Electrical Testing

What is earth continuity testing?

• AChecking if the equipment is grounded to the building
• BTesting the insulation of the cable along with its outer sheath
• CTesting the voltage between live and earth
• DMeasuring the resistance of the earth circuit to ensure a safe path for fault current✓

Answer: Earth continuity testing measures the resistance of the earth path to ensure it's low enough to safely carry fault current. This is critical for Class I equipment.

Under the IET Code of Practice (5th edition), what earth continuity limit applies to a Class I appliance itself, before its supply cord's resistance is added?

• A5.0 Ohms
• B2.0 Ohms
• C1.0 Ohm
• D0.1 Ohms✓

Answer: The limit is (0.1 + R) ohms, where R is the resistance of the supply cord's protective conductor, so the appliance itself is allowed 0.1 ohm, and an item with no supply cable 0.1 ohm in total. The 5th edition also lets the duty holder accept up to 0.5 ohm on older equipment where they are satisfied the reading is not caused by deterioration.

What is insulation resistance testing?

• ATesting how long the equipment lasts
• BMeasuring the overall length of the appliance's mains cable
• CTesting the outer cable covering
• DMeasuring the resistance between live parts and earth to detect insulation breakdown✓

Answer: Insulation resistance testing applies a test voltage and measures the resistance between live conductors and earth, detecting insulation deterioration.

What is the minimum insulation resistance for Class I equipment at 500V DC?

• A2.0 MΩ
• B5.0 MΩ
• C0.1 MΩ (megaohms)
• D1.0 MΩ✓

Answer: Under the IET Code of Practice (5th edition), Class I equipment must show an insulation resistance of at least 1.0 MΩ, normally tested at 500 V d.c., or at 250 V d.c. where surge protection or IT equipment makes 500 V unsuitable.

What is touch current testing?

• ATouching the equipment during testing
• BTesting if the equipment is hot to touch
• CMeasuring leakage current that could flow through a person touching the equipment✓
• DTesting hand-held equipment only, and nothing else at all

Answer: Touch current (leakage current) testing measures the current that would flow through a person if they touched the equipment when it's operating normally.

Under the IET Code of Practice (5th edition), what is the touch current limit for Class II equipment?

• A0.25 mA
• B1 mA
• C5 mA✓
• D10 mA

Answer: The 5th edition applies the same 5 mA limit to touch current on Class II equipment as to protective conductor current on Class I. The 4th edition's 0.25 mA figure for Class II touch current was replaced by this single limit.

What test equipment is used for earth continuity testing?

• AA thermal imaging camera pointed at the plug and the cable
• BA pressure gauge connected across the earth conductor of the flex
• CA digital multimeter on its own, set to the resistance range
• DA PAT tester with an earth continuity test function✓

Answer: A dedicated PAT tester with earth continuity test capability applies a test current (typically 200mA) and measures the resistance.

What test voltage is typically used for insulation resistance testing on Class I equipment?

• A500V DC✓
• B50V DC
• C1000V DC
• D250V DC

Answer: 500V DC is the standard insulation-resistance test voltage for mains-voltage portable appliances; 250V DC is used for sensitive electronic/IT equipment where a false low reading or damage risk is a concern.

What does a PAT tester do?

• APerforms automated electrical testing and usually provides pass/fail results✓
• BMeasures the energy an appliance uses so that running costs can be worked out
• CRepairs the faults it finds and resets the appliance
• DMeasures the supply voltage at the wall socket

Answer: A PAT tester (also called a portable appliance tester) performs automated electrical tests including earth continuity, insulation resistance, and touch current.

How is the earth continuity test performed on a Class I appliance?

• ABy applying a test current between the live pin and the earth pin
• BBy measuring the voltage between the live and the neutral pins at the plug top while under load
• CBy visual inspection only, no test current required
• DBy applying a test current between the earth pin and an accessible conductive/metal part of the casing, and measuring the resistance✓

Answer: Earth continuity verifies the protective earth path is intact by applying a test current between the earth pin of the plug and an accessible/exposed conductive part of the casing, and measuring the resistance — it does not involve the live conductor.

What is 'insulation breakdown'?

