TP EIMSA flashcards

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

Touch voltage limit

Maximum permissible touch voltage under IEC 60364-4-41 is 50 V AC or 120 V DC in ordinary locations, reduced to 25 V AC or 60 V DC in wet or confined conductive locations.

Earth-fault loop impedance

Zs must not exceed U0 divided by Ia, where Ia is the current causing the protective device to operate within the required disconnection time for that circuit.

RCD 30 mA purpose

A 30 mA residual current device provides additional protection against electric shock for socket-outlets up to 32 A and for circuits in locations with increased shock risk.

IP code meaning

The IP rating states ingress protection: first digit for solids from 0 to 6, second digit for water from 0 to 9K, for example IP65 is dust-tight and jet-proof.

Arc flash incident energy

Incident energy at a working distance depends on bolted fault current, protective device clearing time, electrode gap and working distance, and determines the required PPE category.

Three-phase power formula

For a balanced three-phase load, active power P equals root three times line voltage times line current times power factor; reactive power uses sine of the angle.

Star-delta relationships

In a star connection line voltage is root three times phase voltage and line current equals phase current; in delta the reverse applies to current and voltage.

Per-unit impedance

Per-unit impedance equals actual impedance divided by base impedance, where base impedance is base voltage squared divided by base apparent power.

Synchronous speed

Synchronous speed of an induction motor equals 120 times supply frequency divided by number of poles; slip is the difference between synchronous and rotor speed over synchronous speed.

Power factor correction

Capacitance per phase needed to raise power factor equals active power times the difference of tangents of the initial and target angles, divided by two pi f V squared.

Conductor colour code

Under IEC 60446 line conductors are brown, black and grey, neutral is blue, and the protective conductor is green-yellow; these colours must not be reused for other purposes.

Minimum conductor sizes

Copper lighting circuits require at least 1.5 square millimetres, socket-outlet circuits at least 2.5 square millimetres, subject to correction factors and protective device rating.

Fire-rated cable

Fire-resistant cables maintain circuit integrity for a defined period such as 30, 60 or 120 minutes and are required for fire alarm, emergency lighting and smoke control circuits.

Cable tray fill

Cable tray and conduit fill limits cap the sum of cable cross-sections, commonly 40 to 50 percent of the containment cross-section, to allow heat dissipation and later pulling.

SWA cable gland

Steel wire armoured cable requires a gland that clamps and earths the armour; the gland must match the cable type and, in hazardous areas, carry the appropriate certification.

Lockout tagout sequence

Isolate the supply, lock and tag, prove dead with a tested voltage detector, apply earths and short-circuits, guard adjacent live parts, then issue the permit to work.

Insulation resistance test voltage

Apply 500 V DC for circuits rated up to 500 V and 1000 V DC for 690 V systems; the minimum acceptable result is generally 1 megohm per circuit.

Ring circuit continuity

For a ring final circuit the resistance of the protective conductor end-to-end must not exceed the line conductor end-to-end resistance, confirming the ring is complete.

Thermographic survey

An infrared survey under load reveals loose or high-resistance connections by comparing phase-to-phase and phase-to-ambient temperature rises before failure occurs.

Initial verification sequence

IEC 60364-6 order: visual inspection, continuity, insulation resistance, polarity, earth electrode resistance, loop impedance, RCD operation and functional tests, recorded on a certificate.

RCD trip time limits

A general-type RCD must trip within 300 milliseconds at rated residual current and within 40 milliseconds at five times rated current, and must not trip at half rated current.

Fall-of-potential method

Earth electrode resistance is measured by driving two auxiliary rods at defined spacings and measuring voltage and current; the result is plotted to confirm the plateau reading.

Loop impedance correction

Measured loop impedance is compared with the tabulated maximum after applying a 0.8 correction factor to account for conductor resistance at operating temperature.

Protection relay secondary injection

Secondary injection applies known currents and voltages to relay terminals to verify pickup, timing and trip contacts against the coordination study settings before energisation.

Half-split method

Divide the circuit or signal path into two halves, test at the midpoint, then repeat on the faulty half, reducing the number of test points needed logarithmically.

Nuisance RCD tripping

Cumulative leakage from many loads, transient surges, or a genuine insulation fault can trip an RCD; insulation resistance tests and progressive disconnection separate the causes.

Motor fails to start

Check supply voltage and phase balance, control circuit, overload relay state, winding resistance and insulation, then the mechanical load, before replacing the motor.

Harmonic symptoms

Neutral current exceeding phase current, transformer overheating and distorted waveforms indicate harmonics; a power quality analyser records total harmonic distortion and spectra.

IEC 60364 protection measures

Permitted shock protection measures include automatic disconnection, double or reinforced insulation, SELV and PELV, electrical separation, and extra-low voltage with limited energy.

Ex zone classification

IEC 60079-10-1 defines gas zones 0, 1 and 2 and dust zones 20, 21 and 22; equipment group, category and temperature class must match the zone.

Test certificate contents

A test certificate records installation identification, extent and limitations, instrument serial numbers and calibration dates, results, departures, and the signature of the competent person.