At a rural bungalow the supply gives no earthing terminal at all, and the installation is earthed by its own rod. Which system is this?

With no earth from the supply and the installation earthed through its own electrode, the system is TT, and earth fault protection relies on RCDs. TN-S would have a separate protective conductor from the source, and TN-C-S, normally provided as PME in the UK, takes the earthing terminal from the combined PEN conductor.

What voltage threshold does Regulation 722.411.4.1 set for methods (b) and (c)?

Methods (b) and (c) work to 70 V: the MET held to 70 V RMS or less for (b), and a device acting above 70 V RMS CPC-to-Earth for (c). Method (d) uses a 207–253 V line-to-neutral band instead. 50 V is the TT condition RA × IΔn ≤ 50 V, a different test for a different job.

Apart from raising the potential of the MET, what else does an open PEN on the network do inside a PME installation?

With the PEN open, load current returns through the MET, the earthing conductor, the protective conductors and the main bonding, and out through metalwork with a path to Earth. That is why 544.1.1 sizes main bonding from the supply PEN where PME conditions apply. RCDs see balanced line and neutral currents and MCBs see normal load, so the installation keeps working while the hazard is present.

Trips every 30 mA RCD in the consumer unit

Sends load current through the main bonding

Makes the MCBs trip on overload straight away

Reverses the polarity at every socket-outlet

Free mock exam

Earthing and PME — EV Charging Installation Practice

Free topic-focused mock exam: all 30 questions on Earthing and PME, drawn from the wider EV Charging Installation bank. 35-minute timer, 70% to pass, worked explanation on every question. Use this when you've taken the full mock once and want to drill the topics you got wrong.

Questions: 30
Time limit: 35 min
Pass mark: 70% · 21/30
Question bank: 30

Free, no sign-up. Retake as many times as you like — the questions are reshuffled, with the answer order changed.

Sample questions

01At a rural bungalow the supply gives no earthing terminal at all, and the installation is earthed by its own rod. Which system is this?
- APME
- BTN-C-S
- CTN-S
- DTT
Why: With no earth from the supply and the installation earthed through its own electrode, the system is TT, and earth fault protection relies on RCDs. TN-S would have a separate protective conductor from the source, and TN-C-S, normally provided as PME in the UK, takes the earthing terminal from the combined PEN conductor.
02What voltage threshold does Regulation 722.411.4.1 set for methods (b) and (c)?
- A50 V
- B70 V
- C120 V
- D25 V
Why: Methods (b) and (c) work to 70 V: the MET held to 70 V RMS or less for (b), and a device acting above 70 V RMS CPC-to-Earth for (c). Method (d) uses a 207–253 V line-to-neutral band instead. 50 V is the TT condition RA × IΔn ≤ 50 V, a different test for a different job.
03Apart from raising the potential of the MET, what else does an open PEN on the network do inside a PME installation?
- AMakes the MCBs trip on overload straight away
- BTrips every 30 mA RCD in the consumer unit
- CSends load current through the main bonding
- DReverses the polarity at every socket-outlet
Why: With the PEN open, load current returns through the MET, the earthing conductor, the protective conductors and the main bonding, and out through metalwork with a path to Earth. That is why 544.1.1 sizes main bonding from the supply PEN where PME conditions apply. RCDs see balanced line and neutral currents and MCBs see normal load, so the installation keeps working while the hazard is present.

Common questions

Is the Earthing and PME mock exam free?

Yes — 100% free, no sign-up needed. Questions are pulled at random from a substantial bank, with a worked explanation on every question after you submit.

Can I retake the mock exam?

Yes. Every attempt picks a different random selection and reshuffles the options, so each retake gives you genuinely new questions. No limit on retakes.

Does this count towards the real qualification?

No — this is independent practice material. To gain the actual qualification you need to sit the official assessment through an approved provider.