SSC JE 2014 Electrical question paper with solution(Evening-shift)

If the conduit wiring, steel tubes  are installed on the surface of walls by means of pipe hooks (surface conduit wiring)

Surface conduit wiring is best suitable for workshops, Industries, and laboratories. because in concealed wiring system alternation of light position after full setup is virtually impossible.

Various specifications in respect to earthing as recommended by Indian Standards are given below.

An earthing electrode should not be installed close to the building whose installation system is being earthed at least more than 1.5m away.

The earthing electrode should always be placed in a vertical position inside the earth or pit so that it may be in contact with all the different earth layers.

Just after the supply, the consumer must provide the main switch which would control the complete lighting and power circuit of the house. This switch operates simultaneously on the live phase and neutral.

The fuse unit box is generally sealed by the supplier and the consumer does not have the authority to replace or repair the fuse. In case of blowing out, the authorized person appointed by the electric supply company is only permitted to replace the blown-out fuse.

Indian Electricity Rules specify that the maximum load on a light/fan sub-circuit should not exceed 800 watts and the number of points should be limited to 10.

The earth pin on a plug is longer than the live and neutral pins. This means the earth pin is the first to connect and the last to disconnect.

• When inserting the plug, the earth connection is made before the current-carrying contacts of the plug become live.
• When withdrawing the plug, the current-carrying contacts shall separate before the earth connection is broken.

Earth resistance should be as small as possible. It depends on the voltage level of the system to be grounded. As the voltage level increases the earth’s resistance is required to be nearer to zero as far as possible. The NFPA and IEEE recommend a ground resistance value of 5 ohms or less.

For domestic application, the earth resistance should be between 0.2 – 0.5 ohms

The earthing electrode should always be placed in a vertical position inside the earth or pit so that it may be in contact with all the different earth layers.

The load factor is defined as the average load divided by the peak load in a specified time period.

Load factor = Average load/ Maximum Demand

Diversity factor = Sum of individual maximum demand/ Station maximum demand.

Both load factor and diversity factors are inversely proportional to maximum demand. A higher load factor and diversity factor mean steady consumption or supply which means less maximum demand thus the initial and running cost will be low. Therefore the cost per unit of power generation will be less.

A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 589 nm.

There are two varieties of such lamps: low pressure and high pressure. Low-pressure sodium lamps are highly efficient electrical light sources, but their yellow light restricts applications to outdoor lighting such as street lamps.

High-pressure sodium lamps produce a broader spectrum of light than low-pressure lamps, but they still have poorer color rendering than other types of lamps. Low-pressure sodium lamps only give monochromatic yellow light and so inhibit color vision at night.

A welding power supply is a device that provides an electric current to perform welding. Welding usually requires high current (over 80 amperes) and it can need above 12,000 amperes in spot welding.

A welding transformer is a step-down electrical transformer that converts the moderate voltage and moderate current electricity from the utility mains (typically 230 or 115 VAC) into a high current and low voltage supply, typically between 17 and 45 (open-circuit) volts and 55 to 590 amperes.