⚡ Electrical Safety, Plant & Equipment (PUWER)

1. What is the main reason 110V centre-tapped-to-earth (CTE) equipment is preferred over 230V equipment on a construction site?

1. It runs power tools faster and with more torque
2. If a fault occurs, the shock risk is greatly reduced
3. It removes the need to wear any protective gloves
4. It uses less electricity and saves the company money

With a 110V CTE supply the voltage to earth is limited to around 55V, so the severity of any electric shock from a fault is much lower than with 230V. Source: Electricity at Work Regulations 1989 / HSE guidance HSG141

2. On a UK construction site, what colour is the plug and connector used for a 110V power supply?

1. Blue
2. Yellow
3. Red
4. Black

By convention 110V site equipment uses yellow plugs and connectors, while blue is 230V and red is 415V three-phase. Source: BS EN 60309 / HSE guidance HSG141

3. Which type of power tool is generally regarded as the safest from an electric shock point of view?

1. 230V mains tools
2. Battery (cordless) tools
3. 415V three-phase tools
4. 110V transformer-fed tools

Battery tools carry no risk of shock from a mains supply, making them the safest option where suitable. Source: Electricity at Work Regulations 1989 / HSE guidance

4. You notice the cable on your 110V drill has a cut in its outer covering with a wire showing. What should you do?

1. Wrap insulating tape around it and carry on
2. Take it out of use, label it and report it
3. Carry on but only use it for short jobs
4. Repair the cable yourself before using it

Damaged equipment must be taken out of use and reported; unauthorised repairs and continued use both create a serious shock risk. Source: Electricity at Work Regulations 1989 / HASAWA 1974 s.7

5. Electricity can harm a worker in several ways. Which of these is a direct danger of electricity?

1. Hearing loss from noise
2. Electric shock and burns
3. Hand-arm vibration
4. Dust inhalation

The main direct dangers of electricity are shock, burns, and the fire or explosion that electrical faults can cause. Source: Electricity at Work Regulations 1989 / HSE guidance

6. You find a workmate who has collapsed and is still gripping a live electrical tool. What is the FIRST thing you should do?

1. Grab them and pull them clear straight away
2. Switch off the supply or isolate it before touching them
3. Pour water over them to cool any burns
4. Start chest compressions immediately

You must isolate the supply first; touching someone still in contact with a live source means the current can pass through you as well. Source: Electricity at Work Regulations 1989 / HSE first aid guidance

7. Who is allowed to carry out repairs to electrical equipment and installations on site?

1. Any operative who feels confident
2. Only a competent, authorised person
3. The first person to find the fault
4. Anyone wearing rubber gloves

Only competent, authorised people may work on electrical equipment; unauthorised repairs are prohibited because of the danger involved. Source: Electricity at Work Regulations 1989 reg.16

8. Before work begins on an electrical circuit that has been switched off, what must be done to confirm it is safe?

1. Wait ten minutes for it to cool down
2. Isolate it and prove it is dead
3. Check the colour of the cables
4. Ask a colleague if they switched it off

A circuit must be isolated and then proved dead with a suitable tester before work starts, as a switch alone cannot be relied upon. Source: Electricity at Work Regulations 1989 / HSE guidance GS38

9. An extension lead is running across a wet area of the site to power a 110V tool. What is the main concern?

1. The lead may get dirty and need cleaning
2. Water and damaged insulation increase the shock and fault risk
3. The tool will run more slowly in the damp
4. The colour of the lead may fade in water

Water increases the risk of electric shock and electrical faults, so leads should be kept out of wet areas and checked for damage. Source: Electricity at Work Regulations 1989 / HSE guidance HSG141

10. What does a residual current device (RCD) do to help protect against electric shock?

1. It boosts the voltage to run tools faster
2. It quickly cuts the supply if it detects a fault current
3. It stores power in case of a power cut
4. It converts 230V down to 110V

An RCD detects current leaking to earth, such as through a person, and rapidly disconnects the supply to reduce the severity of a shock. Source: Electricity at Work Regulations 1989 / HSE guidance

11. You are about to use a 110V tool and notice the RCD test button has not been pressed for some time. What is the best action?

