7.4 Electricity Hazards

7.4 Electricity Hazards

Quick Answer: Electricity causes shock, burns, fire, arcing, and secondary falls. Construction often uses 110 V centre-tapped earth (CTE) reduced voltage. Use RCDs, maintain portable appliance inspection/testing, and enforce isolation / lock-out/tag-out. Live work only when justified, under permit and competent control. Treat underground/overhead services, damaged cables, and wet environments as high risk.

Electricity is a clean, silent, and unforgiving energy source. Managing Safely expects managers to respect it with systems of work — not leave electrical safety solely to “the electrician” while supervisors ignore damaged leads trailing through puddles.

How electricity harms people and property

Current, not voltage alone, drives injury — but higher voltage makes dangerous current more likely. Moisture, damaged insulation, and lack of RCD protection dramatically increase risk even on common mains voltages.

Legal and management framing (overview)

The Electricity at Work Regulations 1989 require electrical systems to be constructed and maintained so far as reasonably practicable to prevent danger, and that work is carried out in a way that prevents danger. In practice for managers:

• Only competent people design, install, maintain, and test electrical systems appropriate to the task complexity
• Equipment must be suitable for the environment (IP rating for dust/water, industrial duty cables)
• Defects must be reported and taken out of service
• Live working is tightly restricted (see below)

You do not need to be an electrician to stop unsafe work, isolate simple user equipment via correct procedures, or refuse to ignore a crushed extension lead.

Reduced voltage: 110 V centre-tapped earth (CTE)

On UK construction sites and many industrial temporary supplies, portable tools and site lighting often run at 110 V from transformers with a centre-tapped earth (CTE) secondary.

Why 110 V CTE is taught

• The winding is centre-tapped to earth so that the voltage to earth from either line is about 55 V, not the full 110 V
• That reduces the severity of a shock to earth compared with 230 V mains tools on site
• It is a risk reduction measure for harsh environments with damaged cables, damp, and rough use — not a claim that 110 V is harmless

Exam point: associate construction portable tools with 110 V CTE reduced voltage, and know it limits voltage to earth via the centre tap.

RCDs — residual current protection

A Residual Current Device (RCD) monitors current balance between live and neutral. If current “leaks” to earth (for example through a person), the RCD trips and disconnects supply quickly when the imbalance exceeds its rating (commonly 30 mA for personal protection in many user situations).

Manager points:

• RCDs reduce risk of fatal shock; they do not replace insulation, good plugs, or isolation discipline
• Use RCDs for portable equipment outdoors, in construction, and other higher-risk situations as risk assessment and regulations/guidance require
• Test RCDs with the trip button on a sensible schedule; arrange formal testing as part of maintenance
• A tripped RCD is information — find the fault; do not keep resetting into a dangerous circuit
• RCDs do not protect against all faults (for example overload between live and neutral without earth leakage may need fuses/MCBs)

Portable appliance inspection and testing (overview)

“PAT testing” is familiar language; the real duty is to maintain equipment so it remains safe. A proportionate regime usually combines:

Risk-based frequencies (manager concept)

There is no single universal “every 12 months for everything” law for all kit. Frequency depends on:

• Equipment type and class
• How often it is used
• Environment (construction and workshops vs quiet offices)
• Users (public vs trained staff)
• Manufacturer instructions and previous fault history

Construction tools need far more frequent attention than a rarely moved office PC. Managers set regimes with competent advice and enforce quarantine of defective kit.

Class I vs Class II (awareness)

• Class I — relies on earth connection for safety of exposed metal; earth continuity critical
• Class II — double/reinforced insulation (often square-in-square mark); still needs cable and enclosure integrity

Isolation and lock-out / tag-out concepts

Unexpected start-up and stored energy kill people during maintenance. Safe isolation means ensuring equipment is disconnected from energy sources and cannot be re-energised accidentally while work continues.

Manager-level principles:

1. Plan the isolation — identify all energy sources (electrical, pneumatic, hydraulic, gravity, batteries).
2. Disconnect using the correct device — not improvised pulling of fuses by untrained staff on complex systems.
3. Secure isolation with locks and retain keys under a controlled system (lock-out).
4. Tag the isolation point with who/why/when (tag-out) so others do not remove it.
5. Prove dead with appropriate test equipment where electrical — “test before touch,” prove the tester, prove the circuit, prove the tester again (competent person practice).
6. Release stored energy and secure mechanical movement.
7. Only remove locks when the work is complete and people are clear — group lock-out where multiple workers are involved.

Supervisors stop culture where someone “just needs power for a second” and removes another person’s lock.

Live work — only when justified

Working on or near live conductors is high risk. Teaching aligned with Electricity at Work expectations:

Live work should only proceed when:

• It is unreasonable to make the system dead (for example certain testing, or continuity of critical life-safety systems where alternatives fail), and
• It is reasonable to work live, and
• Suitable precautions are taken (competence, insulated tools, barriers, accompanying person where needed, PPE, permits)

Many tasks people call “live work” should simply wait for isolation. Permits to work for electrical live working or complex high-voltage tasks formalise authorisation, limits, and precautions. Managers must not pressure electricians to work live to hit production targets without justification.

Underground and overhead services

Underground

Cable strikes during excavation cause burns, flash injuries, explosions (gas), and service outages.

Controls:

• Obtain service drawings and use cable avoidance tools + safe digging practices (HSE HSG47-style approach)
• Permit systems for ground disturbance
• Hand digging near suspected services
• Assume drawings may be incomplete or wrong

Overhead

Contact with overhead power lines by ladders, scaffolds, MEWPs, tipper vehicles, cranes, and irrigation pipes is repeatedly fatal.

Controls:

• Goalposts, barriers, exclusion zones, and route planning
• Observe statutory clearances; consult the distribution network operator when work is near lines
• Lower equipment; use alternative routes; never assume lines are insulated “phone wires”

Damaged cables and wet environments

Worked scenarios

Project application

Electrical hazards on the project should show:

• Specific hazardous events (shock from damaged lead; cable strike; fire from overloaded socket)
• Controls high in the hierarchy (fixed wiring improvements, reduced voltage, cordless tools, eliminate unnecessary live work)
• RCDs, inspection regimes, isolation procedures, competence
• Interaction with height, water, and excavation hazards where relevant

Common exam traps

• Claiming 110 V is completely safe
• Thinking RCDs replace all other electrical controls
• Treating PAT as a fixed annual ritual with no user checks
• Allowing live work for convenience
• Ignoring secondary falls after shock
• Assuming underground maps are always accurate without on-site detection

Manager checklist

1. Recognise electricity’s harm modes: shock, burns, fire, arc, secondary injury.
2. Prefer 110 V CTE for construction portable equipment; use RCDs where residual current protection is needed.
3. Enforce pre-use checks and risk-based inspection/testing; quarantine defects.
4. Make safe isolation and lock-out/tag-out non-negotiable for maintenance.
5. Authorise live work only when justified, with competence and formal controls.
6. Plan for underground and overhead services before dig or high reach.
7. Treat water + electricity + damaged cables as stop-work triggers.

Electrical safety is mostly disciplined boredom: the right voltage system, a tested RCD, a locked isolator, and a replaced cable prevent funerals. Managing Safely asks you to lead that discipline in your area of control.