Editing Distribution board (section)

==North America==

North American distribution boards are generally housed in [[sheet metal]] enclosures, with the [[circuit breaker]]s positioned in two columns operable from the front. Some panelboards are provided with a door covering the breaker switch handles, but all are constructed with a ''dead front''; that is to say the front of the enclosure (whether it has a door or not) prevents the operator of the circuit breakers from contacting live electrical parts within. [[Busbar]]s carry the current from incoming line (''hot'') conductors to the breakers, which are secured to the bus with either a ''bolt-on'' connection (using a threaded screw) or a ''plug-in'' connection using a retaining clip. ''Panelboards'' are more common in commercial and industrial applications and employ bolt-on breakers. Residential and light commercial panels are generally referred to as ''load centers'' and employ plug-in breakers. The neutral conductors are secured to a neutral bus using [[screw terminal]]s. The branch circuit [[electrical bonding|bonding]] conductors are secured to a terminal block attached directly to the panelboard enclosure, which is itself [[ground (electricity)|grounded]].

During servicing of the distribution board, when the cover has been removed and the cables are visible, American panelboards commonly have some live parts exposed. In Canadian service entrance panelboards the main switch or circuit breaker is located in a ''service box'', a section of the enclosure separated from the rest of the panelboard, so that when the main switch or breaker is switched off no live parts are exposed when servicing the branch circuits.<ref>{{cite book |date=2015 |title=C22.2 No. 29-15 — "Panelboards and enclosed panelboards" |publisher=Canadian Standards Association |isbn=978-1-77139-712-4 |page=40}}</ref>

===Breaker arrangement===
Breakers are usually arranged in two columns. In a U.S.-style board, breaker positions are numbered left-to-right, along each row from top to bottom. This numbering system is universal with numerous competitive manufacturers of breaker panels.

Each row is fed from a different line (''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 240&nbsp;V for [[split-phase electric power]], or 208&nbsp;V for [[Three-phase electric power|three-phase power]].

{| class="wikitable"
|+ North American breaker numbering
|-
! Split-phase
! 3-phase
! colspan="2" | Breakers
|-
| A
| A
| 1
| 2
|-
| B
| B
| 3
| 4
|-
| A
| C
| 5
| 6
|-
| B
| A
| 7
| 8
|-
| A
| B
| 9
| 10
|-
| B
| C
| 11
| 12
|-
| ⋮
| ⋮
| ⋮
| ⋮
|}{{cn|date=September 2023}}

====Interior====

The photograph to the right shows the interior of a residential service panelboard manufactured by [[General Electric]]. The three service conductors—two 'hot' lines and one neutral—can be seen coming in at the top. The neutral wire is connected to the neutral [[busbar]] to the left with all the white wires, and the two hot wires are attached to the main breaker. Below the main breaker are the two bus bars carrying the current between the main breaker and the two columns of branch circuit breakers, with each respective circuit's red and black hot wires leading off. Three wires (hot black, neutral white, and bare ground) can be seen exiting the left side of the enclosure running directly to a [[NEMA connector#NEMA 5|NEMA 5-15]] [[electrical receptacle]] with a [[power cord]] plugged into it. The incoming bare, stranded ground wire can be seen near the bottom of the neutral bus bar.

The photograph on the left shows a dual panel configuration: a main panel on the right (with front cover in place) and a subpanel on the left (with cover removed). The subpanel is fed by two large hot wires and a neutral wire running through the angled conduit near the top of the panels. This configuration appears to display two violations of the current U.S. National Electrical Code: the main panel does not have a grounding conductor (here it is fed through the subpanel instead) and the subpanel neutral bar is bonded to the ground bar (these should be separate bars after the first service disconnect, which in this case is the main panel).

<gallery caption="North American boxes" widths="100px" align="centre">
File:ElectricalPanel.jpg| An American circuit breaker panel featuring ''interchangeable'' circuit breakers

File:OpenClosedPanelboardEEUU(GE)CloseupTop.jpg | Illustration of breaker numbering in a North American type panelboard. Some labels are missing, and some are additional. The numbers on the [[toggle switch|toggles]] indicate the rated [[Ampere|amperage]] before tripping. The top right breaker (Rated at 100&nbsp;A) feeds a sub panel.

File:Electrical panel and subpanel with cover removed from subpanel.jpg| Electrical panel and subpanel with cover removed from subpanel.

File:EEUU(GE)BreakerpanelInnards.jpg| The internal wiring visible.

File:Murray-fuse-box.jpg| An older style fuse box of the variety used in the United States.
</gallery>

===Fuse boxes===


A common design of fuse box that was featured in homes built from 1940 through 1965 was the 60-amp fuse box that included four plug fuses (i.e. the Edison base) for branch circuits and one or more fuse blocks containing cartridge fuses for purposes such as major appliance circuits.<ref>{{cite book |url=https://books.google.com/books?id=QtVhK6z7mpQC&pg=PA75 |title=Black & Decker The Complete Guide to Wiring |edition=4th |year=2008 |author=((The editors of Creative Publishing )) |publisher=[[Cool Springs Press]] |page=75 |isbn=978-1589234130 |access-date=2014-06-15 |archive-date=2023-07-18 |archive-url=https://web.archive.org/web/20230718000620/https://books.google.com/books?id=QtVhK6z7mpQC&pg=PA75 |url-status=live }}</ref> After 1965, the more substantial 100 A panel with three-wire (230 V) service became common; a fuse box could have fuse blocks for the main shut-off and an electric range circuit plus a number of plug fuses (Edison base or Type S) for individual circuits.<ref>{{cite journal |journal=Popular Science |date=January 1966 |publisher=[[Bonnier Corporation]] |page=160 |title=Improving Your Home Wiring |first=Daniels |last=George |url=https://books.google.com/books?id=mikDAAAAMBAJ&pg=PA160 |access-date=2014-06-15 |archive-date=2023-07-18 |archive-url=https://web.archive.org/web/20230718000541/https://books.google.com/books?id=mikDAAAAMBAJ&pg=PA160 |url-status=live }}</ref>