Switchboard (MDB,EMDB,DB,ATS,MTS) is one of the most important systems in the distribution system. It is responsible for preventing damage, controlling the power supply and receiving electricity from the electrical system, generators or transformer before distributing to organizations that need to use the electricity.


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Main Components of switchboard

It is made of metal sheet and is assembled as a cabinet. This may only be opened at front or opened at all sides depending on the design. Its main features are

1. Mechanical properties. Sufficiently support external mechanical strength for normal and non-normal use.

2. Thermal properties. Able to resist the heat from the environment, error in the system and arc from the short circuit.

3. Corrosion resistance properties. Resist to moisture and chemical corrosion. The cabinet also serves to prevent any possible harms which are

          a. Prevent the person near the switchboard from touching the exposed parts.
          b. Protect the equipment inside the cabinet from external things such as water, solid objects, reptiles, etc.
          c. Prevent severe damage from arc that the equipment may fall apart.


The conductor can be made of copper and aluminum. The most commonly used form of busbar is flat form with the rectangular cross-sectional area because it is easy to install and cooled down efficiently. It is divided into 2 types.

1. Naked busbar

2. Coated busbar

Tips for using the busbar

1. The busbar should be placed vertically so it will cool down well.

2. Flat busbar should be placed with no more than 4 bars in parallel. If exceeded, there is a problem with Skin Effect.

3. For coated busbar, coating colors should have a cooling coefficient of about 0.9.

4. Coated busbar has higher conductivity that naked busbar.

5. Red, Yellow, Blue for R, Y, B phase is specified, respectively.

6. The phase arrangement in the switchboard (R, Y, B) should be arranged from the front to the rear of the cabinet, from top to bottom or from left to right.

7. Another phase arrangement is allowed only when connecting to an existing system. However, sign must be marked clearly.


Circuit Breaker for switchboard

For low voltage switchboard, there are 2 types of commonly used breakers which are Air Circuit Breaker and Mold Case Circuit Breakers. Air CB is used as main breakers in high current circuits. Mold Case CB (MCCB) is used for branch circuit or used as a breaker in a small switchboard.

Selection of breakers should consider its width, length, height in order to fit in the board properly, IC currents including co-ordination.


Meter for switchboard

The basic measuring equipment used in the switchboard is voltmeter and ammeter which must be used with Selector Switch to measure the voltage or current in each phase. The voltage rating of the voltmeter ranges from 0-500V. Current rating of ammeter depends on the ratio of the current transformer, such as 100 / 5A.

For large switchboards, there may be P.F. Meter, Watt Meter or Var Meter depending on the board design. Some board may also be equipped with a P.F. Controller to control the power factor in the circuit.


Accessories for Switchboard

There are several components in the switchboard such as

1. Current Transformer (CT) for Switchboard. The device is used to measure current by connecting with the CT ammeter. CT meter used in the market is divided into 2 groups, the ratio of 1 and the ratio of 5. The ratio of 5 is commonly used in the switchboard such as 50/5, 100/5, 300/5, etc. Normally CT will be selected based on the size of the main circuit breaker but must be higher than breaker rating such as 100A main breaker must be used with CT of 100 / 5A. Use caution of CT is not to open the secondary circuit of the CT because it causes high voltage over the coil and cause the CT to burn. If there is no use of CT, the two terminals of the CT should be short circuited.

2. Selector Switch for Switchboard. The Ammeter Selector Switch is used with CT and Panel Ammeter to measure current in the switchboard. The Voltmeter Selector Switch is used with the Panel Voltmeter to measure the switchboard voltage. To connect the circuit, user should check the diagram that comes with the device. Because each brand has different circuit connection.

3. Plot Lamp for switchboard. It is a lamp that indicate the work status and to inform if there is power supplied to the switchboard or not. Pilot Lamp has two types which are.

          3.1 with potential transformer
          3.2 without potential transformer

The potential transformer will reduce the voltage to suit the voltage of the lamp, such as 220 / 6.3V.

4. Fuse for switchboard. Fuse is a glass tube that used to protect circuit of meter and Pilot Lamp.

5. Busbar insulator for switchboard. It is an insulator for busbar. One side is attached to switchboard while the other side will attach the busbar. There are many types of insulators to fit each types of busbar

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