CSCS Electrical Safety Questions
Safe voltages, cables, tools and overhead/underground power.
These questions cover electrical safety for the CITB Health, Safety and Environment (HS&E) test, the exam UK construction workers pass to get a CSCS card.
Electrical Safety: practice quiz
- 20 questions · 30 minutes · pass mark 90%
- Answers and explanations are shown at the end, with every question to review.
- A fresh 20 questions every time, drawn from all 130 in this topic's bank. Includes 2 select-two questions and 2 picture questions, as in the real test.
- About 90 seconds a question, against about 54 in the real test, so there is time to think.
10 sample Electrical Safety questions and answers
These 10 come from the 130 questions the practice quiz above draws from, written out with the correct answer and the reasoning behind it. Read them through when you want to revise rather than test yourself.
1. Under regulation 4(1), how must all electrical systems be constructed?
Answer: So as to prevent danger, so far as is reasonably practicable, at all times
- A) So as to prevent danger, so far as is reasonably practicable, at all times (correct answer)
- B) So that they can be dismantled quickly by any operative on the work site
- C) So that they carry a current rating stamped clearly on the outer casing
- D) So that they are inspected by the enforcing authority before being used
Why: Regulation 4(1) sets a continuing duty: all systems shall at all times be of such construction as to prevent, so far as is reasonably practicable, danger.
2. What is the first condition in regulation 14 for working on a live conductor?
Answer: That it is unreasonable in all the circumstances for it to be dead
- A) That the worker holds a current electrical competence card for the work
- B) That it is unreasonable in all the circumstances for it to be dead (correct answer)
- C) That the supply cannot physically be isolated from the equipment
- D) That the client has given written permission for the work to proceed
Why: Regulation 14(a) is the starting point: live working is only contemplated where it is unreasonable in all the circumstances for the conductor to be dead. Convenience is not the test.
3. What is the risk that regulation 13 is designed to prevent?
Answer: That equipment made dead becomes charged again while work continues
- A) That the equipment is damaged by the work being carried out on it
- B) That the work takes longer than the time allowed in the programme
- C) That equipment made dead becomes charged again while work continues (correct answer)
- D) That the wrong equipment is worked on because circuits are unmarked
Why: Regulation 13 is aimed squarely at re-energisation during the work, which is why locking off and proving dead matter as much as switching off.
4. Which statement about the Electricity at Work Regulations is correct?
Answer: They are goal-setting, requiring danger to be prevented by any suitable means
- A) They set specific voltages and equipment types that must be used
- B) They are goal-setting, requiring danger to be prevented by any suitable means (correct answer)
- C) They apply only to permanent installations and not to temporary site supplies
- D) They apply only to work carried out by qualified electrical contractors
Why: The Regulations repeatedly use the formula prevent danger so far as is reasonably practicable, leaving the technical means to standards and good practice.
5. What does regulation 5 of the Electricity at Work Regulations 1989 prohibit?
Answer: Putting equipment into use where its strength and capability may be exceeded so as to give rise to danger
- A) Using equipment that has not been tested and labelled within the last twelve months by a qualified electrician
- B) Putting equipment into use before it has been labelled by an electrician as tested and fit for service
- C) Putting equipment into use where its strength and capability may be exceeded so as to give rise to danger (correct answer)
- D) Using an item of electrical equipment that is more than ten years old, even if it is sound and correctly rated
Why: Regulation 5 says no electrical equipment shall be put into use where its strength and capability may be exceeded in such a way as may give rise to danger.
6. Within what distance of an overhead line does GS6 say you should manage the risks of your work?
Answer: 10 m, measured horizontally at ground level from below the nearest wire
- A) 50 m, measured from the nearest pylon or pole carrying the line
- B) Directly underneath the wires, and not to either side of them
- C) 10 m, measured horizontally at ground level from below the nearest wire (correct answer)
- D) 1 m, measured from the nearest wire in a straight line through the air
Why: GS6 paragraph 11 says you should manage the risks if you intend to work within 10 m, measured at ground level horizontally from below the nearest wire.
7. An overhead line has been damaged and appears dead. Why does GS6 say you must still treat it as live?
Answer: It can be switched back on automatically after a few seconds, or remotely later
- A) Dead lines stay charged for at least 24 hours after any fault, so treat it as live until then
- B) The line owner is legally barred from switching damaged lines off
- C) A dead line becomes live again as soon as it touches wet ground
- D) It can be switched back on automatically after a few seconds, or remotely later (correct answer)
Why: GS6 paragraph 31 says remember that even if lines are dead, they may be switched back on automatically after a few seconds or remotely after minutes or hours if the owner does not know the line is damaged.
8. You find what you think is an unsafe electrical installation on site. What does HSE say to do first?
Answer: Warn everyone to stay away from it and, if it is safe to do so, switch it off
- A) Take the cover off to find the fault, then try to repair it yourself before anyone else uses it
- B) Leave it alone and say nothing, as it is not your responsibility
- C) Wrap the exposed parts in tape and carry on using the supply
- D) Warn everyone to stay away from it and, if it is safe to do so, switch it off (correct answer)
Why: HSE's electricity FAQ says first warn everyone to stay away from it and, if safe to do so, switch it off, then contact a competent person.