• AThe normal ageing of equipment that happens to every appliance over time
• BDeterioration of insulation allowing current to leak to earth✓
• CWhen the equipment stops working altogether and will no longer switch on
• DWhen the cables are removed from the plug

Answer: Insulation breakdown occurs when insulation material deteriorates, allowing electrical current to flow where it shouldn't, creating shock and fire hazards.

How often should insulation resistance testing be performed?

• AOnce, at the point at which the equipment is first taken into service
• BAt seven-yearly intervals, set by the IET for each equipment class
• CAfter the equipment has failed or been reported as faulty
• DSet by risk assessment; up to 5 years for earthed office IT✓

Answer: Insulation resistance is measured as part of the combined inspection and test, whose frequency HSE's HSG107 leaves to the dutyholder's risk assessment. Suggested starting intervals range from monthly for 230V construction equipment, through 1-2 years for earthed equipment such as kettles, to up to 5 years for rarely moved earthed office IT; double-insulated office IT needs no routine test. The intervals are then adjusted in light of the results.

What is the difference between leakage current and touch current?

• ALeakage current is measured in amps, touch current in volts
• BOne of them is always measured as AC current and the other as DC
• CThey are two names for the same thing
• DLeakage is current to earth through insulation; touch current is current through a person✓

Answer: Leakage current is the current flowing to earth through the insulation. Touch current specifically measures the current that would flow through a person contacting the equipment.

Why is earth continuity testing important for Class I equipment?

• AIt verifies the earth connection can safely carry fault current if insulation fails✓
• BIt is of no real importance for any equipment of this class
• CIt measures how much power the equipment uses
• DIt tests the cable insulation

Answer: If Class I equipment develops an insulation fault, the earth connection must be able to carry fault current safely to prevent electric shock.

What happens if earth continuity resistance is too high?

• AThe equipment becomes more efficient because less of the current is wasted as heat
• BSafety is unaffected
• CThe earth path cannot safely carry fault current, creating a shock hazard✓
• DThe equipment works better

Answer: High earth continuity resistance means the earth path cannot safely carry fault current, creating a serious shock hazard.

What is the test current typically used in earth continuity testing?

• A1 mA
• B10 mA
• C100 mA
• D200 mA✓

Answer: A test current of 200 mA (0.2 A) is typically used for earth continuity testing. This is strong enough to measure accurately but safe for testing purposes.

Why shouldn't Class II equipment be tested for earth continuity?

• AIt's not necessary - Class II doesn't rely on earthing for safety✓
• BAll classes need this test
• CTesting would damage it
• DThe double insulation would be punctured by the 200 mA earth test current

Answer: Class II equipment doesn't have or need an earth connection because it relies on double insulation for protection, not earthing.

What does it mean if insulation resistance reading is 'very high' or 'infinite'?

• AThe test has failed and the item must be withdrawn
• BThe insulation is in excellent condition✓
• CThe PAT tester itself is faulty and needs recalibrating
• DThe equipment is broken and no longer draws current

Answer: Very high or infinite insulation resistance (above 1 MΩ for Class I) indicates good insulation with no breakdown.

What is 'functional testing' in PAT?

• AA test of the fixed wiring circuit that feeds the socket
• BA measurement of the appliance's protective conductor current
• CTesting the appliance under a full electrical load for a period of thirty minutes
• DA brief operational test to confirm the equipment functions as intended✓

Answer: Functional testing is a brief check to confirm the equipment operates properly (e.g., a kettle heats water). This can identify some faults.

What is the minimum insulation resistance acceptable for Class II equipment?

• A0.5 MΩ
• B7.0 MΩ
• C1.0 MΩ
• D2.0 MΩ✓

Answer: Class II equipment relies on double or reinforced insulation, so the IET Code of Practice (5th edition) sets a higher minimum insulation resistance of 2.0 MΩ, twice the 1.0 MΩ required for Class I.

Why are earth continuity and insulation resistance tests done with the appliance disconnected from the mains?

• AThe tester applies its own test voltage or current, so mains power is not needed✓
• BThe appliance must be running at full working load for the readings to count
• CIt is quicker for the tester, and the results are the same either way
• DIt saves electricity during a long day of testing on site

Answer: A PAT tester applies its own test current for earth continuity and its own test voltage for insulation resistance, so the appliance is tested disconnected from the mains. Connecting mains during these tests would be unsafe and would distort the readings.

