Distribution board
Encyclopedia
Fuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...
or circuit breaker
Circuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
for each circuit, in a common enclosure
Enclosure (electrical)
An electrical enclosure is a cabinet for electrical or electronic equipment to mount switches, knobs and displays and to prevent electrical shock to equipment users and protect the contents from the environment...
. Normally, a main switch
Switch
In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....
, and in recent boards, one or more Residual-current device
Residual-current device
A Residual Current Device is a generic term covering both RCCBs and RCBOs.A Residual-Current Circuit Breaker is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor...
s (RCD) or Residual Current Breakers with Overcurrent protection (RCBO), will also be incorporated.
Other names
Distribution boards are also referred to as a:- breaker panel
- circuit breaker panel
- consumer unitConsumer unitA consumer unit is a box of fuses or breakers, usually arranged in a single row. This is unlike a distribution board which has multiple rows of fuses or breakers and usually serves two or more locations, which may be split phase, two phase, two phases taken from three phase, or three phases.A...
, or CU - electrical panel
- fusebox
- fuseboard
- load centre/center
- panelboard
- power breaker
- service panel
- DB board (South Africa)
North American breaker panels
The circuit breakerCircuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
s are generally placed in two columns. Circuit breaker panelboards are always dead front, that is, the operator of the circuit breakers cannot contact live electrical parts. During servicing of the distribution board itself, though, when the cover has been removed and the cables are visible, North American breaker panelboards commonly have some live parts exposed.
Breaker arrangement
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Each row is fed from a different phase (A, B, and C below), to allow 2- or 3-pole common-trip breakers to have one pole on each phase. In North America, it is common to wire large permanently installed equipment line-to-line. This takes two slots in the panel (two-pole) and gives a voltage of 240V if the supply system is split phase
Split phase
A split-phase electricity distribution system is a 3-wire single-phase distribution system, commonly used in North America for single-family residential and light commercial applications. It is the AC equivalent of the original Edison 3-wire direct current system...
and 208 V if the supply system is three phase.
Inside a North American panel
breakerpanelinnards.jpg)
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
style breaker panel. The three power lines can be seen coming in at the top (One going to the neutral busbar
Busbar
In electrical power distribution, a bus bar is a strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus....
to the left with all the white wires, the other two attached to the main breaker). Below it are the two rows of circuit breakers with the circuit's hot wire leading off. A line can be seen directly exiting the box and running to a NEMA 5-15 electrical receptacle with a power cord
Power cord
A power cord, line cord, or mains cable is a cable that temporarily connects an appliance to the mains electricity supply via a wall socket or extension cord. The terms are generally used for cables using a power plug to connect to a single-phase alternating current power source at the local line...
tucked into it.
UK boards
In the UK, domestic and small commercial or public installations usually have single-phase supplies at 230V (nominal standard). The main distribution boards in these installations are called consumer unitConsumer unit
A consumer unit is a box of fuses or breakers, usually arranged in a single row. This is unlike a distribution board which has multiple rows of fuses or breakers and usually serves two or more locations, which may be split phase, two phase, two phases taken from three phase, or three phases.A...
s (CUs), though they may be known as fuse boxes; older consumer units used fuses
Fuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...
until the advent of mini-circuit breakers
Circuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
(MCBs).
A consumer unit normally has a single horizontal row of fuses or MCBs, though some older units grouped four fuses in a square arrangement. For two-rate supplies (standard/off-peak), a second CU may be added (stacked). Multiple CUs are also found in larger premises.
Larger commercial, public, and industrial installations generally use three-phase supplies, with distribution boards which have twin vertical rows of breakers. Larger installations will often use subsidiary distribution boards.
