Distribution board
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Image:ElectricalPanel.jpg A distribution board (known in the United States as a (circuit) breaker panel, panelboard, or load center or for old ones, fuse box) is a mounting enclosure for multiple electrical circuit breakers. These are generally placed in two rows. Small single-phase boxes, with the breakers in just one row, are known as consumer units in Britain. Distribution boards are typically found in central locations inside buildings and often serve as the point at which electricity is distributed within a building. Circuit breakers can be used to manually de-energize electrical circuits when wiring is being serviced. North American breaker panels commonly have the live parts exposed when the enclosure is open. British distribution boards generally have live parts enclosed to IP20, even with the cover off.
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Breaker arrangement
Breakers are usually arranged in two columns. In a US-style board, breaker positions are numbered left-to-right, along each row from top to bottom. Wires are black and red (Rarely blue) for live, white for neutral and bare or green for ground.
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| Phase | Breakers | |
|---|---|---|
| X | 1 | 2 |
| Y | 3 | 4 |
| Z | 5 | 6 |
| X | 7 | 8 |
| Y | 9 | 10 |
| Z | 11 | 12 |
These breakers cycle through two or three phases, labelled as X, Y, and Z in the above diagram. This numbering system is universal across various competing manufacturers of breaker panels.
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. It remains to be seen how the new wiring colours recently introduced in the UK will affect this labelling.
| Phase | Breakers | |
|---|---|---|
| Red | R1 | R4 |
| Yellow | Y1 | Y4 |
| Blue | B1 | B4 |
| Red | R2 | R5 |
| Yellow | Y2 | Y5 |
| Blue | B2 | B5 |
| Red | R3 | R6 |
| Yellow | Y3 | Y6 |
| Blue | B3 | B6 |
In both labelling styles the reason for the alternating pattern of phases is to allow for common trip breakers to have one pole on each phase.
In North America it is common to wire large heating 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 and 208 V if the supply system is three phase. This practice is much less common in countries that use a higher line-neutral voltage. Large motors, air conditioners, subpanels, etc., are typically three-phase (where available). Therefore a three-pole breaker is needed which takes three slots in the breaker panel.
Inside a North American panel
Image:EEUU(GE)BreakerpanelInnards.jpg The picture to the right (Click to enlarge it) shows the interior of a standard residential service, North-American General Electric style breaker panel. The three power lines can be seen coming in at the top (One going to the neutral busbar to the left with all the white wires, the other two attached to the main breaker). Below it are the two rows of circut breakers with the circuit's hot wire leading off. A line can be seen directly existing the box and running to an electrical recepticle with something plugged into it.
Inside a UK distribution board
Image:UKDistributionBoard.JPGThis picture shows the interior of a typical 12-position UK distribution panel. The three incoming phase wires connect to the busbars via an isolator switch in the centre of the panel. The incoming neutral connects to the neutral busbar at the centre right of the board, which is in turn connected to the neutral busbar at the top left side of the board. The incoming earth wire connects to the earth busbar at the centre left side of the panel, which is in turn connected to the earth busbar at the top right of the board. The cover has been removed from the neutral bar at the right of the board; the neutral bar on the left side has its cover in place.
Down the left side of the phase busbars are two two-pole RCBOs 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 RCDOs in the picture are not connected across two phases, but have supply-side neutral connections exiting behind the phase busbars.
It is likely that the manufacturer produces 18- and 24-position versions of this panel using the same chassis which explains why there appears to be so much unused space.
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 rail for mounting and a standard cut-out shape as the positions of the busbar connections are not standardised.
It is commonly known in North America that Siemens and Cutler-Hammer panels and breakers of the type shown in the above and below picture illustrations are interchangeable one-inch wide breakers. Therefore, these two types of breaker panels have gained widespread acceptance as a "standard". The two panels shown (one Siemens, and the other Cutler Hammer) seem to fit GOULD Type QP, ITE type QT, Cutler Hammer Type BR, and Siemens breakers. The other standard commonly found in North America is the Square D "QO" standard (a 3/4 inch breaker). Both systems also allow the use of breakers which accommodate two individual circuit breaker functions within the width of a standard (1" or 3/4") case, but not all positions in all distribution boards may allow the use of such dual breakers.
Numerous older systems are still in use in older buildings and are still manufactured for these legacy applications, such as Zinsco and others.
Location
For reasons of aesthetics and security, circuit breaker panels are often placed in out-of-the-way closets, attics, garages, or basements, 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.
Larger buildings or facilities with high electric power 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, 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.
Distribution boards may be surface-mounted on a wall or may be sunk in to 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 in to the wall.
Mobile operation
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Sometimes it is desired to have a portable breaker panel, for example, for special events. In this case, a breaker panel is mounted to a board, together with various sockets. These are common in the movie industry. The American one pictured at the right has a cord with an L21-30 plug to supply power. Power leaves the board through four three-phase circuits: three 15 ampere 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 20A duplex receptacle shown at the upper left. The neon nightlights on the upper right triplex box are to show the phase sequence.