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Electrical safety on site questions for the CSCS test

7 free questions on Electrical safety on site, from section C. Safety. Every question is original and explains why each option is right or wrong.

Last verified against HSE guidance and the law ·How we write our questions

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Question 1

Easier ·Link to this question (question 1)

Power tools on site run on 110 volts, from a yellow transformer.

Why is this safer than using 230 volt mains tools?

Choose one answer.

  1. A. If something goes wrong, the shock is much less likely to kill
  2. B. A 110 volt tool can't give you an electric shock at all
  3. C. It means cables never need checking before use
  4. D. It allows the tools to be used in the rain without any risk
Show the answer and explanation

Answer: A

  • A. Right: Right. A 110 volt supply that is centre-tapped to earth means no more than 55 volts between a live wire and earth. A shock is much less likely to be fatal.
  • B. Wrong: Wrong. You can still get a shock from 110 volts. It is just much less dangerous than 230 volts.
  • C. Wrong: Wrong. All cables, plugs and tools still need checking for damage before use.
  • D. Wrong: Wrong. Water still increases the risk. Battery or air tools may be better in very wet conditions.

Explanation

Use battery tools or 110 volt tools on site. A 110 volt centre-tapped supply limits any shock to 55 volts to earth.

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Question 2

Easier ·Link to this question (question 2)

Before using an extension lead, you see that a damaged part of the cable has been wrapped in insulating tape.

What should you do?

Choose one answer.

  1. A. Use it, but only for a short job
  2. B. Stop using it and report it
  3. C. Use it, as the tape covers the damaged part of the cable
  4. D. Add more tape to make it stronger
Show the answer and explanation

Answer: B

  • A. Wrong: Wrong. A faulty cable can give a shock on a short job just as easily as on a long one.
  • B. Right: Right. HSE says check that cables are not damaged and have not been repaired with insulating tape. Take it out of use and report it.
  • C. Wrong: Wrong. Tape is not a proper repair. The cable inside may still be damaged and could give a shock.
  • D. Wrong: Wrong. More tape does not make it safe. It needs a proper repair or replacing.

Explanation

Check tools, plugs and cables before use. If anything is damaged or taped up, don't use it. Report it.

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Question 3

Medium ·Link to this question (question 3)

A tipper lorry needs to drop its load near some overhead power lines that cross the site.

What should you assume about the lines?

Choose one answer.

  1. A. They are safe as long as the lorry's tyres are rubber
  2. B. They are only dangerous if the lorry actually touches them
  3. C. They are live, unless their owner has proved otherwise
  4. D. They are dead, because there are no warning signs
Show the answer and explanation

Answer: C

  • A. Wrong: Wrong. Rubber tyres do not protect you. Electricity can jump across a gap to a raised tipper body.
  • B. Wrong: Wrong. Electricity can arc across a gap, so getting close is dangerous too. That is why a safe clearance distance is set with the line owner.
  • C. Right: Right. HSE says assume overhead lines are live unless their owner proves otherwise. Work near them needs planning with the owner, plus barriers, goalposts and warning notices.
  • D. Wrong: Wrong. A lack of signs does not mean the lines are dead. Always assume they are live.

Explanation

Treat overhead lines as live. Keep plant and vehicles well clear, using barriers and goalposts, and plan any work near them with the line owner.

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Question 4

Easier ·Link to this question (question 4)

You plug a power tool into a socket that has a residual current device (RCD).

What should you do before using the tool?

Choose one answer.

  1. A. Wet your hands to see if it trips
  2. B. Unscrew the RCD and look inside
  3. C. Press the RCD's test button to check it trips
  4. D. Nothing, as an RCD makes the tool completely safe
Show the answer and explanation

Answer: C

  • A. Wrong: Wrong. Never test electrical safety on yourself.
  • B. Wrong: Wrong. Only a competent electrician should open electrical equipment.
  • C. Right: Right. HSE says the user should test a plug-in or socket RCD before use by pressing its test button.
  • D. Wrong: Wrong. HSE says an RCD is only a secondary safeguard. You still need to check the tool and cable.

Explanation

Test an RCD with its test button before use. It is a back-up safeguard, so still check the tool, plug and cable.

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Question 5

Medium ·Link to this question (question 5)

During a refurbishment, an old lighting circuit needs to be disconnected before the ceiling is taken down.

Who should do this?

Choose one answer.

  1. A. Any worker, once the light switch is turned off
  2. B. The first person to arrive on site
  3. C. Anyone wearing rubber gloves
  4. D. A trained, competent electrician
Show the answer and explanation

Answer: D

  • A. Wrong: Wrong. A switch does not isolate a circuit. Parts can still be live.
  • B. Wrong: Wrong. Only trained, competent people should work on electrical systems.
  • C. Wrong: Wrong. Rubber gloves are not a safe system of work. The circuit must be isolated by a competent person.
  • D. Right: Right. HSE says electrical work should only be done by people who are trained and competent, and safe isolation procedures must be followed at all times.

Explanation

Only trained, competent people should work on electrical systems, and they must use safe isolation. Never assume a circuit is dead.

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Question 6

Medium ·Link to this question (question 6)

Your gang has plans showing where the buried cables are on a site.

How far can you rely on the plans?

Choose one answer.

  1. A. Only as a guide; cables still need tracing on site
  2. B. Completely, as they show exactly where every cable is
  3. C. Not at all, so there is no point getting them
  4. D. Only if the plans are less than a year old
Show the answer and explanation

Answer: A

  • A. Right: Right. HSE says plans give only an indication of where services are. Cables must be traced with a locator and marked before digging.
  • B. Wrong: Wrong. Plans can be wrong or out of date, and cables move.
  • C. Wrong: Wrong. Plans are a useful starting point. They just need checking on site.
  • D. Wrong: Wrong. Even new plans only show roughly where services are.

Explanation

Service plans only show roughly where cables are. Trace and mark them with a locator, then confirm with hand-dug trial holes.

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Question 7

Easier ·Link to this question (question 7)

You are working outdoors in wet, muddy conditions and need a drill.

Which would be the safest choice?

Choose one answer.

  1. A. A drill with a cable repaired with tape
  2. B. A battery-powered drill
  3. C. A 230 volt drill plugged into the site office socket
  4. D. Any drill, as long as you wear gloves
Show the answer and explanation

Answer: B

  • A. Wrong: Wrong. A taped cable should not be used at all.
  • B. Right: Right. HSE says in damp conditions you may choose battery or air-powered tools. They remove the risk of a mains shock.
  • C. Wrong: Wrong. 230 volts in wet conditions is a serious shock risk.
  • D. Wrong: Wrong. Gloves don't make a mains tool safe in the wet.

Explanation

In wet conditions use battery or air tools, or 110 volt tools. Check tools and cables before use.

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