In both cases, modern boards handling supplies up to around 100 A (CUs) or 200 A (distribution boards) use circuit breakers and RCDs on DIN rail
DIN rail
A DIN rail is a metal rail of a standard type widely used for mounting circuit breakers and industrial control equipment inside equipment racks...
mountings. The main distribution board in an installation will also normally provide a main switch (known as an incomer) which switches the phase and neutral lines for the whole supply. (n.b., an incomer may be referred to, or sold as, an isolator
Isolator switch
In electrical engineering, a disconnector or isolator switch is used to make sure that an electrical circuit can be completely de-energised for service or maintenance. Such switches are often found in electrical distribution and industrial applications where machinery must have its source of...
, but this is problematic, as it will not necessarily be used as an isolator in the strict sense.)
For each phase, power is fed along a busbar
Busbar
In electrical power distribution, a bus bar is a strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus....
. In split-phase panels, separate busbars are fed directly from the incomer, which allows RCDs to be used to protect groups of circuits. Alternatively RCBOs may be used to provide both overcurrent and residual-current protection to single circuits.
Other devices, such as transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
s (e.g., for bell circuits) and contactors (relays; e.g., for large motor or heating loads) may also be used.
New British distribution boards generally have the live parts enclosed to IP20, even when the cover has been removed for servicing.
Modern CU
A typical new domestic CU used as a main panel may have from 6 to 24 ways for devices (some of which may occupy two ways), and will be split into two or more sections (e.g. a non-RCD section for alarms etc., an RCD-protected section for socket outlets, and an RCD-protected section for lighting and other built-in appliances). Secondary CUs used for outbuildings usually have 1 to 4 ways plus an RCD.Older CUs
Recent (pre-17th edition wiring regulations) CUs would not usually have RCD protected sections for anything other than socket outlets, though some older CUs used RCD Incomers. Before the 1990s RCDs (and split busbars) were not standard in CUs.Fuse Boxes usually use cartridge or rewirable fuses with no other protective device, and basic 4-ways boxes are very common. Some older boxes are made of brown-black bakelite, sometimes with a wooden base. Although their design is historic, these were standard equipment for new installs as recently as the 1980s, so they are very common. Fuseholders in these boxes may not provide protection from accidental contact with live terminals.
The popular 4-way fusebox usually has two lighting and two socket circuits, with heavy or sustained loads such as immersion heater and oven on a socket circuit. This arrangement is not recommended practice today, but it is common in existing installations. Larger boxes with more ways will have separate fuses for large loads such as immersion heater, oven and shower.
Circuit breaker retrofits
Some of these fuseboxes have had their fuseFuse
The word fuse has several meanings:* Fuse , a device used in electrical systems to protect against excessive current....
carriers replaced with plug-in miniature circuit breakers. These retrofit MCBs are typically rated at 3kA breaking capacity, but many homes or properties have prospective short circuit currents as high as 6kA. Fault currents of over 3kA are thus interrupted by the incomer fuse, should they ever occur, and the MCB would not survive.
Historic fuseboxes
A small number of pre-1950 fuseboxes are still in service. These should be treated with caution because exposed live parts are common on these boxes. The installations they supply will not meet modern standards for electrical safety. Another characteristic of very old installations is that there may be two fuses for each circuit; one on the liveLive wire (electricity)
The live wire in an AC electrical circuit refers to the wire which carries an oscillating voltage with respect to the earth...
and one on the neutral. In rare instances, old ring circuits may be encountered with no less than 4 15 A fuses per ring, one on each of L and N, and this duplicated for each of the 2 feeds for the ring.
Inside a UK distribution board
Busbar
In electrical power distribution, a bus bar is a strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus....
s, for neutral and earth. The incoming neutral connects to the lower busbar on the right side of the panel, which is in turn connected to the neutral busbar at the top left. The incoming earth wire connects to the lower busbar on the left side of the panel, which is in turn connected to the earth busbar at the top right. The cover has been removed from the lower-right neutral bar; the neutral bar on the left side has its cover in place.
