Earthing and Bonding Flashcards
6 cards from real ECS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Earthing and Bonding flashcards as text
Which system of earthing has the supply neutral conductor connected directly to earth at the source, with no separate earth conductor run to the consumer?
Answer: TN-C-S (PME) system
In a TN-C-S (PME) system, the neutral and protective functions are combined in a single PEN conductor from the source, with the earth provided at the consumer's installation by connection to this combined conductor.
What danger can arise if main protective bonding is not carried out on incoming metal water pipes?
Answer: The pipe could become live due to a fault elsewhere, causing electrocution to someone touching it and another earthed part simultaneously
Without bonding, an electrical fault could energize an incoming metal pipe, creating a dangerous touch voltage between the pipe and any earthed metalwork or ground.
When testing earth fault loop impedance, the measured value must not exceed the maximum value (Zs max) for the circuit's protective device — why?
Answer: To guarantee the protective device disconnects the supply within the required time under fault conditions
If Zs exceeds Zs max, the fault current will be too low for the protective device to disconnect quickly enough, leaving dangerous touch voltages present for longer than the permitted time.
What is the purpose of a 'combined protective and neutral' (PEN) conductor in a TN-C system?
Answer: To carry both the normal return current and provide the protective earth function in a single conductor
A PEN conductor serves both as the return path for normal load current and as the protective earth conductor, which reduces cable quantity but introduces certain hazards if the PEN conductor breaks.
Under what circumstances might an electrician need to install supplementary bonding even though the installation already has main bonding?
Answer: In locations of increased shock risk, such as bathrooms, where the basic protection requirements alone may not be sufficient
Supplementary bonding is required in special locations like bathrooms where simultaneous contact with multiple conductive parts is likely and body resistance is reduced by moisture.
What action should an electrician take before disconnecting the main bonding conductor to a gas installation for any reason?
Answer: Ensure the gas supply is isolated and notify the gas utility, restoring bonding immediately after work is complete
Removing main bonding from a gas installation removes the protection against touch voltage on the pipework and must be done only with appropriate isolation and immediate restoration to prevent shock risk.