Odisha CHSE +2 VOC-ITV Wireman Control Panel flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's law

For a resistive circuit, voltage equals current multiplied by resistance (V = I × R). Power can be found as P = V × I = I²R = V²/R.

Parallel resistance formula

The reciprocal of total resistance equals the sum of the reciprocals of individual resistances. For two resistors, RT = (R1 × R2)/(R1 + R2).

RMS value of sine

The root-mean-square value of a sinusoidal quantity equals the peak value divided by the square root of two, about 0.707 times the peak.

Power factor

The cosine of the phase angle between voltage and current, equal to real power divided by apparent power. It is 1.0 for pure resistance and zero for pure reactance.

Three-phase star relationship

In a star-connected system the line voltage is √3 times the phase voltage, while the line current equals the phase current. Total power is √3 × VL × IL × cos φ.

Conductor resistance formula

Resistance equals resistivity multiplied by length divided by cross-sectional area. Doubling the length doubles resistance; doubling the area halves it.

PVC versus XLPE insulation

PVC is thermoplastic with a 70 °C rating and softens on overload. XLPE is thermoset with a 90 °C rating and better short-circuit withstand, so it suits hot locations.

Conduit fill rule

The total cross-sectional area of cables in a conduit should not exceed 40 percent of the conduit internal area, allowing heat dissipation and easy drawing of conductors.

Standard Indian cable sizes

Common metric conductor sizes are 1.0, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70 and 95 square millimetres. Lighting uses 1.5 and sockets 2.5.

Crimping versus soldering

Crimping with a matched lug and tool gives a mechanically and electrically sound joint without heat damage and is preferred in control panels over soldered terminations.

Bimetallic lug

A lug made for joining aluminium conductors to copper busbars, preventing galvanic corrosion at the joint. Anti-oxidant compound is applied to aluminium strands before crimping.

Two-way switch control

Two two-way switches connected by two strapper wires allow a lamp to be controlled from either of two positions. An intermediate switch extends control to three or more points.

Indian phase colour code

Three-phase conductors are red, yellow and blue; neutral is black or blue; earth is green or green-yellow. Single-phase live is red or brown.

Loop-in lighting wiring

Live, neutral and earth are looped from ceiling rose to ceiling rose, with the switch drop taken from each rose. Fewer concealed joints make it preferred over joint-box wiring.

Cable derating factors

The tabulated current rating is multiplied by correction factors for ambient temperature, grouping of circuits, and installation method to obtain the actual permissible current.

Voltage drop limit

Installation design keeps voltage drop within 3 percent on a final sub-circuit and 5 percent from the supply origin to the load, ensuring equipment receives adequate voltage.

Contactor auxiliary contacts

Small normally-open and normally-closed contacts mechanically linked to the main contactor, used in control circuits for holding, interlocking and indication at low current.

MCB trip curves

B curve trips at 3 to 5 times rated current for resistive loads, C curve at 5 to 10 times for general use, and D curve at 10 to 20 times for motors.

Thermal overload relay setting

The relay is set to the motor full-load current. Class 10 suits normal starting, while class 20 or 30 allows the longer starting times of high-inertia loads.

Emergency stop push button

A red mushroom-head latching button with normally-closed contacts that removes control power and stays latched until deliberately reset, preventing unexpected restart.

DOL starter

Direct-on-line starting applies full line voltage to the motor through a contactor and overload relay. It is simple and cheap but draws six to eight times full-load current.

Star-delta starting principle

The motor starts in star, reducing phase voltage to line voltage divided by √3, so starting current and torque fall to one third. It then changes to delta for run.

No-volt protection

A contactor drops out when supply fails and does not re-energise on restoration until the start button is pressed again, protecting people from unexpected machine restart.

Forward-reverse interlocking

Two contactors controlling opposite rotation are fitted with normally-closed auxiliary contacts in each other's coil circuit, so both can never energise at the same time.

Variable frequency drive

A drive varies both frequency and voltage applied to a motor, giving controlled acceleration, speed control and energy saving on variable-torque loads such as fans and pumps.

Earth pit resistance

Earthing resistance should not exceed 1 ohm for a substation and is generally kept within 5 ohms for domestic installations. It is measured with an earth tester.

30 mA RCD

A residual current device that trips when earth leakage exceeds 30 milliamperes, protecting people from electric shock. It does not protect against overload or short circuit.

Safe isolation procedure

Identify the circuit, isolate and lock off, prove the tester on a live source, test the conductors dead, then re-prove the tester before touching anything.

Megger insulation test voltage

Use 500 volts DC for low-voltage circuits and 1000 volts for low-voltage cables and motors. A reading of at least 1 megohm is normally acceptable.

Clamp meter principle

The instrument measures current from the magnetic field around a single conductor without breaking the circuit. Clamping two conductors together cancels the reading.

IS 732 and IS 3043

IS 732 is the code of practice for electrical wiring installations covering design, protection and testing. IS 3043 is the code of practice for earthing.

Permissible supply voltage variation

Indian regulations permit low-voltage supply variation of plus or minus 6 percent, with frequency held at 50 hertz within plus or minus 3 percent.

Panel estimation line items

A panel estimate lists enclosure, busbars, switchgear, contactors, relays, wiring, ferrules, terminal blocks, labels, painting and testing, then adds labour, overheads, profit and GST.