fuse, 30 A breaker, or 32 A breaker, and a cable size other than those mentioned above. Because the BS 1363 plug contains a fuse not exceeding 13A, the load at any one point on the ring is limited.

    The IET Wiring Regulations (BS 7671) permit an unlimited number of 13A socket outlets (at any point unfused single or double, or any number fused) to be installed on a ring circuit, provided that the floor area served does not exceed 100 m2. In practice, most small and medium houses have one ring circuit per storey, with larger premises having more.

    An installation designer may determine if additional circuits are required for areas of high demand. For example, it is common practice to put kitchens on their own ring circuit or sometimes a ring circuit shared with a utility room to avoid putting a heavy load at one point on the main downstairs ring circuit. Since any load on a ring is fed by the ring conductors on either side of it, it is desirable to avoid a concentrated load placed very near the feed, since the shorter conductors will have less impedance and carry a disproportionate share of the load.

    Unfused spurs from a ring wired in the same cable as the ring are allowed to run one socket (single or double) or one fused connection unit (FCU). Before 1970 the use of two single sockets on one spur was allowed, but has since been disallowed because of their conversion to double sockets. Spurs may either start from a socket or be joined to the ring cable with a junction box or other approved method of joining cables. BS 1363 compliant triple and larger sockets are always fused at 13A and therefore can also be placed on a spur. Since 1970 it is permitted to have more spurs than sockets on the ring, but it is considered poor practice by many electricians to have too many unfused spurs in a new installation (some think they are bad practice in all cases).

    Where loads other than BS 1363 sockets are connected to a ring circuit or it is desired to place more than one socket for low power equipment on a spur, a BS 1363 fused connection unit (FCU) is used. In the case of fixed appliances this will be a switched fused connection unit (SFCU) to provide a point of isolation for the appliance, but in other cases such as feeding multiple lighting points (putting lighting on a ring though is generally considered bad practice in new installation but is often done when adding lights to an existing property) or multiple sockets, an unswitched one is often preferable.

    Fixed appliances with a power rating of 3 kW or more (for example, water heaters and some electric cookers) or with a non-trivial power demand for long periods (for example, immersion heaters) may be connected to a ring circuit, but it is strongly recommended that instead they are connected to their own dedicated circuit. However, there are plenty of older installations with such loads on a ring circuit.

    Criticism[edit]

    The ring final circuit concept has been criticized in a number of ways compared to radials, and some of these concerns could explain the lack of widespread adoption outside the United Kingdom.

    Fault conditions are not apparent when in use[edit]

    Ring circuits may continue to operate without the user being aware of any problem if there are certain types of fault condition or installation errors. This gives both robustness against failure and a potential for danger [4]

    Safety tests are complex[edit]

    At least one author claims that testing ring circuits may take 5–6 times longer than testing radial circuits.[6] The installation tests required for the safe operation of a ring circuit are more time consuming than those for a radial circuit, and DIY installers or electricians qualified in other countries may not be familiar with them.

    Load Balance required[edit]

    Regulation 433-02-04 of BS 7671 requires that the installed load must be distributed around the ring such that no part of the cable exceeds its rated capacity. In some cases this requirement is difficult to guarantee, and may be largely ignored in practice, as loads are often co-located (e.g., washing machine, tumble dryer, dish washer all next to kitchen sink) at a point not necessarily near the centre of the ring.[6] However, the fact that the cable rating is 67% that of the circuit breaker, not 50%, means that a ring has to be significantly out of balance to cause a problem.

    In a ring circuit, if any poor joint causes a high resistance on one branch of the ring, current will be unevenly distributed, possibly overloading the remaining conductor of the ring.

    Can cause electromagnetic interference[edit]

    Ring circuits can occasionally generate unwanted magnetic fields.[citation needed] In a radial circuit, the current flowing in the circuit must return through (almost exactly) the same physical path through which it came, especially if the line and neutral conductors are kept in close proximity of each other and form a twisted pair. This prevents the circuit forming a large magnetic coil (loop antenna), which would otherwise induce a magnetic field at the AC frequency (50 or 60 Hz).

    Advantages[edit]

    Proponents of the ring circuit point out that, when correctly installed, there are also a number of advantages to be considered.

    Area served[edit]

    For rooms that are square or circular, a ring circuit can deliver more power per unit of floor area for a given cable size than a simple radial circuit, and the source impedance and therefore voltage drop to the furthest point is lower. Alternatively, to deliver the same power to the same building with radial circuits would require more final circuits or a heavier cable.

    High integrity earthing[edit]

    As all fittings on the ring are earthed from both sides, two independent faults are needed to create an ‘off earth’ fault

    Continuous Continuity verification from any point[edit]

    The continuity of each conductor right round all the points on the ring can be
    ooo verified from any point, and if this needs to be done as part of live installation monitoring, it can be verified by current clamp injection with the system energised.

