Part P Testing and Inspection 2 — Questions and Answers
Question 1: During an RCD test, what trip times are acceptable for a 30mA Type AC RCD when tested at rated residual current (IΔn)?
- Must trip within 200ms
- Must trip within 300ms (Correct answer)
- Must trip within 40ms
- Must trip within 1000ms
Correct answer: Must trip within 300ms
When tested at rated residual current (IΔn = 30mA), a general-purpose (non-time-delayed) RCD must trip within 300ms. When tested at 5 × IΔn (150mA), it must trip within 40ms. The 300ms limit at rated current ensures reliable operation, while the faster 40ms at 5× ensures rapid disconnection for more serious fault currents.
Question 2: What does a Periodic Inspection Report (PIR/EICR) code C2 signify?
- Danger present — immediate remedial action required
- Potentially dangerous — urgent remedial action required (Correct answer)
- Improvement recommended — not a safety concern
- The installation passes with no issues
Correct answer: Potentially dangerous — urgent remedial action required
Code C2 (Potentially Dangerous) indicates a fault that, while not presenting immediate danger, could become dangerous if not addressed. Urgent remedial action is required. Code C1 indicates immediate danger requiring urgent action. Code C3 indicates an improvement is recommended. Code FI means further investigation is needed.
Question 3: When performing a continuity test on a protective conductor, what type of instrument is used?
- A clamp meter
- A low-resistance ohmmeter (typically using a test current of at least 200mA DC) (Correct answer)
- A voltage tester
- An insulation resistance tester
Correct answer: A low-resistance ohmmeter (typically using a test current of at least 200mA DC)
Continuity testing uses a low-resistance ohmmeter that delivers a test current of at least 200mA DC. This ensures that the measurement can detect poor connections and resistive joints that would not be revealed by a high-impedance instrument. The instrument must be calibrated and the test lead resistance nulled (zeroed) before taking measurements.
Question 4: At what maximum interval does BS 7671 recommend periodic inspection and testing of a domestic electrical installation?
- Every year
- Every 5 years or at change of occupancy
- Every 10 years or at change of occupancy (Correct answer)
- Only when a fault is suspected
Correct answer: Every 10 years or at change of occupancy
IET Guidance Note 3 recommends periodic inspection and testing of domestic installations every 10 years or at change of occupancy (tenancy or ownership). For rented properties, the interval is 5 years as required by the Electrical Safety Standards in the Private Rented Sector (England) Regulations 2020. Regular inspection identifies deterioration before it becomes dangerous.
Question 5: During initial verification, the polarity test confirms which critical safety feature?
- That the voltage is correct at 230V
- That single-pole switching devices are connected in the line conductor only, and that the line and neutral are correctly identified throughout (Correct answer)
- That the earth electrode resistance is adequate
- That the main bonding is correctly sized
Correct answer: That single-pole switching devices are connected in the line conductor only, and that the line and neutral are correctly identified throughout
Polarity verification ensures that all single-pole switches and protective devices are connected in the line (live) conductor, that socket outlets are correctly wired (line to line terminal, neutral to neutral terminal, earth to earth terminal), and that the line and neutral conductors are correctly identified throughout. Reversed polarity is a serious safety hazard.
Question 6: What is the purpose of the R1 + R2 measurement taken during continuity testing?
- To calculate the voltage drop
- To verify that the earth fault loop impedance at the furthest point will be within limits for the protective device to operate within the required disconnection time (Correct answer)
- To check the insulation resistance
- To measure the load current
Correct answer: To verify that the earth fault loop impedance at the furthest point will be within limits for the protective device to operate within the required disconnection time
The R1 + R2 measurement (resistance of the line conductor plus the resistance of the CPC from the origin to the furthest point of the circuit) is added to the external earth fault loop impedance (Ze) to calculate the total earth fault loop impedance (Zs = Ze + R1 + R2). This confirms that the protective device will disconnect within the required time during a fault.
Part P Testing and Inspection 2
During an RCD test, what trip times are acceptable for a 30mA Type AC RCD when tested at rated residual current (IΔn)?