PROTECTION OF THE BRANCH CIRCUIT

Transcription

1 PROTECTION OF THE BRANCH CIRCUIT

2 Branch circuit should always be protected from over current. Hence, an overall current devices shall be installed in all branch circuitries.

3 Function of the over-current protective devices. Open the circuit (disconnect the line) when the current rating capacity of the equipment being protected is exceeded. The circuit protective device represents the source of voltage due to it being the medium between the hot end of the voltage source and the load end of the circuit wiring.

4 Causes of overcurrent 1. Overload in the equipment conductors. 2. Short circuit or ground fault. Regardless whether the excess current is caused by equipment overloading or un-intentional ground fault --- protective devices must interrupt the line; called clearing

5 Over-current protective devices are installed to protect the following: 1) The wiring 2) The transformer 3) The lights 4) Appliances and other equipment

6 Overcurrent Definition: any current in excess of the rated capacity of the equipment or the rated ampacity of the conductor.

7 Application of the Over-current Protection is also Governed by ff: 1. Overcurrent devices should be installed on the line or supply side of the equipment being protected. 2. Overcurrent devices shall be placed in all underground conductors of the protected circuits. 3. All equipment should be protected in accordance with its current carrying capacity

8 Application of the Over-current Protection is also Governed by ff: 4. Overcurrent protective devices should be readily assembled and protected from physical damages and away from easily ignited materials. 5. Conductor size should not be reduced in a circuit or tap unless the smallest wire is protected by the circuit overcurrent devices.

9 Fuse, Breaker and Panel Board

10 Fuse Definition: an overcurrent protective device with a circuit opening fusible element which opens (breaks) when there is an overcurrent in the circuit *One time protective device to be replaced after the fault is cleared *Simplest and common type

11 Types of Fuse Generally, fuse consists of fusible link or wire that easily melt at low temperature classified into two types: 1. Cartridge Type enclosed in insulating fiber tube 2. Plug Fuse Type enclosed in a porcelain cap

12 Circuit Breaker Overcurrent protective device designed to function as a switch. Equipped with an automatic tripping device to protect the branch circuit from overload and ground fault. Can be manually tripped Tripping cutting-off or disconnection of current supply

13 Advantages of Circuit Breaker over Fuse 1. The circuit breaker act as switch aside from its being an overcurrent protective device. 2. The Fuse,once busted due to overcurrent flow, has to be discarded while circuit breaker trips off automatically and after correcting the fault, it is again readily available for switching on.

14 Advantages of Circuit Breaker over Fuse 3. Circuit breaker can be multiple pole installed with 1,2 or 3 poles which will simultaneously protect and switch one to 3 lines. The fuse on the other hand, is a single pole, installed on a single wire that could only protect a single electric line. 4. The circuit breaker position is easier to detect. It could be closed, tripped, or open right at the handle. On the contrary, the busted fuse could not be detected easily because the melted fusible element is inside the casing.

15 Advantages of Circuit Breaker over Fuse 5. The circuit breaker can be manually tripped so that in many cases, it also acts as the circuit switch.

16 Advantages of Fuse over Circuit Breaker 1. Reliability and stability. The fuse can stay on its position for years and act when called to act as designed. 2. The cost of the fuse is very much lower compared to that of circuit breaker. 3. Circuit breakers has several moving parts which requires maintenance and periodic testing to be in good condition at all time.

17 Panel Board A single panel or group of panel units designed for assembly in the form of a single panel. including buses and automatic overcurrent devices, designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support accessible only from the front.

18 Principles Applied in Installing Panel Board 1. The approach shall be accessible and more convenient. 2. Centrally located to shorten the home wiring runs. 3. Must be installed near the load center, as in most cases panel boards are mounted near the kitchen and laundry where heavy loads are expected.

19 Principles Applied in Installing Panel Board 4. To limit voltage drop on the branch circuit, the panel board shall be located in such a manner that no circuit exceed 35 meters long. 5. In the event that a circuit more than 35 meters long cannot be avoided, No. 10 AWG wire shall be used for runs up to 50 meters long and No. 8 AWG for longer wiring connections.

20 Installation of Panel Board a. Panel board with 100 cm high or less should be located 135 cm from the floor to the center line of the box. b. Panel boxes over 100 cm high should be located 75 cm from the floor to the bottom of the box, except the highest branch unit should not be more than 195 cm from the floor.

21 Installation of Panel Board c. If necessary, the box maybe lowered to a distance not less than 45 cm from the floor to the bottom of the box. However, where a maximum height of 195 cm above the floor to the upper circuit or minimum distance of 45 cm above the floor cannot be done, the panel should be divided into two sections. d. If two or more boxes are adjacent on the same wall, they should be installed with the horizontal center line of each box equidistant from the floor. The center line distance of the higher box should be installed with a minimum spacing of 10 cm apart.

22 Other features of the Overcurrent Protective Device 1. The overcurrent device is always upstream of the equipment being protected. Meaning, electricity is ahead of the load. 2. Electric current flows downstream, and to cut off excess current, the protective device should be placed ahead of the protective items.

23 Other features of the Overcurrent Protective Device 3. The panel is the source of current, the overcurrent protective device is inside the electrical panel that supplies electric current. 4. The upstream side of the device is called Line Side. The downstream side is called the Load Side.

24 Switchboard and Switchgear Free standing assemblies of switches, fuses and circuit breakers that proving switching and feeding protection to a number of circuits connected to the main source.