GUIDED BY- Mr. Bipin saxena PRESENTED BY – Giri Pankajkumar Shyamkant ENROLLMENT NO Patel Harsh Mukesh bhai ENROLLMENT NO Sevak jigar Ketanbhai ENROLLMENT NO Elements of Electrical Engineering

Earthing AND ELECTRICAL SAFETY

Earthing The process of connecting metallic bodies of all the electrical apparatus and equipment to huge mass of earth by a wire having negligible resistance is called Earthing.

Qualities Of Good Earthing Must be of low electrical resistance Must be of good corrosion resistance Must be able to dissipate high fault current repeatedly

ELECTRICAL SAFETY ELECTRICAL SAFETY Effects of Amount of AC Current 3 ma- painful shock which cause indirect accidents 10ma- muscle contraction...”no let go” danger 30ma- lung paralysis- usually temporary 50ma- possible ventricular fibrillation (heart dysfunction, usually fatal) 100 ma- certain ventricular fibrillation, fatal 4 amps- heart paralysis, severe burns

Electrical Shock Received when current passes through the body. Severity of the shock depends on: Path of current through the body Amount of current flowing through the body Length of time the body is in the circuit LOW VOLTAGE DOES NOT MEAN LOW HAZARD!

Protective devices

TYPES OF ELECTRICAL PROTECTIVE DEVICES

TYPES OF FUSE

DIFFERENT TYPES OF MCB(MINIATURE CIRCUIT BREAKER) MCCB (MOLDED CASE CIRCUIT BREAKER)

Characteristics of MCB Rated current up to 1000 A. Trip current may be adjustable. Thermal or thermal-magnetic operation. Characteristics of MCB Rated current not more than 100 A. Trip Characteristics normally not adjustable. Thermal or thermal-magnetic operation.

 The first characteristic is the overload which is intended to prevent the accidental overloading of the cable in a no fault situation. The speed of the MCB tripping will vary with the degree of the overload. This is usually achieved by the use of a thermal device in the MCB.  The second characteristic is the magnetic fault protection, which is intended to operate when the fault reaches a predetermined level and to trip the MCB within one tenth of a second. The level of this magnetic trip gives the MCB its type characteristic as follows: TYPETRIPING CURRENTTRIPPING TIME Type B 3 To 5 time full load current 0.04 To 13 Sec Type C 5 To 10 times full load current0.04 To 5 Sec Type D 10 To 20 times full load current0.04 To 3 Sec

The third characteristic is the short circuit protection, which is intended to protect against heavy faults maybe in thousands of amps caused by short circuit faults. The capability of the MCB to operate under these conditions gives its short circuit rating in Kilo amps (KA). In general for consumer units a 6KA fault level is adequate whereas for industrial boards 10KA fault capabilities or above may be required. The third characteristic is the short circuit protection, which is intended to protect against heavy faults maybe in thousands of amps caused by short circuit faults. The capability of the MCB to operate under these conditions gives its short circuit rating in Kilo amps (KA). In general for consumer units a 6KA fault level is adequate whereas for industrial boards 10KA fault capabilities or above may be required.

 Fuses and MCBs are rated in amps. The amp rating given on the fuse or MCB body is the amount of current it will pass continuously. This is normally called the rated current or nominal current.  Many people think that if the current exceeds the nominal current, the device will trip, instantly. So if the rating is 30 amps, a current of amps will trip it, right? This is not true.  The fuse and the MCB, even though their nominal currents are similar, have very different properties.  For example, For 32Amp MCB and 30 Amp Fuse, to be sure of tripping in 0.1 seconds, the MCB requires a current of 128 amps, while the fuse requires 300 amps.  The fuse clearly requires more current to blow it in that time, but notice how much bigger both these currents are than the ’30 amps’ marked current rating.  There is a small likelihood that in the course of, say, a month, a 30-amp fuse will trip when carrying 30 amps. If the fuse has had a couple of overloads before (which may not even have been noticed) this is much more likely. This explains why fuses can sometimes ‘blow’ for no obvious reason  If the fuse is marked ’30 amps’, but it will actually stand 40 amps for over an hour, how can we justify calling it a ’30 amp’ fuse? The answer is that the overload characteristics of fuses are designed to match the properties of modern cables. For example, a modern PVC- insulated cable will stand a 50% overload for an hour, so it seems reasonable that the fuse should as well.

ELCB (Earth Leakage Circuit Breaker) Characteristics Phase (line), Neutral and Earth wire connected through ELCB. ELCB is working based on Earth leakage current. Operating Time of ELCB: The safest limit of Current which Human Body can withstand is 30ma sec. Suppose Human Body Resistance is 500Ω and Voltage to ground is 230 Volt. The Body current will be 500/230=460mA. Hence ELCB must be operated in 30maSec/460mA = 0.65msec