Down the left side of the phase busbars are two two-pole RCBO
Residual-current device
A Residual Current Device is a generic term covering both RCCBs and RCBOs.A Residual-Current Circuit Breaker is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor...
s and two single-pole breakers, one unused. Down the right side of the busbars are a single-pole breaker, a two-pole RCBO and a three-pole breaker.
The two-pole RCBOs in the picture are not connected across two phases, but have supply-side neutral connections exiting behind the phase busbars.
The illustrated panel includes a great deal of unused space; it is likely that the manufacturer produces 18- and 24-position versions of this panel using the same chassis.
In a UK-style board, breaker positions are numbered top to bottom in the left hand column, then top to bottom in the right column. Each number is used to label one position on each phase, as below, and can be seen faintly in the photograph to the right. It remains to be seen how the new wiring colours
Electrical wiring (UK)
There are a number of specific national practices, habits and traditions associated with consumer mains wiring in the United Kingdom that differ significantly from other countries...
recently introduced in the UK will affect this labelling.
Manufacturer differences
Most of the time, the panel and the breakers inserted into it must both be from the same company. Each company has one or more "systems", or kinds of breaker panels, that only accept breakers of that type. In Europe this is still the case, despite the adoption of a standard DIN railDIN rail
A DIN rail is a metal rail of a standard type widely used for mounting circuit breakers and industrial control equipment inside equipment racks...
for mounting and a standard cut-out shape, as the positions of the busbar connections are not standardised.
Certain panels use seemingly interchangeable 1 inches (25.4 mm) breakers. However, a given manufacturer will often specify exactly what devices are permitted to be installed in their equipment. These assemblies have been tested and approved for use by a recognized authority. Replacing or adding equipment which "just happens to fit" can result in unexpected or even dangerous conditions. Such installations should not be done without first consulting knowledgeable sources, including manufacturers.
Location and designation
For reasons of aestheticsAesthetics
Aesthetics is a branch of philosophy dealing with the nature of beauty, art, and taste, and with the creation and appreciation of beauty. It is more scientifically defined as the study of sensory or sensori-emotional values, sometimes called judgments of sentiment and taste...
and security, circuit breaker panels are often placed in out-of-the-way closet
Closet
A closet is a small and enclosed space, a cabinet, or a cupboard in a house or building used for general storage or hanging clothes. A closet for food storage is usually referred to as a pantry...
s, attic
Attic
An attic is a space found directly below the pitched roof of a house or other building . Attic is generally the American/Canadian reference to it...
s, garages
Garage (house)
A residential garage is part of a home, or an associated building, designed or used for storing a vehicle or vehicles. In some places the term is used synonymously with "carport", though that term normally describes a structure that is not completely enclosed.- British residential garages:Those...
, or basement
Basement
__FORCETOC__A basement is one or more floors of a building that are either completely or partially below the ground floor. Basements are typically used as a utility space for a building where such items as the furnace, water heater, breaker panel or fuse box, car park, and air-conditioning system...
s, but sometimes they are also featured as part of the aesthetic elements of a building (as an art installation, for example) or where they can be easily accessed. However, current US building codes prohibit installing a panel in a bathroom (or similar room), in closets intended for clothing, or where there is insufficient space for a worker to access it. Specific situations, such as an installation outdoors, in a hazardous environment, or in other out-of-the-ordinary locations may require specialized equipment and more stringent installation practices.
Large buildings or facilities with higher electric power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...
demand may have multiple circuit breaker panels. In this case, the panels are often indicated by letters of the alphabet. One case is The Decon Gallery, a modern building in downtown Toronto
Toronto
Toronto is the provincial capital of Ontario and the largest city in Canada. It is located in Southern Ontario on the northwestern shore of Lake Ontario. A relatively modern city, Toronto's history dates back to the late-18th century, when its land was first purchased by the British monarchy from...
, which has 11 breaker panels designated A, B, C, D, and so on. A backstage outlet is therefore labeled C27. In many such buildings, each outlet is on its own circuit breaker, and the outlets are labelled in the above specified manner to facilitate easy location of which breaker to shut off for servicing, rewiring, or the like.
