Are RCDs Legally
Required?
The legal status of RCD protection in UK domestic installs in 2026. What BS 7671 Section 411 actually says, where 30mA RCDs are required, where they are recommended plus the few places they are not needed.
Yes, on most circuits. BS 7671:2018+A2:2022 requires 30mA RCD additional protection on socket outlets in dwellings, on cables concealed in walls less than 50mm deep plus on circuits supplying mobile equipment for outdoor use. Compliance is enforced through Part P of the Building Regulations. An existing installation without RCDs is not retrospectively illegal but will fail an EICR if the missing protection presents a safety risk. New installs plus any circuit alteration must include RCD protection where the regulation requires it.
Three figures
worth knowing
Trip Threshold
The maximum residual current allowed before an RCD must disconnect for additional shock protection on a domestic circuit.
BS 7671 Section
Section 411.3.3 plus 411.3.4 set out where RCDs are required on UK domestic installs. Section 415 covers additional protection.
17th Edition
RCD additional protection became required on most domestic circuits with the 17th Edition of BS 7671. Strengthened in every amendment since.
Where RCD protection is
required, advised plus exempt
BS 7671 splits its RCD requirements across three broad categories. Most circuits in a UK home land in the first category. The other two are narrower.
Most circuits in dwellings
Socket outlets up to 32A intended for use by ordinary persons, cables concealed in walls or partitions less than 50mm deep, mobile equipment used outdoors plus all final circuits in bathrooms plus shower rooms. This covers virtually every domestic circuit. 30mA RCD protection is mandatory on a new install or alteration.
Socket circuits in HMOs plus HRRBs
In addition to RCD protection, socket circuits in licensed HMOs, higher-risk residential buildings, care homes plus purpose-built student accommodation also require AFDD protection. The AFDD device on the same circuit normally provides the RCD function as well.
All other final circuits
Circuits that fall outside the strict 411.3.3 plus 411.3.4 wording (some hard-wired appliance circuits, circuits feeding equipment used only by skilled persons) are still typically protected by RCD or RCBO on modern installs. Industry best practice now treats RCD protection as the default across the entire board.
Specific exempt circuits
BS 7671 does allow some exemptions. Examples include socket outlets specifically labelled for use only by skilled persons, certain dedicated appliance circuits where loss of supply would cause greater danger than absence of additional protection (medical equipment, freezer-only circuits in commercial settings) plus certain SELV or Class II protected installations. Exemptions are narrow plus must be documented on the EIC.
RCD requirements have tightened steadily since 2008
The legal force behind RCD protection in UK domestic installs comes from a combination of BS 7671 plus Part P of the Building Regulations. BS 7671 sets the technical requirement. Part P makes that requirement legally enforceable on dwellings in England plus Wales. Equivalent provisions apply in Scotland through the Building (Scotland) Regulations.
The two BS 7671 clauses that homeowners encounter directly are 411.3.3 plus 411.3.4. The first requires 30mA RCD protection on socket outlets up to 32A intended for use by ordinary persons. The second, added in Amendment 2 of the 18th Edition, requires 30mA RCD protection on socket outlets in dwellings as a general principle. Together these two clauses cover nearly every circuit in a UK home.
What "additional protection" means
The phrase "additional protection" is important. BS 7671 splits protection against electric shock into three layers:
- Basic protection. Insulation plus enclosures preventing contact with live parts under normal operation.
- Fault protection. Automatic disconnection of supply (ADS) under fault conditions, primarily through MCBs plus the earthing arrangement.
- Additional protection. 30mA RCD that disconnects the circuit if a person comes into direct contact with a live conductor (for example by inserting a metal object into a socket). This is the third defensive layer that BS 7671 mandates on most modern circuits.
An RCD is not a substitute for the first two layers. It is the third layer designed for the specific scenario where the first two have failed plus a person is in physical contact with a live conductor. The 30mA threshold reflects the maximum let-through current considered survivable for a healthy adult during the brief disconnection time.
What about existing installations without RCDs?
This is where the legal picture nuances. An existing installation that pre-dates the 17th Edition is not retrospectively illegal just because it has no RCD protection. Many UK homes still have MCB-only boards from the late 1990s or 2000s. These boards were compliant when fitted plus continue to operate legally until something triggers replacement.
