Equipment Classification

What is a Class I electrical appliance?

• AEquipment with no earth connection
• BEquipment which operates only at extra-low voltage and therefore needs no protective earth
• CEquipment with a single layer of insulation and an earth wire for protection✓
• DEquipment with double insulation

Answer: Class I equipment relies on single insulation plus an earthing conductor for protection. If insulation fails, the earth wire provides a safe path for fault current.

What is a Class II electrical appliance?

• AEquipment that is fitted with reinforced cables and a heavy-duty moulded plug
• BEquipment with an earth wire
• CEquipment used only in industry
• DEquipment with double insulation and no earth connection required✓

Answer: Class II equipment has double insulation providing two levels of protection. No earth wire is needed because even if outer insulation fails, inner insulation provides protection.

What is a Class III electrical appliance?

• AEquipment that is intended to be used only out of doors
• BEquipment with a three-pin plug
• CEquipment powered from a SELV supply of no more than 50V AC or 120V DC✓
• DEquipment with triple insulation

Answer: Class III equipment relies for protection against electric shock on being supplied from a separated extra-low voltage (SELV) source, at no more than 50V AC or 120V DC, and generates no higher voltage inside. The supply arrangement, not just a low working voltage, defines the class: a mains-powered charger or adaptor that feeds such equipment is itself Class I or Class II.

Which class of equipment requires the most stringent testing?

• AClass I✓
• BClass II (double insulated)
• CAll classes require equal testing
• DClass III (extra-low voltage)

Answer: Class I equipment typically requires more comprehensive testing because it relies on a single insulation layer plus earthing, making it more vulnerable if insulation fails.

How can you identify a Class II appliance?

• ABy the presence of an earth pin on the moulded plug top
• BBy the overall weight of the appliance when it is lifted
• CBy the colour of the outer sheath on the flexible cable
• DBy a double square symbol on the rating label✓

Answer: Class II equipment is marked with a double square symbol (□□) on the rating label or instructions, indicating double insulation protection.

What starting interval does HSE suggest for a combined inspection and test of a Class I kettle in an office?

• A6 months
• B3 years
• C12-24 months✓
• DWeekly

Answer: HSE's leaflet INDG236 suggests a combined inspection and test every 1-2 years for earthed (Class I) equipment that is moved about, such as kettles, in a low-risk environment such as an office. It is a starting point, adjusted by risk assessment and the results found.

Which type of equipment would include a computer monitor?

• ABoth Class I and Class II depending on construction✓
• BClass I, because a monitor's metal chassis needs an earth
• CClass II, because monitors have a plastic outer casing
• DClass III, because monitors run from an extra-low voltage supply

Answer: Computer monitors can be either Class I (with earth pin) or Class II (double insulated). Classification depends on the manufacturer's design and insulation method.

What is 'Extra-Low Voltage' (ELV)?

• ANot more than 50V AC or 120V DC✓
• BBetween 50V and 230V
• CMore than 400V
• DAny voltage above 25V

Answer: Extra-low voltage (ELV) is not more than 50V AC or 120V ripple-free DC. It lowers the risk of electric shock but does not remove it in every condition, which is why SELV and PELV systems add separation or earthing rules.

Which equipment class would include a double-insulated power drill?

• AClass I
• BIndustrial class
• CClass II✓
• DClass III

Answer: Double-insulated power tools are Class II equipment, featuring plastic casings and double insulation throughout their design.

What is the main advantage of Class II equipment?

• AIt provides double protection through insulation, not requiring an earth connection✓
• BIt can never be damaged during normal everyday use on site
• CIt costs less to manufacture
• DIt works on lower voltages

Answer: The main advantage of Class II is that it provides protection through its construction (double insulation) rather than relying on an earth connection, making it safer in some situations.

Which class of equipment MUST have an earth connection?

• AClass II
• BAll classes
• CClass I✓
• DClass III

Answer: Class I equipment must have an earth connection as part of its safety system. Class II doesn't require it due to double insulation.

What type of appliance is a metal-cased electric kettle typically?

• AClass I (with earth pin)✓
• BClass III
• CClass II (double insulated)
• DClass 0 (unearthed)

Answer: Metal-cased appliances are typically Class I because metal can conduct electricity. They require an earth wire for safe operation if insulation fails.

What does SELV stand for?

• ASafe Electrical Low Voltage
• BSystem for Extra Low Voltage
• CStandard Emergency Low Voltage
• DSeparated Extra Low Voltage✓

Answer: In BS 7671, SELV stands for separated extra-low voltage: an extra-low voltage system kept electrically separate from earth and from other systems, so a single fault cannot raise it above extra-low voltage. The older name 'safety extra-low voltage' is still seen in some texts.

Which piece of IT equipment is most likely to be Class II?

• AKeyboard with plastic casing and double insulation✓
• BAll IT equipment is Class I because it is fitted with a moulded plug
• CA desktop computer tower built into an earthed metal casing
• DA computer monitor that is housed inside an earthed metal casing

Answer: IT equipment with plastic casings and double insulation design (like many keyboards and mice) is typically Class II.

What is the primary reason Class III equipment doesn't require earthing?

• AEarthing them would damage the internal circuits
• BThey are fitted with a fuse in the plug instead
• CThey draw too little current to need an earth
• DIt is fed from a SELV supply limited to extra-low voltage✓

Answer: Class III equipment is protected against electric shock by its supply: it is fed from a separated extra-low voltage (SELV) source, at no more than 50V AC or 120V DC, and generates no higher voltage inside, so it needs no protective earth. That protection depends on the supply staying SELV; a low working voltage from an unsuitable source does not make equipment Class III.

A car battery charger plugs into a 230V socket and has a 12V DC output. What class of equipment is the charger itself?

• AClass I or Class II, depending on how it is built✓
• BClass III, because its output is extra-low voltage
• CClass 0, because it is not fitted with an earth pin
• DExempt from classing, as it is used only occasionally

Answer: Class III equipment is supplied from a SELV source, at no more than 50V AC or 120V DC, and generates no higher voltage inside. A battery charger takes its supply from the 230V mains, so its protection against shock depends on earthing (Class I) or double or reinforced insulation (Class II); a low output voltage does not change that. HSE's HSG107 includes battery charging equipment among the items that need formal visual inspection and combined inspection and testing.

What does double insulation consist of in Class II equipment?

• ATwo separate power cables
• BTwo layers of protective insulation between live parts and accessible surfaces✓
• CTwo separate plugs fitted to opposite ends of the same lead
• DTwo separate earth connections

Answer: Double insulation provides two independent layers of insulation between live parts and any surface a person could touch, eliminating the need for earthing.

Which class of equipment would a handheld electric hair dryer typically be?

• AClass III
• BClass I
• CCan be either Class I or II✓
• DClass II

Answer: Hair dryers can be either Class I (with earth pin) or Class II (double insulated plastic body), depending on the manufacturer's design.

What is the relationship between equipment class and testing requirements?

• AClass III equipment is tested more often than Class I, as it runs at low voltage
• BClass II needs an earth continuity test, like Class I
• CTesting is independent of equipment class
• DClass I may require more comprehensive testing than Class II due to its reliance on earthing✓

Answer: Class I equipment may require more comprehensive testing because it depends on the earth connection for safety; Class II relies on insulation alone.

What is a portable appliance?

• AEquipment that is less than 50kg
• BEquipment that is hard-wired into the fixed installation but can be unbolted
• CEquipment that is not permanently fixed to the building✓
• DAny appliance which is able to move around by itself under its own power

Answer: A portable appliance is equipment that is not permanently fixed to the building's electrical installation, making it suitable for PAT testing.