Earth Leakage Circuit Breaker

Earth Leakage Circuit Breaker Points :Earth Leakage Circuit Breaker, Earth Leakage Trip or Circuit Breaker, Use of Earth Leakage Circuit Breaker, Use of Earth leakage Trip with Electric Cooker, Plate Earthing, cross-sectional of the earthing lead, Cross-section of the earth continuity conductor Use of Earth Leakage Circuit Breaker According to Indian Standard ft is not necessary to use an earth leakage circuit breaker at a place where the earth impedance does not exceed 5 ohms with normal soil and 8 ohms with dry and rocky soil. But where the condition of earth is such that this low value of earth impedance is not available and the fuse wire does not melt or the circuit breaker does not fall open before the leakage current rises to a dangerously high value, an earth leakage circuit breaker is to be installed with each earth electrode in a wiring, system in order to have effective earthing.

An earth leakage circuit breaker is to be installed keeping in mind the following arrangement for this purpose. Earth leakage circuit breaker (full name is V voltage operated earth leakage circuit breaker’) should remain connected between consumer’s earth terminal and a suitable earth electrode. Insulated wires must be used for its connection. The electrode with which it is connected must remain outside the resistance area of any other earth electrode, especially where an extra electrode is used for a wiring system. Earth Leakage Trip or Circuit Breaker The purpose of installing such device (earth leakage trip) in an earthing circuit is that, when leakage current is high, this current flows through the relay of this device and attracts its armature. As a result the metal lever or switch blade falls open and completes the connection of another circuit through which the current starts flowing. The current opens the current breaker of that circuit in which the current is leaking. Hence, the leakage of current is stopped and the possibility of any accident is removed. Types of Earth Leakage Circuit Breaker or Earth Leakage Trip Earth leakage circuit breaker is available in three different types — single-pole, double pole ale and four-pole. Where supply is given by 3-phasc, 3-wire or 4-wire, a four-pole trip is used. For an ordinary house connected to low voltage supply line, a single-pole trip is sufficient.

Earth leakage circuit breaker has a relay coil. This coil is connected in series with the earthing wire of heater, cooker etc. and is separately earthed. Whenever there is any leakage of current in any appliance, the leakage current flows into the earth through the relay coil. As a result the coil is excited and acts as an electro-magnet which opens a contact inside. The main current of the circuit then flows through this contact.

Therefore if the earth wire of a house is connected with this trip coil which is separately earthed, as soon as the leakage current rises to 30 mA at any part of the circuit, at once the flow of current through the circuit is stopped. For a house this type of device is made in such a way that a current of 15 to 30 amperes can flow continuously through it. The device works effectively for both a.c. as well as d.c. supply. When the potential difference across the relay coil rises up to 20 to 30 volts, at once it starts working. Relay coil should be connected to its separate earth electrode by means of insulated wires. This separate earth electrode must be at least 1.83 metres (6 ft) away from the main earth electrode of the house. The device has insulated cover over which a push switch is provided. The working of the relay can be tested by operating this switch. When the knob of the switch is pressed, the current flows from the line into the relay coil and the circuit opens. The connection of the push switch with relay coil has been shown in figure.

Use of Earth leakage Trip with Electric Cooker In a house where electric cooker is used, an earth leakage trip is essential for the sake of safety. If there is V.I.R. or P.V.C. or C.T.S. with in the house, the relay coil of the earth leakage trip should be connected to from frame of the cooker by means of insulated wire and separately earthed. When there is lead covered wiring or conduit wiring, the connecting wire for the relay coil is tapped from a suitable bonding point of the earthing circuit. For the protection of a cooker or any other fitting, its metal frame is connected to relay coil of the trip. However, for the protection of the house as a whole, the earth leakage trip is installed near the main distribution board, and the connecting wire for the relay coils tapped from main earthing lead of the house at a suitable point and drawn up to a separate earth electrode by means of insulated wires. If one desires, an earth leakage circuit breaker may be used with an appliance operated through a 3-pin plug. In this case 3-pin plug and the leakage trip should be mounted on the same block. This is shown in figure.

The connection of a push switch is shown in figure below. When the knob of the push switch is pressed, its contact touches the terminal of a resistance. This causes the current drawn by the apparatus to flow directly into the test resistance from the upper terminal on the right-hand side and then trough the relay coil. As a result the relay becomes a strong electro-magnet which opens the circuit. The earth lead used must be G.I. wire or G.I. strip (not of copper) of water should be put upto the funnel connected to the main GJ. pipe through 19mm. Dia. Pipe.

The earth lead used must be G.I. wire or G.I. strip (not of copper) of sufficient cross-sectional area to carry fault current safely. (It - should not be less than electrical equivalent of copper conductor of 12.97 sq. mm (8 SWG) cross-sectional area. The earth wire from the Gi pipe of 19mm dia. Should be carried in a G.I. pipe of dia. 12.7 mm.

At a depth of about 60 cm. Below the ground Further when the earth wire is carried over from one machine to the other, it should be well protected from mechanical injury; be carrying the earth wire in a recessed portion.

Plate Earthing The earth connection can again be provided with the help of a copper plate or GE pipe. When G.I. plate is used it should not be of less than 60cm x 60cm. ) 6.35mm while for copper plate these dimensions may be 60cm. X 60cm. X 3.18 mm. However, the use of the copper plate in these days, is limited. Points to remember while providing Earthing Following point should be remembered while providing earthing to an installation and premises. Various details given as per 1.S. specification are: (i) Distance The distance of the electrode from the installation at the premises should be more than 1 .5 meter. (ii) cross-sectional of the earthing lead It should never be less than half the cross-section of the mains wire or. conductor. The selection should be made in such a way that even in worst condition it shall not fuse out. The minimum size of the earthing lead should not be less than electrical equivalent of copper conductor of 8 SWG (12.97 sq. mm cross-section). The sizes of earthing lead for various loads and installations are given in Table 10.1 (iii) Cross-section of the earth continuity conductor The size of the earth continuity conductor should not be less than 14 SWG (2.894 sq. mm) (iv) Electrode As already discussed, the earthing can be done either with plate or pipe electrode. It should be remembered that the material for earth electrode and earth lead should be same material for earth electrode and earth lead should be same and the electrode should always be placed in vertical position. The size of the plate earth electrode for various loads and insulation should be in accordance with the details given in Table. (v) Earth resistance The earth resistance of any earthing should not be more than 5 ohms. As already said that for better performance at power house and sub-stations or for high horse power motor beyond 100 H.P. the earth resistance should be upto 0.5 ohm and 1 ohm respectively.