Electrical Safety

What is the primary hazard of electricity?

• AEye strain from flickering fluorescent lighting
• BElectric shock causing injury or death✓
• CThe noise made by the electrical equipment
• DTrip hazards from trailing extension leads

Answer: Electric shock is the primary hazard. Electricity can cause cardiac arrhythmia, respiratory paralysis, burns, and death. Even low voltages can be lethal under certain conditions.

What is the significance of the 50 V AC 'safe voltage limit' in the UK?

• AAbove 50V AC becomes hazardous; lower voltages are safer but not necessarily safe✓
• B50 V AC is the UK domestic mains voltage
• CAnything below 50V is safe
• DThe level above which BS 7671 requires cables to be armoured throughout

Answer: 50 V AC is the upper limit of extra-low voltage in BS 7671 and is widely used as a threshold for shock risk. Lower voltages are safer, but they can still cause a harmful shock in wet conditions, with a large contact area or for a vulnerable person, so a voltage below 50 V is not automatically safe. UK mains is 230 V AC.

What are the main routes of electrical current entry to the body?

• AInduction through the air from cables running within a metre of the body
• BContact with live parts; hand-to-hand, hand-to-foot, or foot-to-foot paths✓
• CEarth-to-earth paths between two bonded metal parts at the same potential
• DFoot-to-foot, which is the path most likely to pass current through the heart

Answer: Current enters through contact with live parts, with dangerous paths including: hand-to-hand (across the chest, affecting heart), hand-to-foot, and foot-to-foot paths.

What is an 'arc flash'?

• AA regular spark
• BLightning in the sky during a storm, which can travel down a supply cable into a building on site
• CA safety device
• DDangerous electrical event with intense heat and light from arcing between live conductors✓

Answer: Arc flash is a dangerous electrical event where current jumps across a gap (arc), producing intense heat (>3000°C), light, pressure, and hot metal spray that can cause severe burns.

What does 'earthing' do in an electrical system?

• AIt is what makes the electricity flow round the whole of the final circuit
• BIt is only there to give lightning a path to earth during a thunderstorm
• CProvides a return path for fault current and reduces electric shock risk✓
• DIt reduces the voltage supplied to the final circuits

Answer: Earthing (grounding) provides a safe path for fault currents to earth, reducing the voltage experienced by a person in contact with an energised object.

What is 'double insulation' in electrical equipment?

• AUsing two plugs so that the equipment always has a spare supply
• BTwo layers of insulation preventing contact with live parts✓
• CTwo complete sets of wires running to the same piece of equipment
• DExtra heavy cables fitted with a thicker outer sheath than normal

Answer: Double insulation provides two independent layers of insulation (functional and protective) so that if one breaks down, the second prevents contact with live parts.

What is a Residual Current Device (RCD)?

• AA safety device that detects current imbalance and disconnects the circuit quickly✓
• BA resistor
• CA type of wire with a larger cross-section, used where the circuit carries a heavy load
• DAn insulator

Answer: An RCD (earth leakage breaker) detects any imbalance between live and neutral currents (indicating current to earth) and trips the circuit within milliseconds, preventing serious shock.

What is BS 7671?

• AThe IET Wiring Regulations - UK standard for safe electrical installation design and installation✓
• BAn electrical component fitted inside a consumer unit, which the manufacturer supplies with its own instructions
• CA cable type
• DA voltage rating

Answer: BS 7671:2018 (Requirements for Electrical Installations) is the UK standard for the design, selection, installation, inspection and testing of electrical systems.

What does 'isolation' mean in electrical safety?

• ASwitching the equipment off at the local switch and leaving a note on it to say that work is in progress
• BUnplugging a device
• CSeparating equipment from live parts by creating a physical barrier or disconnecting from supply✓
• DTurning off the lights

Answer: Isolation is the safe separation of electrical equipment from all live parts by physical isolation (barriers, covers) and/or electrical isolation (disconnection from the supply).

What is 'lock off tag out' (LOTO)?

• AProcedure of isolating equipment and preventing accidental energisation by locking disconnects and applying warning tags✓
• BOnly for padlocks
• CJust a label
• DLocking tools and equipment away in the site store at the end of the shift so that nobody can use them overnight without permission

Answer: LOTO involves isolating equipment from energy sources and using physical locks and warning tags to prevent unexpected startup while work is being carried out.

What should be done before working on electrical equipment?

• AAsk the person who fitted the equipment whether it is safe, and take their word for it
• BOnly if in a hurry
• CJust dive in
• DIsolate from supply, lock off, test the circuit is de-energised, use appropriate PPE✓

Answer: Safe procedure: Isolate the equipment, lock and tag the isolator, test with a voltage tester to confirm de-energisation, and only then proceed with work using proper PPE.

What is a 'live working permit'?

• ADiscretionary
• BAny written authorisation to start work, whether the equipment is live or has been isolated
• CFormal authorization to work on energized electrical equipment under strict procedures✓
• DA driving license

Answer: A live working permit formally authorizes and documents work on live electrical parts, requiring competent personnel, additional controls, and strict procedures to minimize shock risk.

What is the correct way to test that a circuit is de-energised?

• ATouch the conductors with the back of your finger to feel for a tingle
• BSwitch the breaker off and rely on the label at the board
• CUse a proper voltage tester/multimeter to confirm no voltage present✓
• DAsk the person who isolated it whether it is safe to touch the conductors

Answer: Always use a properly functioning voltage tester or multimeter to confirm absence of voltage. Test the tester first on a known energised source to verify it works.

