Earthing & Bonding Flashcards
6 cards from real PART P 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 & Bonding flashcards as text
What is a bonding clamp and what standards must it comply with?
Answer: A mechanical connector used to make the bonding connection to a metallic pipe or service, complying with BS 951
A bonding clamp is a purpose-made connector complying with BS 951 that provides a reliable, durable mechanical and electrical connection between the bonding conductor and metallic service pipes.
Why must bonding clamps be positioned on the consumer's side of any insulating joints in a metallic service pipe?
Answer: To ensure that only the pipework within the building (which could be energised) is bonded — if bonded on the supply side, the insulating joint would disconnect the bonding from the relevant pipework
Insulating joints are sometimes fitted in gas and water services to electrically separate the external supply from the internal installation; bonding must be on the consumer's side to earth the metalwork that is actually inside the building.
In a TN-C-S (PME) system, what is the danger of an open-circuit (broken) PEN conductor in the supply network?
Answer: All bonded metalwork in the installation would rise to near line voltage (230 V) as the neutral return path is the same conductor as the earth
In a PME system, neutral and earth are the same conductor in the supply network; if it breaks, the load current returning via the neutral would raise the 'earth' to near line voltage — all bonded metalwork would become live at dangerous voltage.
What label must be fixed to the earthing conductor where it connects to the earth electrode?
Answer: 'Safety electrical connection — do not remove' (as specified in BS 7671 Regulation 514.13)
BS 7671 Regulation 514.13 requires a durable label reading 'Safety electrical connection — do not remove' to be fixed at the connection between the earthing conductor and the earth electrode, warning against inadvertent disconnection.
What is the minimum burial depth for a buried earthing conductor to provide protection from mechanical damage?
Answer: 600 mm for conductors in the ground (though physical protection is preferred for cables at risk)
Buried earthing conductors should be at a depth that protects them from mechanical damage; 600 mm is a commonly referenced minimum for buried conductors in ground, though protection depends on the risk assessment for the specific site.
What is the connection between PME earthing and electric vehicle charge points?
Answer: PME earth may not be suitable for EV charge points on a TN-C-S supply without additional protection (e.g., a PEN conductor fault detection device or a separate earth electrode) to prevent dangerous touch voltages from a broken PEN conductor
BS 7671 and EV charge point guidance require that PME-earthed charge points installed outdoors include PEN conductor fault detection (or a separate earth electrode) to protect against the risk of dangerous touch voltages if the PME PEN conductor breaks.