    See also[edit]

    References[edit]

  • ^ “How To Use Your Wylex Plugs & Sockets” (PDF). Wylex. Retrieved 3 December 2019..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output .citation q{quotes:”””””””‘””‘”}.mw-parser-output .id-lock-free a,.mw-parser-output .citation .cs1-lock-free a{background:url(“//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png”)no-repeat;background-position:right .1em center}.mw-parser-output .id-lock-limited a,.mw-parser-output .id-lock-registration a,.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a{background:url(“//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png”)no-repeat;background-position:right .1em center}.mw-parser-output .id-lock-subscription a,.mw-parser-output .citation .cs1-lock-subscription a{background:url(“//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png”)no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-ws-icon a{background:url(“//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Wikisource-logo.svg/12px-Wikisource-logo.svg.png”)no-repeat;background-position:right .1em center}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-maint{display:none;color:#33aa33;margin-left:0.3em}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
  • ^ Malcolm Mullins: The origin of the BS 1363 plug and socket outlet system. IEE Wiring Matters, Spring 2006.
  • ^ D.W.M. Latimer: History of the BS 1363and the ring circuit. Presentation papers from a public meeting to discuss the issue of ring circuits, IET, London, October 2007 (PDF in ZIP)
  • ^ Roger Lovegrovep://www.theiet.org/resources/wiring-regulations/ringcir.cfm?type=zip Presentation papers from a public meeting to discuss the issue of ring circuits], IET, London, October 2007 (PDF in ZIP)
  • ^ P Knowles: Ring main lining. EMC, February 2007
  • ^ a b Roger Lovegrove: Ring circuits – the disadvantages. Presentation papers from a public meeting to discuss the issue of ring circuits, IET, London, October 2007 (PDF in ZIP)
  • External links[edit]


    National Inspection Council for Electrical Installation Contracting

    The National Inspection Council for Electrical Installation Contracting (NICEIC) is one of several organisations which regulates the training and work of electrical enterprises in the UK. The NICEIC is one of several providers given Government approval to offer Competent Person Schemes to oversee electrical work within the electrical industry.

    Certsure LLP (which is owned by Electrical Safety First, a registered charity, and the Electrical Contractors’ Association (ECA), the electrotechnical industry trade body) trades under the certification brands NICEIC and ELECSA.

    Contents

    History[edit]

    From 1923, an earlier organisation, the National Register of Electrical Installation Contractors, kept a register of approved electricians. It was incorporated on 10 August 1956, and since 1 October 2005, it has been registered as The Electrical Safety Council.

    Regulation[edit]

    Electrical contractors register with the organisation to become approved contractors, meeting the NICEIC’s specification of training. If work undertaken by the approved contractor is not up-to-standard, the NICEIC will correct it if necessary. Work is checked by 54 local Area Engineers. Many local authorities only give work to NICEIC-approved electricians.

    Most electrical items in domestic wiring are controlled from the consumer unit with its residual-current device (RCD), which since 2001 has to be installed. Homes are wired in a ring circuit.

    To be an approved contractor, the electrician must:

    • Ensure work is carried out to the current edition of BS 7671; the IET Wiring Regulations
    • Ensure certification is issued on completion of installation work, as directed by BS 7671
    • Have up-to-date copies of BS 7671
    • Have competence with test instruments as outlined by Part 6 (“Inspection and Testing”) of BS 7671; the IET Wiring Regulations
    • Have public liability insurance of at least £2m.

    See also[edit]

    External links[edit]

    Video clips[edit]


    IEC 60364

    IEC 60364 Electrical Installations for Buildings is the International Electrotechnical Commission‘s international standard on electrical installations of buildings. This standard is an attempt to harmonize national wiring standards in an IEC standard and is published in the European Union by CENELEC as “HD 60364”. The latest versions of many European wiring regulations (e.g., BS 7671 in the UK) follow the section structure of IEC 60364 very closely, but contain additional language to cater for historic national practice and to simplify field use and determination of compliance by electrical tradesmen and inspectors. National codes and site guides are meant to attain the common objectives of IEC 60364, and provide rules in a form that allows for guidance of persons installing and inspecting electrical systems.

    The standard has several parts:

    • Part 1: Fundamental principles, assessment of general characteristics, definitions
    • Part 4: Protection for safety
    • Part 5: Selection and erection of electrical equipment
      • Section 51: Common rules
      • Section 52: Wiring systems
      • Section 53: Isolation, switching and control
      • Section 54: Earthing arrangements, protective conductors and protective bonding conductors
      • Section 55: Other equipment (Note: Some national standards provide an individual document for each chapter of this section, i.e. 551 Low-voltage generating sets, 557 Auxiliary circuits, 559 Luminaires and lighting installations)
      • Section 56: Safety services
    • Part 6: Verification
    • Part 7: Requirements for special installations or locations
      • Section 701: Electrical installations in bathrooms
      • Section 702: Swimming pools and other basins
      • Section 703: Rooms and cabins containing sauna heaters
      • Section 704: Construction and demolition site installations
      • Section 705: Electrical installations of agricultural and horticultural premises
      • Section 706: Restrictive conductive locations
      • Section 708: Electrical installations in caravan parks and caravans
      • Section 709: Marinas and pleasure craft
      • Section 710: Medical locations
      • Section 712: Solar photovoltaic (PV) power supply systems
      • Section 713: Furniture
      • Section 714: External lighting
      • Section 715: Extra-low-voltage lighting installations
      • Section 717: Mobile or transportable units
      • Section 718: Communal facilities and workplaces
      • Section 721: Electrical installations in caravans and motor caravans
      • Section 722: Supplies for Electric Vehicles
      • Section 729: Operating or maintenance gangways
      • Section 740: Temporary electrical installations for structures, amusement devices and booths at fairgrounds, amusement parks and circuses
      • Section 753: Heating cables and embedded heating systems

    See also[edit]

    External links[edit]