Earthing, Safety and Pakistan Grid Practices MCQs 2026

Safety tagging on isolated NTDC circuits uses

1. Agreen tag meaning energize✓
2. Bno documentation✓
3. Ctags on unrelated feeders only✓
4. Ddanger tags and earth tags after proven dead and earthed✓

Grid frequency in Pakistan is nominally

1. A60 Hz always without exception✓
2. B25 Hz for all transmission✓
3. C400 Hz for distribution✓
4. D50 Hz with operational limits per grid code✓

Working near exposed busbars in substation requires

1. Aconductive jewelry for convenience✓
2. Bwet cotton gloves only✓
3. Carc-rated clothing and insulated tools per hazard assessment✓
4. Dno barricades ever✓

Consumer earthing inspection under distribution safety rules checks

1. Aonly decorative wiring✓
2. Bonly highest lamp wattage✓
3. Conly motor paint color✓
4. Dearth electrode resistance, bonding and RCD operation✓

Reporting of major grid disturbances to regulator supports

1. Areliability monitoring and corrective investment under NEPRA framework✓
2. Bonly internal memo without data✓
3. Cdeletion of event records✓
4. Dno protection review✓

Live-line maintenance on transmission requires

1. Aany worker without PPE✓
2. Bshorting phase to earth without permit✓
3. Cignoring weather limits always✓
4. Dtrained crews, approved tools and safety distances per utility procedure✓

Neutral earthing in transmission is often through

1. Afloating without any monitoring✓
2. Bdirect connection to street lighting circuit✓
3. Conly ELCB at 30 mA on EHV bus✓
4. Dsubstation transformer neutral reactor/resistor or solid ground per study✓

Distributed generator connecting to grid must meet NEPRA/NTDC requirements for

1. Auncontrolled energization during outage✓
2. Bno circuit breaker at POI✓
3. Canti-islanding, protection, metering and power quality✓
4. Dreverse power flow without study✓

Incident energy study for NTDC/DISCO switchgear supports

1. Aonly lamp maintenance factor✓
2. Bselection of arc-flash PPE and safe working distances✓
3. Conly motor slip calculation✓
4. Donly cable charging MVAR✓

Earthing of NTDC substation structures and equipment follows

1. Aonly single 1 ohm rod without study✓
2. Bengineered earth grid design for fault current and touch/step limits✓
3. Cfloating earth without reference✓
4. Dconnection to phase conductor✓

Protection coordination on NTDC grid ensures

1. Aall breakers trip on any fault simultaneously always✓
2. Bno relay settings ever changed✓
3. Cfault cleared by nearest breaker with backup discrimination✓
4. Donly fuse protection on 500 kV✓

Authorization to work on NTDC substation equipment requires

1. Aonly verbal agreement✓
2. Bdirect energization for test without lockout✓
3. Cpermit-to-work and isolation with earth application procedures✓
4. Dbypassing interlocks routinely✓

Safety clearance from live overhead lines for workers is governed by

1. Aonly luminaire spacing tables✓
2. BNTDC/utility safety rules and IE Rules aligned practices✓
3. Conly motor nameplate only✓
4. Donly cable color mnemonic✓

Permissible voltage variation at consumer terminals in many standards is approximately

1. A±6% or as per applicable regulation✓
2. B±50% without limit✓
3. Cexactly 0% always✓
4. D±30% for all loads✓

Grid Code issued under NEPRA framework defines

1. Atechnical and safety requirements for grid-connected parties✓
2. Bonly color of insulators without electrical limits✓
3. Conly welding electrode sizes✓
4. Donly lamp CRI values✓

NTDC operates

1. Aonly domestic house wiring✓
2. Bonly diesel generator retail sales✓
3. Conly street lighting design✓
4. Dnational transmission grid and bulk power dispatch in Pakistan✓

NEPRA in Pakistan regulates

1. Aonly telecommunications spectrum✓
2. Bonly water supply tariffs✓
3. Celectric power sector including licensing and consumer protection standards✓
4. Donly aviation fuel pricing✓

Periodic inspection of RCD includes

1. Atrip time test at rated residual current per IEC 61557✓
2. Bonly painting enclosure✓
3. Conly tightening lamp holder✓
4. Donly measuring lux level✓

Fire protection RCDs may be rated

1. A300 mA with time delay for discrimination✓
2. B30 mA on entire factory incomer without grading✓
3. C3 A residual only✓
4. Dwithout any earthing✓

RCD rated residual operating current IΔn is

1. Athe load current rating In only✓
2. Bthe leakage current at which the device must trip✓
3. Cthe breaking capacity in kA only✓
4. Dthe lamp lumen output✓

In TT installations RCD is often mandatory because

1. Aearth resistance is always zero✓
2. Bearth fault loop impedance may be too high for fast MCB disconnection✓
3. Cneutral is solidly earthed at consumer✓
4. Dno touch voltage can exist✓

ELCB/RCD must be connected such that

1. Aneutral bypasses sensor always✓
2. Bearth wire carries load current intentionally✓
3. Call live conductors pass through the toroidal sensor✓
4. Dphase is left out of sensor✓

Type AC RCD is suitable for

1. Apure DC leakage only without AC component✓
2. Bhigh-frequency PWM without Type A/B consideration✓
3. Csinusoidal AC residual currents✓
4. Donly lightning impulse without evaluation✓

30 mA RCD may not detect

1. Aline-to-line fault if no earth path involved (unlikely on earthed systems)✓
2. Bline-to-earth fault through person✓
3. Cleakage via damaged cable to wet floor✓
4. Dappliance frame fault to PE✓

IEC 60439 / modern switchgear may use RCBO which combines

1. Aovercurrent protection and residual current protection in one device✓
2. Bonly lighting dimmer✓
3. Conly surge arrester without MCB✓
4. Donly ammeter shunt✓