What changes that picture is any of the following:
- An EICR. The lack of RCD protection on an existing installation is normally coded C2 (potentially dangerous) on an EICR. C2 makes the report Unsatisfactory which forces remedial work.
- An alteration or addition. Adding any new circuit, replacing the consumer unit, fitting an EV charger or a shower triggers a duty to bring the affected circuits up to current BS 7671. RCD protection becomes mandatory at that point.
- A landlord context. The 2020 Electrical Safety Standards Regulations require landlords to hold a Satisfactory EICR. An MCB-only board is unlikely to pass.
RCD types: AC, A, F, B
An RCD is not just an RCD. BS 7671 plus the IEC standards split residual current devices into types based on the kind of fault current they can detect. The type that matters depends on what is connected to the circuit:
- Type AC detects sinusoidal alternating residual currents only. Suitable for resistive plus inductive loads. The original RCD type. Now considered too limited for circuits feeding modern electronic loads.
- Type A detects AC plus pulsating DC residual currents. The current default for most domestic circuits. Required for most LED lighting, washing machines, modern EV chargers plus solar inverters.
- Type F detects AC, pulsating DC plus mixed-frequency residual currents. Used where variable frequency drives are present (some heat pumps, some commercial drives).
- Type B detects all of the above plus smooth DC residual currents. Required for some EV chargers without internal DC fault detection plus for most three-phase variable speed drives.
Specifying the wrong RCD type for a connected load can leave that load without effective shock protection. This is one of the practical reasons EV charger installs sometimes trigger a full board upgrade: the existing Type AC RCDs in older boards are not compatible with the DC fault characteristics of a modern EV charger.
Four moments that
tightened the rule
UK RCD requirements have moved through four legislative steps. Each tightened the protection one notch further.
Selective RCD Use
RCDs required on bathroom plus shower circuits plus on outdoor sockets only. Most other domestic circuits used MCBs without additional protection.
17th Edition Adopted
RCD additional protection extended to most domestic circuits. Triggered the move from MCB-only boards to dual RCD plus full RCBO designs across the UK.
18th Edition Published
BS 7671:2018 strengthened RCD requirements around concealed cables (less than 50mm depth) plus refined Type A as the default for most domestic loads.
Amendment 2 Mandates
Section 411.3.4 added making 30mA RCD protection mandatory on socket outlets in dwellings as a general rule. Effectively closed the remaining gap.
Four practical takeaways
Old does not always mean illegal
An existing MCB-only board is not retrospectively illegal. It only becomes a problem at the next EICR, alteration or new tenancy.
RCD type matters
Type A is the modern default. Type AC is now too limited for most domestic loads. Type B is needed for some EV chargers plus three-phase drives.
Test the RCD every six months
Press the test button on every RCD or RCBO. Each must trip instantly. The label on the device confirms the recommended test interval.
Adding any circuit triggers compliance
Adding an EV charger, fitting a new shower or rewiring a kitchen all bring the affected circuits up to current BS 7671. RCD protection becomes mandatory.
Consumer Unit Upgrades in Milton Keynes
C-Lec Electrical fits BS 7671 compliant consumer units with full 30mA RCD protection across Milton Keynes, Bedford plus the surrounding Bedfordshire area. Type A RCBOs as standard. Type B available for EV charger installs.
For the wider context on consumer units, RCBOs, AFDDs plus the regulations behind all of this, head back to our full guide to consumer units where every common question is answered in one place.
Back to the Consumer Units Guide
This article sits inside our complete Consumer Units knowledge base. The hub covers everything from board types plus RCBOs through to landlord requirements plus BS 7671 wiring regulations.
More on consumer
unit protection
If you have not seen a split-load RCD board explained, our walkthrough on what is a dual RCD board sets out how the older split-load design works. To understand the modern alternative where every circuit gets its own RCD, the explainer on what is an RCBO board covers full RCBO protection. For the broader regulatory picture, the dedicated consumer unit wiring regulations guide breaks down every BS 7671 section that applies. If you need a board with full RCD protection fitted in Milton Keynes or Bedford, our consumer unit upgrades service page is the fastest route to a quote.