Testing

• What is the title of Section 3 Part A in the Domestic Electrical Installer guidelines?

  Electrical Testing
• What is the purpose of the tests mentioned in the Electrical Testing section?

  To ensure compliance with BS 7671
• What is the prescribed sequence of electrical tests?

  • 'Dead' Tests (supply de-energised):
  • Continuity of circuit protective conductors
  • Continuity of ring final circuit conductors
  • Insulation resistance
  • Polarity
  • 'Live' Tests (supply energised):
  • External earth fault loop impedance (Ze)
  • Circuit earth fault loop impedance (Zs)
  • PFC & PSC
  • Testing of RCDs
• Why must the prescribed test sequence be followed?

  Because each test's satisfactory outcome is necessary for the subsequent test
• What happens if there is a deviation from the prescribed test sequence?

  It negates the testing
• What condition must all test equipment meet before use?

  All test equipment must be undamaged and within calibration
• What precaution should be taken during electrical testing?


  Exercise extreme caution to avoid electric shock
• What should be done once the testing has been completed?

  Record the results on a generic schedule of test results
• What is the purpose of 'dead' tests in electrical installations?


  To ensure continuity of circuit protective conductors
• What does the continuity test ensure between the Consumer's Main Earthing Terminal and the Supply Earthing Arrangements?


  It ensures the consumer's main earthing terminal is at earth potential of zero volts
• What facilitates the connection between the Consumer's Main Earthing Terminal and the earth potential?


  The Main Earthing Conductor
• What is the role of Main Protective Bonding Conductors?


  To prevent extraneous conductive parts from rising above earth potential
• What types of extraneous conductive parts are connected to the Consumer's Main Earthing Terminal?


  Gas, water, oil service pipelines, structural steelwork, air-conditioning ductwork, and lighting conductors
• Why is supplementary bonding necessary in special locations like kitchens and bathrooms?


  To prevent dangerous potentials existing between extraneous conductive parts
• What do Circuit Protective Conductors & RCDs provide in an electrical installation?


  A path for Fault Current to be safely carried away to earth
• What must be ensured about the cables during testing?


  They must be electrically continuous throughout their length with no breaks
• What can cause high resistances in circuit protective conductors?


  A loose or corroded connection
• What is the consequence of excessive voltage drop in cables?


  It can lead to the cable length being too long
• What does the instrument used for testing provide?


  A resistance reading in ohms (Ω)
• What does the R1 + R2 method involve?


  Using the line conductor as a return path and involves two measurements
• What is the first step in the R1 + R2 test method?


  Link L - E at the consumer unit and measure the resistance of the L-E loop
• What should be done with the R1 + R2 readings?


  They should be recorded on the Generic Schedule of Test Results
• What is confirmed while taking the measurement in the R1 + R2 test?


  The polarity of the circuit
• What is the purpose of dividing the L-N reading by 2 in the R1 + R2 method?


  To subtract the result from the L-E loop reading
• What does R1 represent in the context of the R1 + R2 test?


  The resistance of the Circuit Protective Conductor (CPC) for that circuit
• What is the primary purpose of testing protective conductors?


  To ensure that continuity exists
• What can the result of an R1 + R2 calculation also be used to determine?


  The earth fault loop impedance at the accessory
• What are the key components involved in the continuity of circuit protective conductors?


  • Consumer's Main Earthing Terminal
  • Supply Earthing Arrangements
  • Main Earthing Conductor
  • Main Protective Bonding Conductors
  • Supplementary Bonding Conductors
  • Circuit Protective Conductors & RCDs
• What are the steps involved in the R1 + R2 test method?


  1. Link L - E at consumer unit and measure L-E loop resistance.
  2. Record R1 + R2 readings.
  3. Link L - N at consumer unit and measure L-N loop resistance.
  4. Divide L-N reading by 2 and subtract from L-E loop reading.
  5. Repeat for remaining circuits.
• What are the consequences of not ensuring continuity in circuit protective conductors?


  • Risk of dangerous potentials
  • Potential for electric shock
  • Failure of protective devices