What is 'overhead line clearance' distance?

• AMinimum safe distance to keep from overhead power lines as agreed with the line owner✓
• BThe height by which the line sags at the midpoint between two poles
• CThe time allowed for a tripped line to reclose before work resumes
• DThe spacing between the phase conductors needed to stop them clashing in wind

Answer: Overhead power lines have minimum clearance distances to prevent electrocution, including by flashover. HSE advises getting the safe clearance from the line owner, and GS6 says to manage the risk for any work within 10 m of the nearest wire, with barriers usually set 6 m either side of the line.

What hazards exist when working on electrical distribution boards?

• AThere are no hazards once the main switch on the board has been turned off
• BHeat, noise and the weight of the board when it is being removed
• COnly the noise made by the contactors and breakers inside the board
• DElectric shock, arc flash, confined space hazards if in enclosures✓

Answer: Distribution boards present risks of shock from live parts, arc flash if a fault occurs, and potentially confined space hazards. Proper PPE and isolation procedures are essential.

What is the purpose of an 'insulated tool' in electrical work?

• AIt serves no particular purpose beyond comfort in the hand when working
• BIt just feels better in the hand than a standard uninsulated tool
• CTo reduce shock risk by preventing current path through the body✓
• DTo make the work go faster by improving the grip on the fixings used

Answer: Insulated tools provide a barrier between the worker and live parts, reducing the risk of electric shock if the tool contacts a live conductor accidentally.

What is 'temporary bonding' in electrical safety?

• AUnimportant
• BJust decorative wiring
• CUsing temporary wires to feed power to tools while the permanent supply is being installed
• DTemporary connection of conductive parts to ensure they are at the same potential✓

Answer: Temporary bonding electrically connects exposed conductive parts to the same potential, preventing dangerous potential differences and arcing between parts.

What should you do if someone receives an electric shock?

• APull them away from the equipment immediately with your bare hands before anything else
• BSwitch off supply first if safe, then provide first aid, call emergency services✓
• CPull them clear by the arm, then check whether they are breathing
• DLeave the casualty where they are and go off site to find help for yourself first

Answer: On discovering an electrical shock victim: switch off the supply (if safe), or break contact using non-conducting material, provide CPR/first aid, and call emergency services.

What is a 'permit to work' system for electrical work?

• ADispensable
• BFormal authorisation system documenting risk assessment, isolation steps, and precautions for work on electrical equipment✓
• CJust a verbal agreement between the electrician and the supervisor that the work can go ahead, recorded in the site diary afterwards
• DPermission slip from home

Answer: A permit to work for electrical tasks documents: identified hazards, isolation measures, lock-off procedures, testing confirmation, rescue arrangements, and authorised personnel.

What is an 'electrical test certificate'?

• AA qualification
• BA diploma
• CDocumentation confirming that electrical installation or equipment has been properly tested and meets safety standards✓
• DJust a piece of paper handed over at the end of the job, with no legal or technical meaning attached to it at all whatsoever

Answer: An electrical test certificate documents the results of periodic inspection and testing of electrical installations, confirming safety standards are met and no faults exist.

What is 'earth fault loop impedance' (EFLI)?

• AA transformer fitted at the origin of the installation to reduce the supply voltage before it reaches the circuits
• BA test of insulation resistance, made between live conductors and earth
• CThe maximum current that a protective device will carry
• DThe impedance of the path for earth fault current, affecting shock protection effectiveness✓

Answer: EFLI is the total impedance in the earth fault path, measured during testing. Lower EFLI means faster fault clearance and better protection against electric shock.

What protection is provided by a circuit breaker?

• ADiverts lightning surges to earth, protecting equipment from overvoltage
• BAutomatically disconnects supply when current exceeds safe levels, preventing overheating and fire✓
• CHolds the voltage steady at 230 V when the supply dips or rises during use
• DActs as a manual isolator for maintenance and has no automatic tripping function

Answer: Circuit breakers automatically disconnect the circuit if current exceeds design limits, protecting against overcurrent, short circuits, and the resulting overheating and fire risk.

What is 'competency' for electrical work?

• ALuck and quick thinking
• BHaving adequate knowledge, skills, training, and experience to work safely with electricity✓
• CHaving finished enough electrical jobs to be quick at the work, whatever training has been done
• DJust having a tool kit

Answer: Electrical competence requires: relevant qualifications, training in safety procedures, understanding of BS 7671, experience with similar work, and demonstrated practical ability.

What should be included in an electrical safety briefing for workers?

• AHazards, safe procedures, isolation requirements, emergency arrangements, and specific work precautions✓
• BThe company's history, organisation chart and holiday booking procedures
• CA general reminder to take care, with the detail left to each worker
• DSales targets and the programme for the next phase of works

Answer: A briefing should cover: specific hazards of the task, required safety procedures, isolation and lock-off arrangements, emergency procedures, and rescue arrangements.

What is 'thermal burn' in the context of electrical injury?

• ABurn caused by heat from electrical current or arc flash✓
• BSunburn picked up while working outdoors on a hot summer day
• CA minor injury that is not dangerous and needs no treatment
• DA burn that can only be caused by open flames or hot surfaces

Answer: Thermal burns result from the heat generated by electrical current passing through tissue or from arc flash. They can be severe and deep, causing tissue damage.