Mode 3 charging
Charging an electric vehicle on through dedicated charging equipment, such as a wall-mounted charge point. Control signals between the equipment and the car confirm the connection and set how much the car may draw. BS 7671's Section 722 has its own rules for it, including fault currents: with no DC protection in the charge point, the options are a Type B , or a Type A or Type F RCD with an RDC-DD.
Using Mode 3 charging in context
Reviewed
A distinction worth remembering
An RCD's type tells you which kinds of residual current it will reliably respond to. It doesn't tell you how much leakage trips it, which is the mA rating. And it's nothing to do with MCB curves. A Type B RCD and a Type B MCB share a letter and nothing else, because MCB Types B, C and D describe how a breaker responds to overcurrent.
Questions to take further
- How can I revise Mode 3 charging beyond the definition?
- Explain what Mode 3 charging describes, compare it with a related term and use it in a topic question. State any assumptions and what evidence you would need before applying the idea to real work.
Sources
- Professional Electrician: understanding RCDs and their application (Scolmore) — A maker's article, 23 June 2022, written for Amendment 2. Regulation 531.3.3 on Types AC, A and B, blinding, 6 mA smooth DC on Type A, S types and the 3:1 selectivity ratio.
- Professional Electrician: RCD types for EV charging installations (Hager) — A maker's article, 18 December 2024, written for Amendment 3. Type B or Type A or F with an RDC-DD, the 6 mA threshold and why it was chosen.
- Voltimum: Type A or F RCDs? (Doepke) — A maker's article, 20 December 2018, written for the 18th Edition before its amendments. Mixed-frequency current, the 10 mA smooth DC limit on Type F, and three-phase inverters needing Type B.
- IET: initial verification technical webinar questions — Webinar of 5 April 2022. Whether to code a Type AC RCD on a condition report where electronic equipment is installed takes engineering judgement.
- IET: RCD selection, types and testing — Residual-current waveforms, device selection and the distinction from overcurrent protection.
Where Mode 3 charging fits in the learning path
The Low-Carbon Electrics section covers these units:
- EV Charging
- Solar PV and Batteries in Depth
- Heat Pumps, Smart Loads and the Supply
See this section in the full curriculum
This section is on the Plus path. Lesson availability depends on content review and your learning path.
Read, practise, return
1. Read it in context
- RCD TypesInstallation
2. Try recalling, then explore practice
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Follow a topic above to explore how the term is used, then use the learning entry below to find your path.
3. Return to the meaning
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Recall a related term
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A protective device that detects an imbalance between the currents in the live conductors passing through it. In a single-phase circuit this usually means comparing line and neutral current. It disconnects when the residual current meets its operating conditions. A 30 mA RCD can provide additional shock protection, but it does not prevent every kind of electric shock or replace safe isolation.
Compare related terms
Open a meaning to compare its role with Mode 3 charging, or follow its full entry.
RCD — Residual Current Device
A protective device that detects an imbalance between the currents in the live conductors passing through it. In a single-phase circuit this usually means comparing line and neutral current. It disconnects when the residual current meets its operating conditions. A 30 mA RCD can provide additional shock protection, but it does not prevent every kind of electric shock or replace safe isolation.
Read the RCD entryOpen-PEN fault
A break in the PEN conductor of a TN-C-S (PME) supply, out in the distributor's cable. The building's loads then pull its neutral and earth terminal towards the line conductor's voltage, and everything bonded to them follows, while someone outdoors stands on real earth. An RCD won't catch it, which is why BS 7671 sets out specific options for outdoor EV charge points on PME.
Read the Open-PEN fault entrySmart charge point
An EV charge point that can send and receive information and change how it charges in response, for example by moving charging away from peak times. In England, Wales and Scotland, the Electric Vehicles (Smart Charge Points) Regulations 2021 set requirements for them, leaving out public charge points, rapid ones of 50 kW or more and non-smart cables. Those regulations don't extend to Northern Ireland.
Read the Smart charge point entryLoad management
A control that knows the total load and turns down or pauses something like an EV charge point, so the whole installation stays within its limit. It can avoid a supply upgrade. Without a system that really limits it, a charger counts at its full rating in the maximum demand, and a customer's habit of charging overnight doesn't change that.
Read the Load management entryA definition is a start. Using it in a real question is where it sticks.