Domestic Wiring and Illumination Questions and Answers

Answer: B

A quad is a group of four insulated conductors, usually twisted together in a cable, as in telephone and communication cables.

Two insulated conductors twisted together are a pair, and six or eight conductors would be a larger group with other names. In a 'star quad' cable the four conductors are twisted together to reduce the crosstalk between circuits. So the second option is the answer.

Answer: A

ICDP stands for Iron Clad Double Pole. An ICDP main switch is a double pole switch (one pole for the phase and one for the neutral) enclosed in an iron case for safety, and is fitted at the start of a domestic wiring installation to cut off the supply.

The other expansions, 'Insulated Core', 'Insulated Cable' and 'Instant Cutoff', are not the meaning of the letters. So the first option is correct.

Answer: D

The key gives 1.25 m as the length under which flexible conduit in a motor installation should be kept. Flexible conduit is used for the short connection between a rigid conduit run and a motor, which can move or vibrate, and it is kept short for mechanical protection and for earth continuity.

I could not check the figure in the wiring code, so the answer follows the key. The values of 10 m, 5 m and 2.5 m are longer than a flexible conduit should be. The fourth option is the one given.

Answer: C

The keyed maximum load on a power sub-circuit is 3000 Watt.

Indian wiring practice, following the Indian Electricity Rules and the code of practice for wiring, separates lighting and power circuits. A lighting sub-circuit is limited to about 800 W (or ten points), while a power sub-circuit, which feeds heavy appliances through 15 A outlets, is limited to 3000 W, with no more than two outlets on it.

800 W is the lighting sub-circuit limit, and 1000 W and 1500 W are not the figures the rules give for power circuits.

Answer: B

The cheap and temporary system is cleat wiring.

In cleat wiring, PVC or VIR insulated wires are held on the wall or ceiling by porcelain or plastic cleats screwed at intervals. It is quick to put up and take down and needs very little material, which makes it suitable for temporary installations such as at functions, construction sites and exhibitions. It is not protected from mechanical damage or weather and looks untidy, so it is not used for permanent work.

Conduit wiring is the most durable and expensive system, CTS (TRS) wiring is a cheap permanent system for houses, and casing-capping wiring encloses the wires in wooden or PVC channels for permanent use.

Answer: C

The total flux depends inversely on the utilization factor.

In the lumen method, the total lamp flux needed to give an illumination E over an area A is

\[ \Phi = \frac{E \times A}{UF \times MF} \]

where UF is the utilization factor (the fraction of lamp flux that reaches the working plane) and MF the maintenance factor. A higher utilization factor means fewer lumens are needed, so the flux is inversely proportional to it.

Illumination and surface area are in the numerator, so the flux is directly proportional to both. The space to height ratio affects the layout of the fittings and the uniformity of lighting, not the flux formula itself.

Answer: B

The pinch effect occurs in the core type induction furnace.

In a core type (low frequency) induction furnace the molten metal forms a ring that acts as a single-turn secondary carrying a very large current. The electromagnetic forces from that current squeeze the liquid metal inward, and at high current density they can pinch the metal column apart, breaking the secondary circuit and interrupting heating. That is the pinch effect, and it limits the power of these furnaces.

The coreless induction furnace heats the whole charge in a crucible and has no such narrow channel, and a resistance furnace heats by current through resistors, so neither suffers from it. The vertical core type furnace was designed to reduce the effect.

Answer: A

Magnetic materials are heated by hysteresis loss.

When a magnetic material is placed in an alternating magnetic field, its domains are magnetised back and forth every cycle, and the energy lost in each cycle (the area of the hysteresis loop) appears as heat inside the material. Together with the eddy currents induced in it, this is the basis of induction heating of magnetic metals, and the hysteresis heating stops once the material passes its Curie point.

An electric arc, conduction of current through the material and radiation are other heating methods, but they do not depend on the material being magnetic.

Answer: B

The wire with the highest current carrying capacity is 4 gauge.

In the standard wire gauges the number runs the opposite way to the size: the smaller the gauge number, the thicker the wire. A thicker wire has a larger cross-section and lower resistance per metre, so it heats less and can carry more current.

Of 4, 10, 12 and 18 gauge, 4 is the thickest and 18 the thinnest, so 18 gauge carries the least current and 10 and 12 gauge sit in between.

Answer: A

A mercury vapour lamp gives a greenish blue light.

The discharge in mercury vapour radiates mainly in a few spectral lines in the blue, green and yellow, with very little red. That makes the light look bluish green and distorts colours, which is why mercury lamps were used for street and factory lighting rather than where colour matters.

Yellow is the colour of the low-pressure sodium vapour lamp, and a neon discharge gives orange-red to pink light. White light needs a full spectrum, as from an incandescent or fluorescent lamp.