How do you decide what size of electrical wire do you need?

The proper size of wires mainly depends on the amount of load current & voltage supplied as well as the length of the cable. Usually, the voltage drop in cables should not be greater then 2.5% of the supply.

• Measure the supply voltage.
• Calculate its 2.5% allowable voltage drop.
• Measure the required length of the cable in meters.
• Divide the allowable voltage drop with the length.
• The resultant is the max allowable voltage-drop per meter & your required cable size should have a lower voltage drop than this.
• Calculate your load current.

The cable charts provide this info such as voltage-drop per meter, current capacity, cable size, etc. match your calculation with the chart & find you required cable size. 

Define the term Capacitance and Inductance

Capacitance: capacitance is the ability of a component to store charge between two plates when there is a potential difference applied. It is denoted by C & it is measured in Farads F.

Inductance: inductance is the ability of a conductor to resist or oppose any change in the current. The current generates a magnetic field whose strength varies with the current. It is denoted by L & is measured in Henry H.

Why Motor rated in kW instead of kVA?

As we know the transformer is rated in KVA because its PF (Power Factor) depends on the nature of the loads. However, Motor has a fixed power factor, i.e. motor has defined power factor (P.F) and the rating has been mentioned in kW or HP on Motor. In more clear words, Motor only consumes active power and provides mechanical power in HP or kW at the motor shaft and that is the reason for motor ratting in watts.

Why do we improve the power factor?

The reason for improving power factors are stated below;

• Large Line Losses (Copper Losses): Line losses (I²R) depend on current. The low power factor draws a large amount of current as compared to the high power factor.
• Large kVA rating and Size of Electrical Equipment; PF is inversely proportional to KVA. Low PF equipment with a high KVA rating is larger in size.
• Large Conductor Size and Cost; we need large conductors to transmit the heavy current required due to low power factor.
• Poor Voltage Regulation and Large Voltage Drop; The large current due to low PF causes a high voltage drop that needs to be regulated more often than usual.
• Low Efficiency; The losses due to the high current flow & voltage drop deteriorate the efficiency of the system. The efficiency is maximum at PF=1.

Why the current transformer’s secondary should not be open when there is current flow in its primary?

The current transformer is essentially a step-up transformer that increases the voltage & decreases the current on the secondary side. Under the open secondary condition, the primary current becomes the magnetizing current that generates a very high secondary voltage that can damage the insulation as well as can pose danger to personnel.

Why Human body feel Electric shock ?? n in an Electric train during running , We did nt feel any Shock ? why?

Unfortunately our body is a pretty good conductor of electricity, The golden rule is Current takes the lowest resistant path if you have insulation to our feet as the circuit is not complete (wearing rubber footwear which doing some repairs is advisable as our footwear is a high resistance path not much current flows through our body).The electric train is well insulated from its electrical system.

How tube light circuit is connected and how it works?

A choke is connected in one end of the tube light and a starter is in series with the circuit. When supply is provided ,the starter will interrupt the supply cycle of AC. Due to the sudden change of supply the chock will generate around 1000 volts . This volt will capable of to break the electrons inside the tube to make electron flow. once the current passes through the tube the starter circuit will be out of part. now there is no change of supply causes choke voltage normalized and act as minimize the current.