What should you do if an insulation resistance test shows a failing result?

• AAttempt to repair the insulation fault yourself before retesting
• BIgnore the reading, since it is only a number shown on the display
• CImmediately fail the equipment and remove it from service✓
• DTest the equipment again at a later date

Answer: Failed insulation resistance indicates serious insulation breakdown. The equipment must be immediately removed from service.

What measurement unit is used for insulation resistance?

• AWatts
• BAmperes
• CVolts
• DOhms (or MΩ - megaohms)✓

Answer: Insulation resistance is measured in Ohms. For large resistances, it's expressed in megaohms (MΩ), where 1 MΩ = 1,000,000 Ohms.

What is 'RCD testing' in the context of PAT?

• AIt forms no part of standard PAT work in any circumstances
• BTesting the residual current device function✓
• CRandom current testing carried out on a sample of items
• DRelative condition diagnosis of the appliance casing

Answer: RCD (Residual Current Device) testing checks that the RCD trips within the correct time at the correct fault current. This is important for extension leads with RCDs.

How should earth continuity be measured on a Class I plug?

• ABetween the live pin and the neutral pin on the moulded plug top
• BBetween the earth pin and any accessible conductive part✓
• CBy visual inspection of the plug alone
• DWith a multimeter on its resistance range, using no test current at all

Answer: Earth continuity is measured from the earth pin to all accessible conductive parts to ensure a complete path.

What is the purpose of 'cable sheath continuity' testing?

• ATo ensure the outer protective sheath is conducting and can provide earth continuity✓
• BIt plays no part in PAT
• CTo measure cable flexibility
• DTo test the overall length of the appliance's own mains cable

Answer: Cable sheath continuity testing (if the sheath is metallic and used for earthing) ensures it can safely carry fault current.

What routine maintenance does HSE's HSG107 suggest for extra-low voltage equipment, such as a low-voltage desk light?

• AHSG107 suggests no routine user checks, inspections or tests✓
• BThe same formal visual inspections and tests as Class II items
• CThe same combined inspection and test as earthed Class I items
• DMonthly combined tests, as for 230V construction site tools

Answer: HSE's HSG107 Table 1 lists extra-low voltage equipment (below 50V AC), telephone equipment and low-voltage desk lights, and battery-operated equipment below 40V, as needing no user checks, formal visual inspections or combined inspection and test; the guidance is aimed at equipment supplied at a voltage that can give a fatal shock. Any mains-powered charger or transformer feeding such equipment is still maintained as mains equipment, and HSG107 lists battery charging equipment among the items needing inspection and testing.

What does 'combined inspection and test' mean?

• AVisual inspection followed by electrical testing✓
• BUser checks plus a formal visual inspection, without instrument tests
• CAn inspection of the appliance and of the fixed wiring together
• DElectrical testing on its own, with no visual inspection first

Answer: Combined inspection and test is the complete PAT process: first visual inspection, then electrical testing if visual is passed.

What is the purpose of applying a high voltage (500V DC) in insulation resistance testing?

• ATo dry out the insulation by burning off the moisture on its surface
• BTo damage weak insulation deliberately so that it can be identified afterwards
• CTo simulate mains voltage stress and detect insulation breakdown✓
• DTo make the test complete more quickly

Answer: High test voltage (500V DC for 230V mains) simulates stress on the insulation, helping to detect borderline insulation breakdown.

An item passes, but one of its readings is close to the limit. What is the best action?

• ARecord the pass and report the reading so its cause can be checked✓
• BIgnore it, since any reading inside the limit means nothing at all
• CPass it with no further note, as only a fail needs recording
• DFail it straight away and remove it from service as unsafe

Answer: A reading inside the limit is a pass, but one close to the limit may point to a developing fault such as a loose terminal. Recording it lets the result be compared at the next test, and reporting it lets the duty holder decide whether the item needs attention or a shorter interval: HSE's HSG107 notes that records can reveal adverse trends, and the interval is the duty holder's decision, not the tester's.