In even larger buildings, such as schools, hospitals and sports/entertainment venues it is not uncommon to have scores of panels, specially designated for each building depending on how the architects and electrical engineers subdivide the building. They are commonly designated as either three-phase
Three-phase electric power
Three-phase electric power is a common method of alternating-current electric power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by grids worldwide to transfer power. It is also used to power large motors and other heavy loads...
or single-phase
Single-phase electric power
In electrical engineering, single-phase electric power refers to the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors...
and normal power or emergency power. In these set-ups they may also be designated for their use, such as distribution panels for supplying other panels, lighting panels for lights, power panels for equipment and receptacles and special uses for whatever type of building they are used in. It is also not uncommon for these panels to be located throughout the building in electric closets serving a section of the building.
In a theatre a specialty panel called a dimmer
Dimmer
Dimmers are devices used to vary the brightness of a light. By decreasing or increasing the RMS voltage and, hence, the mean power to the lamp, it is possible to vary the intensity of the light output...
rack is used to feed stage lighting instruments. A US style dimmer rack has a 208Y/120 volt 3-phase feed. Instead of just circuit breakers, the rack has a solid state electronic dimmer with its own circuit breaker for each stage circuit. This is known as a dimmer-per-circuit arrangement. The dimmers are equally divided across the three incoming phases. In a 96 dimmer rack, there are 32 dimmers on phase A, 32 dimmers on phase B, and 32 on phase C to spread out the lighting load as equally as possible. In addition to the power feed from the supply transformer in the building, a control cable from the lighting desk carries information to the dimmers in a control protocol such as DMX-512. The information includes commands on levels, fade times, and which dimmers come up and go out during the lighting changes of the show (light cues).
Distribution boards may be surface-mounted on a wall or may be sunk into the wall. The former arrangement allows for easier alteration or addition to wiring at a later date, but the latter arrangement may look neater, particularly in a residential situation. The other problem with recessing a distribution board into a wall is that if the wall is solid a lot of brick or block may need to be removed - for this reason recessed boards are generally only fitted on new-build projects when the required space can be built into the wall.
Mobile operation
Ampere
The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...
circuits; and one 20 A circuit. The 15 A circuits each go to a triplex-box. The 20 A circuit goes to an L21-20 receptacle, and one leg of it goes to a 20 A duplex receptacle shown at the upper left. The neon night-lights on the upper right triplex box are to show the phase presence.
The use of a load center in this type of configuration is dangerous and violates UL and NEC rules for their use. When power distribution is required on movie sets, concert stages and theatrical venues it should be provided via products Listed "for portable power distribution."
See also
- Consumer unitConsumer unitA consumer unit is a box of fuses or breakers, usually arranged in a single row. This is unlike a distribution board which has multiple rows of fuses or breakers and usually serves two or more locations, which may be split phase, two phase, two phases taken from three phase, or three phases.A...
- Electric switchboardElectric switchboardAn electric switchboard is a device that directs electricity from one source to another. It is an assembly of panels, each of which contains switches that allow electricity to be redirected. The U.S...
- Electricity meterElectricity meterAn electricity meter or energy meter is a device that measures the amount of electric energy consumed by a residence, business, or an electrically powered device....
- Circuit Total LimitationCircuit Total LimitationCircuit total limitation is one of the present-day standards for electrical panels sold in the United States according to the National Electrical Code. The 1965 edition of the NEC, article 384-15 was the first reference to the circuit total limitation of panelboards...
- BusbarBusbarIn electrical power distribution, a bus bar is a strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus....
External links
- Open Source SVG Distribution Board, Electrical Panel - VitalBodies.net. The graphic is generic, nice for mapping out ones circuits, or as a starting point for drawing a more specific non-generic panel. Created in Inkscape.