1. Use the tool anyway as RCDs rarely fail
2. Test the RCD before use and report any fault
3. Remove the RCD to save time
4. Assume someone else has tested it today

RCDs should be tested regularly using the test button to confirm they will trip; a faulty RCD offers no protection. Source: Electricity at Work Regulations 1989 / HSE guidance HSG141

12. Why can an electrical fault lead to a fire on site?

1. Electricity makes materials damp
2. Overheating, arcing or sparks can ignite nearby materials
3. Electric current cools surfaces too quickly
4. Cables absorb oxygen from the air

Faults such as overloading, short circuits and arcing generate heat and sparks that can ignite combustible materials, providing the heat for the fire triangle. Source: Regulatory Reform (Fire Safety) Order 2005 / HSE guidance

13. A small fire has started in an electrical distribution board. Which extinguisher is suitable for use on live electrical equipment?

1. Water extinguisher
2. CO2 (carbon dioxide) extinguisher
3. Foam extinguisher
4. Wet chemical extinguisher

CO2 extinguishers are safe on live electrical equipment because the agent does not conduct electricity; water and foam can cause a shock. Source: Regulatory Reform (Fire Safety) Order 2005 / HSE guidance

14. In which type of work area could an electrical spark be especially dangerous because it could cause an explosion?

1. An open, well-ventilated yard
2. An area where flammable gases or vapours are present
3. A clean office with no machinery
4. A car park during dry weather

Where flammable gases, vapours or dusts are present, even a small electrical spark can ignite the atmosphere and cause an explosion. Source: DSEAR 2002 / HSE guidance

15. What is the purpose of the centre-tapped-to-earth design of a 110V site transformer?

1. To double the available power output
2. To limit the voltage between any live conductor and earth to about 55V
3. To allow the use of thinner, cheaper cables
4. To make the tools completely waterproof

Centre-tapping to earth splits the 110V so that the voltage to earth is around 55V, significantly reducing the severity of a shock if a fault occurs. Source: Electricity at Work Regulations 1989 / HSE guidance HSG141

16. Portable electrical equipment on site should be subject to a combination of user checks and formal inspection. What is the user's role before each use?

1. Carry out a full electrical test with a meter
2. Visually check leads, plugs and casing for damage
3. Open the casing to inspect internal wiring
4. Re-fuse the plug to the correct rating

Users should make a visual check for obvious damage before use; detailed testing is for competent persons under a planned inspection regime. Source: Electricity at Work Regulations 1989 / HSE guidance INDG236

17. Why can even a relatively low electric shock be dangerous when working at height?

1. It always causes permanent paralysis
2. The shock or muscle reaction can cause a fall
3. It increases the voltage of nearby tools
4. It makes harnesses conduct electricity

A shock can cause an involuntary reaction or loss of grip, leading to a fall from height even if the shock itself is not fatal. Source: Electricity at Work Regulations 1989 / Work at Height Regulations 2005

18. What does a cable avoidance tool (CAT) help you to do before digging?

1. Measure the depth of the excavation
2. Detect buried cables and metal services
3. Test the strength of the soil
4. Check the level of the ground

A CAT is used to locate buried cables and other metallic or signal-carrying services so they can be avoided when digging. Source: HSE guidance HSG47 (Avoiding danger from underground services)

19. What colour are buried electricity cables usually marked with in the UK?

1. Blue
2. Black or red
3. Yellow
4. Green

Buried electricity cables are traditionally black or red, though many newer ones are coloured to standard schemes; colour alone should never be relied upon. Source: HSE guidance HSG47

20. Before any digging begins on site, what should you obtain to help locate buried services?

1. A weather forecast for the week
2. Drawings or plans of underground services
3. A list of tools on site
4. The site manager's phone number

Service drawings and utility plans should be obtained and used alongside a CAT to locate buried services before digging. Source: HSE guidance HSG47

21. What is used together with a CAT to locate a specific buried cable or pipe more accurately?

1. A signal generator (genny)
2. A spirit level
3. A tape measure
4. A hammer

A signal generator, often called a genny, applies a traceable signal to a service so the CAT can follow its exact route. Source: HSE guidance HSG47

22. You are working near an overhead power line. What is the safest way to reduce the risk of contact?

1. Work as quickly as possible underneath it
2. Establish exclusion zones and barriers, and avoid the line
3. Touch the line to see if it is live
4. Move the line yourself out of the way

Goal posts, barriers and exclusion zones keep plant and people a safe distance from overhead lines, which should never be touched. Source: HSE guidance GS6 (Avoiding danger from overhead power lines)

23. When digging near where a CAT has indicated a buried cable, how should you complete the excavation around it?

1. Use a mechanical excavator at full speed
2. Dig carefully by hand using safe digging practices
3. Use a pneumatic breaker directly over the cable
4. Pour water in to wash the soil away from the cable

Once a service is located, careful hand digging is used to expose it, as mechanical tools could strike and damage the cable. Source: HSE guidance HSG47