RCD test button creates

1. Apermanent short of phase to neutral for load✓
2. Bsimulated imbalance to verify mechanical trip function✓
3. Copen-circuit of earth electrode✓
4. Dincrease of supply voltage to 440 V✓

Selective (time-graded) RCD coordination uses

1. Aall 30 mA instant on main incomer only✓
2. Bno earthing on sub-circuits✓
3. Chigher sensitivity downstream and delayed upstream devices✓
4. Donly fuse without any RCD✓

RCD nuisance tripping may be caused by

1. Aperfect insulation with zero leakage always✓
2. Bunity power factor alone✓
3. Ccorrect TN-S wiring only✓
4. Dcumulative leakage from filters, capacitors and damp equipment✓

Voltage-operated ELCB is largely superseded because

1. Ait is always faster than 1 ms✓
2. Bit depends on rise of earth voltage and may be less reliable✓
3. Cit eliminates need for earthing✓
4. Dit measures only DC traction current✓

RCD does not replace

1. Aovercurrent protection (MCB/fuse) for short circuit and overload✓
2. Bneed for earthing✓
3. Cinsulation on conductors✓
4. Dcorrect wiring polarity checks✓

Standard residential RCD sensitivity is often

1. A300 A✓
2. B30 A✓
3. C30 mA for additional protection against shock✓
4. D3 A✓

Residual Current Device (RCD) operates when

1. Aload power factor is unity only✓
2. Bvoltage is exactly 230 V✓
3. Cmotor is underloaded✓
4. Dvector sum of line currents deviates from zero (leakage to earth)✓

Earth Leakage Circuit Breaker (ELCB) detects

1. Aonly overvoltage on lighting circuit✓
2. Bimbalance indicating leakage current to earth✓
3. Conly motor rpm✓
4. Donly transformer flux density✓

Minimum size of main earthing conductor in many codes depends on

1. Aonly lamp wattage✓
2. Blargest incoming service conductor and fault level✓
3. Conly motor color code✓
4. Donly cable brand name✓

Lightning protection earth should be

1. Aalways completely isolated without bonding rules✓
2. Bconnected only to phase conductor✓
3. Cbonded to power system earth where codes permit common electrode✓
4. Dleft unconnected intentionally✓

Earth mat in substations is provided to

1. Alimit step and touch potentials during grid faults✓
2. Bincrease fault current path impedance only✓
3. Cdecorate switchyard only✓
4. Dreplace insulation coordination✓

Chemical earthing (maintenance-free) uses

1. Aonly dry sand without metal✓
2. Bconductive compounds around electrode to lower contact resistance✓
3. Conly insulating varnish on rod✓
4. Donly neon lamp gas✓

Step potential hazard near earth electrode during fault is

1. Avoltage across lamp filament only✓
2. Bflux in transformer core only✓
3. Cvoltage difference between feet at different soil potentials✓
4. Dpower factor of motor only✓

TN-C-S (PME) combines neutral and earth on supply side with

1. Aseparate PE after split at consumer service✓
2. Bpermanent combined PEN to all sockets without split✓
3. Cno earthing at transformer✓
4. Donly DC traction return✓

TT system earthing has

1. Ano earth electrode at all✓
2. Bphase and neutral shorted at load✓
3. Conly IT system without any earth✓
4. Dlocal earth electrode at consumer with utility neutral earthed separately✓

Separate protective earth (PE) and neutral (N) must not be

1. Acombined after the main earthing terminal except as defined by TN-S rules✓
2. Bbonded at every socket always incorrectly✓
3. Cleft floating on consumer side✓
4. Dconnected only to phase✓

Ring earth electrode around building in IEC practice provides

1. Amore uniform earth potential and lower resistance✓
2. Bhigher touch voltage always✓
3. Cno connection to main earthing terminal✓
4. Donly lightning without power earthing✓

Measurement of earth resistance commonly uses

1. Aonly voltmeter across open circuit✓
2. Bfall-of-potential (three-point) method✓
3. Conly wattmeter on lighting load✓
4. Donly oscilloscope on communication line✓

Soil resistivity affects earth electrode resistance such that

1. Aresistivity has no effect✓
2. Bdry rocky soil always gives lowest R✓
3. Conly pipe length color matters✓
4. Dhigher resistivity soil gives higher electrode resistance✓

Earth continuity conductor (ECC) ensures

1. Aphase voltage appears on casing✓
2. Bmetallic enclosures remain at earth potential during faults✓
3. Cneutral is never connected✓
4. Dfuses never blow✓

IS/IEC practice requires main equipotential bonding to connect

1. Aonly lighting switches✓
2. Bincoming metal services and structural metal to earth terminal✓
3. Conly decorative paint✓
4. Donly plastic pipes without metal✓

Plate earth electrode uses

1. Aonly overhead conductor✓
2. Bonly fluorescent lamp ballast✓
3. Cburied metal plate (GI or copper) in a pit with alternating layers of coke and salt✓
4. Donly transformer oil only✓

Pipe earth electrode is commonly made of

1. APVC conduit only✓
2. Bwooden pole only✓
3. Cair gap only✓
4. Dgalvanized iron or copper pipe driven vertically into soil✓

Earth electrode resistance should generally be

1. Aas high as possible✓
2. Bequal to load resistance✓
3. Cinfinite for safety✓
4. Das low as practicable per national code (often ≤1–5 Ω for small installations)✓

Purpose of electrical earthing in installations is primarily to

1. Aprovide a low-impedance path for fault current and limit touch voltage✓
2. Bincrease line voltage for efficiency✓
3. Celiminate need for overcurrent protection✓
4. Dstore energy in soil✓