A distribution board (DB) is where the electrical supply is distributed from within the building. The main supply cable comes into the board and is then distributed to the breakers and from there to all the circuits, e.g. lights, plugs. It usually houses all the contact breakers, earth leakage unit and may house items such as a door bell transformer and timers. Various sizes of distribution boards are available.
The main distribution board is usually in the house where the main electrical cable enters and smaller boards, together with contact breakers and possibly earth leakage units are at other points, such as swimming pool pumps, gate motors and outbuildings. Various types of distribution boards are available; as surface mounted, flush mounted or floor standing; with closing doors or see through plastic covers or doors and in diﬀerent sizes which are determined by the number of circuits rewired within the board to which some manufacturers refer to as modules and others as “way” e.g. 8, 12, 18, 24, 36, etc. way or module.
The interior of the distribution board is pre-fitted with a clip tray or DIN rail for mounting the miniature circuit breakers (MCB) and other devices. These two diﬀerent types of MCB’s referred to as “mini rail” or “DIN” which are only interchangeable if special adaptor brackets are used. While mini rail MCB’s can be slightly narrower than DIN MCB’s thus giving an advantage of fitting more into the same space available the number of accessories on the market for this type of distribution board is limited as many manufacturers are now using the DIN format for their equipment. With the DIN format, the normal range of earth leakage units, disconnecting switches as well as MCB’s are available.
In addition to this, various types of meters, time switches, pilot lights, surge arresters, etc. are manufactured as well as GSM (Global System for Mobile Communications) units to facilitate remote monitoring and control of events via a cell phone. This now makes the DIN type of distribution board very versatile. Distribution boards can be purchased either as an empty enclosure to enable the contractor to equip it, or as a ready wired standard unit, or as a specially manufactured item to the client’s requirements. Also available are distribution boards for specific applications such as swimming pools, ready boards for low-cost housing, irrigation systems, etc. Each distribution board must be controlled by a switch disconnector (mains or main switch).
Each distribution board must be controlled by a switch disconnector (mains or main switch) The switch disconnector should:
- Be mounted in or next to the distribution board.
- In the case of the main or first distribution board of an installation, be labeled as “main switch”.
- In the case of a sub-distribution board, be labeled as “sub-main switch” or “main switch” if the board is labeled “sub-board”.
- In the case where an alternative supply is installed (emergency supply, uninterruptible power systems (UPS), etc.), be labeled as required.
- Have a danger notice on or near it. The danger notice should give instructions that the switch disconnector be switched oﬀ in the event of inadvertent contact or leakage.
A distribution board must comply with the requirements of SANS 10142, and each item of electrical equipment used in a distribution board should comply with the requirements of this standard:
- The distribution board must be suitable for the environmental conditions in which it operates.
- Distribution boards shall be protected against corrosion.
- Any point of a distribution board that has to be reached during normal operation, must not exceed a height of 2200 mm above floor (or walking) level. However, the board may be mounted higher if it can be disconnected from the supply by a switch disconnector that is less than 2.200 mm above floor level. Unless a residential distribution board is housed in an enclosure and direct access cannot be obtained by an infant, no part of an indoor distribution board can be less than 1.200 mm above the floor level, and no part of an outdoor distribution board can be less than 0.200 mm above the ground level.
- A distribution board must not be mounted in a bathroom, or above a fixed cooking appliance, or in a position where a stationary cooking appliance could be put below it, unless the enclosure provides a degree of protection, or within a radius of 1 m from a water tap or valve (in the same room), unless the enclosure provides a degree of protection.
- If an installation is likely to be extended, a distribution board with spare capacity should be fitted.
- Each unoccupied opening of a distribution board must be fitted with a blanking plate.
- Unless obvious, permanent labeling must identify all incoming and outgoing circuits of the distribution board.
Information supplied by Buildaid Publishing.