BTEB Electrician (EIM) Exam flashcards

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

Ohm's law

For a conductor at constant temperature, the current is directly proportional to the applied voltage and inversely proportional to resistance: I = V/R, V = I × R, R = V/I.

Three-phase power formula

For a balanced three-phase load, total power P = √3 × line voltage × line current × power factor. For unity power factor the √3 factor still applies.

Star-delta voltage relation

In a balanced star connection, line voltage equals √3 times phase voltage and line current equals phase current. In delta, line voltage equals phase voltage and line current is √3 times phase current.

Resistors in parallel

The reciprocal of the total resistance equals the sum of the reciprocals of the individual resistances. For two resistors, total resistance is their product divided by their sum.

Insulation class F

An insulation class rated for a maximum winding temperature of 155 degrees Celsius. Class B is 130, class H is 180, and class C is above 180 degrees Celsius.

XLPE insulation

Cross-linked polyethylene insulation, rated for a continuous conductor temperature of 90 degrees Celsius. It carries more current and withstands higher overload than PVC, rated at 70 degrees Celsius.

Aluminium conductor drawback

Aluminium has higher resistivity than copper and forms an oxide film, so joints need antioxidant paste and bimetallic connectors to avoid electrolytic corrosion when joined to copper.

Crimping rule

A correct crimp uses the lug and die matched to the conductor size. It leaves no loose strands, passes a pull test, and is then insulated or covered with heat-shrink.

Wire stripping precaution

Set the stripper to the conductor gauge so strands are not nicked. A nicked strand reduces current capacity and can create a hot spot under load.

Ring circuit test

A ring final circuit returns to the board. Continuity of line, neutral and protective conductors must each be verified end to end to prove the ring is unbroken.

Two-way switching

Two switches control one lamp using two strapper wires between them plus a common and a switched live. Intermediate switches are inserted in the strappers for three or more control points.

IEC cable colours

Modern IEC colour code: brown for line, blue for neutral, and green-yellow for the protective earth conductor. Older UK wiring used red, black and green.

MCB type C

A miniature circuit breaker that trips magnetically at 5 to 10 times its rated current. It suits inductive loads with moderate inrush, such as small motors and transformers.

RCD purpose

A residual current device compares line and neutral current. If the difference exceeds its rating, typically 30 mA, it trips within 300 ms, protecting people from earth leakage.

Earth fault loop impedance

The total impedance of the fault path from the source through the live conductor and back via the protective conductor. It must be low enough for the device to trip within the required time.

IP rating digits

The first digit shows protection against solids on a scale of 0 to 6, and the second shows protection against water on a scale of 0 to 8. Higher numbers mean greater protection.

Transformer EMF equation

The induced EMF in a winding equals 4.44 times frequency times turns times maximum flux. The constant 4.44 comes from the sinusoidal waveform form factor of 1.11.

Induction motor slip

Slip equals synchronous speed minus actual rotor speed, divided by synchronous speed. Rotor frequency equals slip times supply frequency, and slip rises with load.

Synchronous speed

The speed of the rotating magnetic field, calculated as 120 times frequency divided by the number of poles. A four-pole motor on 50 Hz runs at 1500 rpm.

Transformer maximum efficiency

A transformer reaches maximum efficiency when its variable copper loss equals its constant core loss. Core loss stays nearly fixed, while copper loss rises with the square of load current.

DOL starter holding contact

A normally open auxiliary contact on the contactor, wired in parallel with the start button, keeps the coil energised after the button is released. The stop button opens the coil circuit.

Star-delta interlock

Star and delta contactors must never close together, because that short-circuits the supply. Electrical interlock through normally closed auxiliary contacts plus a timer prevents this.

Thermal overload relay

A bimetal device set to the motor full-load current. It protects the motor winding from sustained overcurrent but does not protect people from electric shock.

Insulation resistance test

Apply 500 volts DC to a 230/400 volt circuit with electronics disconnected. A healthy reading is at least 1 megohm, measured between line, neutral and earth in turn.

Polarity check

Confirms the line conductor reaches the centre contact of the lamp holder and the switch is fitted in the line conductor, not the neutral, so the lamp is dead when switched off.

Fault finding order

Work logically from supply to control to load. Confirm the symptom, test each stage, identify the fault, repair it, then retest and record the result.

Estimation wastage allowance

When taking off quantities, add about 5 to 10 percent for cable and 3 to 5 percent for accessories to cover offcuts, damage and future alterations.

As-built drawing

A drawing updated to show the installation as actually built, including any changes made during construction. It is essential for future maintenance and modification.

LED series resistor

The resistor value equals supply voltage minus LED forward voltage, divided by the desired current. A typical LED drops about 2 volts and needs 10 to 20 milliamps.

Thyristor turn-off

A thyristor latches on when gated with the anode positive. It stops conducting only when the anode current falls below the holding current, so it cannot be turned off by the gate.

Prove dead procedure

After isolation and locking off, test the voltage indicator on a known live source, test the circuit at all conductors, then re-test the indicator to confirm it still works.

Earth conductor rule

The protective earth conductor must be the last to be disconnected and the first to be reconnected when working on a circuit, so the earth path is never left open.