9. Which fault does HSE say cannot be found by a visual inspection alone and needs a combined inspection and test?
Answer: A broken earth wire inside a flexible cable
- A) A broken earth wire inside a flexible cable (correct answer)
- B) A plug casing that is cracked across one side
- C) A cable with cuts in the sheath
- D) Burn marks on the plug
Why: HSG107 paragraph 47 says some faults, such as loss of earth integrity (for example a broken earth wire within a flexible cable), cannot be detected by visual examination alone and need a combined inspection and test.
10. Several electricians are working on the same isolated equipment. What does HSE recommend?
Answer: A multiple locking hasp, with each person applying their own lock and keeping the key
- A) A multiple locking hasp, with each person applying their own lock and keeping the key (correct answer)
- B) One padlock fitted by the supervisor, who keeps the only key on behalf of everyone working
- C) A sign on the switch listing the names of all the people working
- D) No lock at all, as long as they all agree to tell each other when they finish
Why: HSG85 paragraph 51 says where several people work, a multiple locking hasp, lock-out box or key-safe may be appropriate, with everyone applying a lock and keeping personal possession of the key.
What this topic covers in the CSCS test
Electricity gives no warning. As HSE puts it, unlike most other hazards you cannot see, feel, hear or smell it. About three workers are electrocuted each year during refurbishment work on buildings, and more die in incidents involving overhead lines and buried cables. The test sticks to what an operative controls: site voltage, RCDs, and checking a tool before you plug it in.
- Why site tools run at 110V from a transformer centre tapped to earth
- The plug and connector colour convention on UK sites
- What an RCD does, its tripping current, and how to test it
- Pre-use visual checks, and how often 110V and 230V equipment is inspected and tested
- Reporting and labelling defective tools, and why makeshift repairs are banned
- Double insulation, battery tools and safe use of extension reels
- Working near overhead power lines and buried cables
Key facts worth memorising
- 110V centre tapped to earth
- HSE says use cordless tools, or tools running from a 110V centre tapped to earth supply so the maximum voltage to earth does not exceed 55V.
- Yellow means 110V
- Site plugs and connectors are yellow for 110V and blue for 230V. The colour code is set by the industrial connector standard (BS EN 60309-2), not by HSE, but it is universal on UK sites.
- An RCD should trip at no more than 30 mA
- HSE gives 30 milliamps as the maximum tripping current for protecting people, and says to press the test button before use to confirm the mechanism works.
- Check intervals differ by voltage
- On construction sites HSE suggests a user check weekly for 110V and every shift for 230V, with a combined inspection and test before first use then three monthly for 110V and monthly for 230V.
- An RCD is a second line of defence
- It detects some, but not all, faults, so a shock can still be fatal. Never bypass one, and treat every trip as a fault to find before the tool goes back into use.
- You need not touch a power line to be hurt by it
- HSE warns that a close approach to live conductors can cause a flashover, that contact can be lethal at voltages as low as 230V, and that current can flow through damp wood or plastic.
What people get wrong
The tool is on an RCD, so a damaged lead does not matter.
An RCD only catches some faults and HSE treats it as a secondary measure. The visual check comes first: an undamaged plug, no exposed internal wires, and no cable patched with tape or an unsuitable connector.
If the RCD trips, reset it and carry on.
A trip means there is a fault. HSE says check the system before using it again, and if it keeps tripping with no fault found, consult the manufacturer of the RCD.
Taping a nicked cable will do until the job is finished.
HSE says damaged cable must be replaced by a competent person and that makeshift repairs must not be made. Take the tool out of service, label it and report it so nobody else picks it up.
110V cannot hurt you.
Centre tapping to earth holds the voltage to earth at about 55V, which makes a fatal shock far less likely. It reduces the risk, it does not remove it, and damaged 110V equipment still comes out of use.
Answering these questions in the test
Four numbers cover most of these questions: 110V for site tools, 55V maximum to earth, 30 mA for an RCD trip, and yellow for the 110V plug. Otherwise the pattern is the usual one. Where one option is a check, a report or an isolation and another is a workaround, take the check. And remember the inspection intervals differ by voltage: on site, user checks are weekly for 110V but every shift for 230V.
Background reading
Drilling the questions tells you what you are getting wrong. It does not always tell you why. For this topic that is covered in Fire Extinguisher Types. Which extinguisher is safe on live equipment, and why electricity is an ignition source rather than a class of fire.
Check which card scheme covers your trade
If you work as an electrician, check this before you book anything. Electrotechnical workers are carded by ECS, not CSCS, and ECS states it cannot accept the CITB test for any of its cards, so a pass here will not get you a card. The route and the exam ECS does want are on ECS card.
Sources
Written from the following. Where a figure could not be verified against one of these, it has been left out rather than approximated. Our sources and methodology explains how we date and re-check them. Spotted something wrong? Report an error and we will fix it.
Topics that come up alongside electrical safety
Ready for the real thing?
When you are scoring 90% or better here, take a CSCS mock test for Operatives under exam conditions, then how to book the CSCS test. Still under 90%? A full CSCS exam test shows which topic to drill next.