Electrical Safety: Shock Effects, Earthing, RCDs and Controls (NEBOSH Notes)

⚡ Electrical Safety: Shock Effects, Earthing, RCDs and Controls

Electricity can kill without warning. This guide explains the main electrical hazards, what happens to the body in a shock, and the control measures you must know for NEBOSH exams.

Electrical safety NEBOSH study notes banner with a high-voltage warning sign

Main electrical hazards

Electric shock

Current passes through the body and can cause injury or death.

Burns

From contact with live parts or arcing (a flash of electrical energy).

Fire

Overloaded circuits, faulty wiring and overheated equipment.

Explosion

Sparks igniting flammable gases, vapours or dust.

Secondary injuries

Falls and other accidents after a person jerks away from a shock.

What affects how severe a shock is?

Size of the current flowing through the body (this is the main danger)
Voltage of the supply
Path through the body: a path across the chest and heart is the most dangerous
Duration: the longer the contact, the worse the harm
Body resistance: wet skin and damp conditions reduce resistance and increase current
Type of supply: AC and DC affect the body differently

Effects of electricity on the body

Diagram showing the current path across the chest and the five effects of electric shock on the body — Effects of electric shock and the factors that decide how severe it is.

Muscle contraction, making it hard to let go
Breathing difficulty or stopping
Heart rhythm disturbance (ventricular fibrillation) or heart stopping
Burns at entry and exit points, and deep internal burns
Secondary injuries from falling

If someone is being shocked: do not touch them. Switch off the power or isolate the supply first, then call for emergency help and give first aid if trained. Touching them first could make you a second casualty.

Control measures: from best to weakest

Isolate / avoid live workSwitch off, lock off and test dead before working

Reduce the dangerReduced low voltage (such as 110 V centre-tapped) for site tools, battery tools

Safety devicesEarthing, double insulation, fuses, circuit breakers and RCDs

Safe working and checksCompetent people, inspections, good cables and plugs, PPE

Electrical control measures ranked from best to weakest, with the double insulation symbol and portable appliance checks — Control hierarchy, double insulation symbol and levels of portable appliance checks.

Key terms made simple

Isolation

Cutting off the supply and locking it off so it cannot be switched on by mistake.

Earthing

Gives fault current an easy path to earth, so the protective device operates and the metal casing does not stay live.

Double insulation

Two layers of insulation, so no earth wire is needed. The equipment shows a double-square symbol.

Fuse or circuit breaker

Protects against overcurrent and overload by breaking the circuit.

RCD

Detects a small leakage of current and cuts the supply very quickly. Often used for extra protection against shock.

Reduced low voltage

A lower voltage supply that reduces the severity of shock, used for tools on construction sites.

Diagram showing how earthing carries fault current to earth and how an RCD cuts the supply when it detects leakage — How earthing and an RCD protect against electric shock.

Remember: an RCD does not replace good maintenance. It is an extra layer of protection, not the only one.

Portable appliance checks

Portable equipment is used often, moved around and easily damaged. Common faults and bad practices include:

Damaged or taped-up cables and exposed wires
Cracked plugs and loose connections
Wrong fuse rating or overloaded socket adaptors
Pulling a plug out by the cable
Using equipment in wet areas without protection

Checks include user checks before use, formal visual inspections, and combined inspection and testing by a competent person. How often you inspect depends on the type of equipment, how it is used, the environment and its past fault history.

Exam practice

Q1. Outline factors that affect the severity of an electric shock.

Size of the current and voltage
Path through the body
Duration of contact
Body resistance and wet conditions
Type of supply (AC or DC)

Q2. Explain the terms “earthing” and “double insulation”.

Earthing: provides a low-resistance path to earth for fault current, so the protective device operates and exposed metal does not stay live.

Double insulation: equipment with two layers of insulation, so a fault is much less likely to make the casing live.

Q3. Outline precautions when using portable electrical equipment.

Check equipment and cable before use
Use RCD protection or reduced low voltage where suitable
Keep cables protected from damage and water
Regular inspection and testing by a competent person
Remove damaged equipment from use and report it

Keep learning

Related topic: manual handling and safe lifting. Browse more free NEBOSH study material on HSEDOT.

HSEDOT is an independent educational blog and is not affiliated with or endorsed by NEBOSH. Electrical work must only be done by competent people. Always follow your syllabus, site rules and local regulations.

NEBOSH IGC-2 Exam Questions & Answers Part-2 (very very useful and simple )

November 04, 2015

Element 5: Electrical safety 1. Identify the possible effects of electricity on the body. (page no: 5-2) § Electric shock – severe electric shock can cause involuntary muscle grip, heart fibrillation, respiratory failure and cardiac arrest. § Burns – burns can also result from an electric shock, at the point of contact and at the point that the current flows out of the body. There may also be internal burns along the current path. § Fire and explosion. § Arcing. § Secondary effects. 2. Outline four factors that may affect the severity of injury from contact with electricity (page no: 5-3) Several factors influence the severity of injury associated with receiving an electric shock: Voltage – as Ohm’s law shows there is a simple relationship between voltage and current, the higher the voltage, the greater the current. Duration – the length of time that a person is exposed to the flow of electricity is critical. For example, a current flow of 60 mA for 30 ...