24. How often should a cable avoidance tool (CAT) be checked to make sure it works correctly?

1. Once a year only
2. Regularly, including a check before each use
3. Only when it stops working
4. Never, as they do not fail

A CAT should be checked before use and calibrated periodically, because a faulty CAT may fail to detect a cable and give a false sense of safety. Source: HSE guidance HSG47

25. While excavating, you strike and damage a buried electricity cable but no one is hurt. What should you do?

1. Cover it back over and say nothing
2. Stop work, keep clear and report it immediately
3. Try to tape the cable back together
4. Carry on digging carefully around it

You must stop, keep people clear of the damaged cable and report it at once, as a struck cable can still be live and dangerous. Source: HSE guidance HSG47 / RIDDOR 2013

26. Why should you not rely only on the indicated depth of a buried cable shown on a plan?

1. Plans are always perfectly accurate
2. Cables may have moved, been re-laid, or the ground level changed
3. Cables become shallower in summer
4. Depth has no effect on safety

Recorded depths can be wrong because ground levels change and services are sometimes re-laid, so plans must be combined with a CAT and safe digging. Source: HSE guidance HSG47

27. A mobile crane must operate close to overhead power lines that cannot be diverted or switched off. What control is most appropriate?

1. Rely on the operator to judge the distance by eye
2. Set up barriers and goal posts to define a safe clearance and exclusion zone
3. Remove the crane's load limiter to give more reach
4. Work only on dry days so the line is safe to touch

Where lines cannot be removed or isolated, physical barriers, goal posts and defined exclusion zones keep plant a safe distance away. Source: HSE guidance GS6

28. A CAT used in power mode detects a buried live cable by sensing what?

1. The heat given off by the cable
2. The electromagnetic field around the live cable
3. The colour of the cable through the soil
4. The smell of the cable insulation

In power mode a CAT detects the electromagnetic field radiated by a live cable carrying current; this is why it may miss a cable that is not loaded. Source: HSE guidance HSG47

29. What is the preferred voltage for portable electric hand tools used on a construction site?

1. 230 V mains supply
2. 110 V reduced low voltage
3. 400 V three-phase supply
4. 12 V supply only

On site, 110 V reduced low voltage is preferred over 230 V because it greatly reduces the severity of any electric shock. Source: Electricity at Work Regulations 1989 / HSE guidance

30. On a construction site, what colour is the plug and connector for a 110 V tool?

1. Blue
2. Yellow
3. Red
4. Black

110 V site equipment uses yellow plugs and connectors, helping workers identify the safer reduced low voltage supply at a glance. Source: HSE guidance / BS EN 60309

31. Which type of power tool is generally considered the safest to use from an electric shock point of view?

1. A 230 V tool with a long extension lead
2. A battery (cordless) tool
3. A 110 V tool with a damaged casing
4. A 400 V three-phase tool

Battery-powered (cordless) tools are the safest option because they operate at low voltage and are not connected to a mains supply. Source: Electricity at Work Regulations 1989 / HSE guidance

32. What device is used to reduce a 230 V supply down to 110 V for site tools?

1. A residual current device (RCD)
2. A step-down (110 V) transformer
3. A circuit breaker
4. An extension reel

A step-down transformer reduces the mains 230 V supply to the 110 V reduced low voltage used by site tools. Source: HSE guidance

33. You notice the cable on a 110 V drill has a deep cut exposing the inner wires. What should you do?

1. Wrap insulating tape around it and carry on
2. Take the tool out of use and report it
3. Use it only for short tasks
4. Repair the cable yourself with a connector

A damaged cable must be taken out of use and reported; you must never carry out unauthorised repairs. Source: Electricity at Work Regulations 1989 / HSE guidance

34. On a 110 V centre-tapped-to-earth (CTE) system, what is the main safety benefit?

1. Tools run faster
2. The voltage to earth is halved to around 55 V, reducing shock severity
3. No transformer is needed
4. It removes the need for any earthing

With a centre-tapped-to-earth 110 V supply the voltage to earth is limited to around 55 V, which significantly reduces the severity of an electric shock. Source: HSE guidance / Electricity at Work Regulations 1989

35. Before using a portable electric tool, what should you always do first?

1. Test it on full power
2. Carry out a quick visual check of the tool, lead and plug
3. Remove the guard to check the blade
4. Plug it in and leave it running for a minute

A user pre-use visual check of the tool, cable and plug helps spot obvious damage before the tool is energised. Source: HSE guidance (Provision and Use of Work Equipment Regulations 1998)