Type A RCBO Explained

Type A RCBOs Explained: What They Are, Why You Need Them & What’s Next (2025 Update)

Type A RCBOs – Residual Current Circuit Breakers with Overcurrent protection – are a must in modern electrical installations. They protect against earth faults, overloads, and are now the standard under UK wiring regulations for most residential and commercial circuits.

In this comprehensive guide, you’ll learn:

What a Type A RCBO does
Why Type A is preferred over Type AC
Where Type B RCBOs are used
What to watch out for when reading “Type B” on listings
What’s coming soon (hint: real Type B RCBOs from Live Electrical!)

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⚙️ What is a Type A RCBO?

A Type A RCBO is a device that:

Combines RCD protection (earth leakage) and MCB protection (overcurrent)
Detects both AC and pulsating DC leakage currents (up to 6 mA)
Trips when it senses an imbalance or overload, providing life-saving disconnection

It’s ideal for:

Circuits with electronics (chargers, washing machines, LED drivers)
Socket outlets
Lighting circuits
Showers and cookers

❌ Is There Any Situation Where You Must Not Use Type A and Must Use Type AC?

No — there is no situation in modern UK wiring regulations where Type AC is required instead of Type A.

Type A can do everything Type AC can, plus more.

Type A vs Type AC vs Type B RCBOs

Type	Detects	Common Usage
Type AC	Pure AC leakage	Obsolete – no longer recommended
Type A	AC + pulsating DC	Most modern home & office circuits
Type B	All above + smooth DC	EV chargers, solar PV, UPS, drives

BS 7671:2018 recommends Type A as the minimum for final circuits with electronics. Type AC is now discouraged.

Clearing Up the Confusion: “Type B RCBO” vs “Curve B RCBO”

Many people confuse “Type B RCBO” with Curve B tripping characteristics. These are not the same.

Type B RCBO (RCD Type) → Detects smooth DC leakage.
Curve B (MCB Trip Curve) → Tripping at 3–5× rated current. Standard in domestic installs.

⚠️ A product listed as “10A Type B RCBO” could just be Curve B, not a true Type B RCD. Always check the datasheet.

️ We’ve added a screenshot example of this confusion from a competitor listing (not linked to avoid promoting them) – See below:

EV Chargers & PV: Why Type B Is Becoming Necessary

EV Chargers often leak smooth DC. If the charger lacks built-in DC detection (RDC-DD), a true Type B RCBO is required.
Solar PV inverters also emit complex leakage currents. Many setups now require Type B protection, particularly under IEC 62109-1 and BS 7671 Section 712.

Coming Soon: Type B RCBOs from Live Electrical

We’re excited to announce that we’ll soon be stocking genuine Type B RCBOs from Live Electrical. These detect AC, pulsating DC, and smooth DC leakage, and are perfect for:

EV circuits
PV systems
Specialist industrial installations

Launching soon – stay tuned!

Frequently Asked Questions

Section 1: General & Technical RCBO Questions

❓ What does RCBO stand for?

Residual Current Circuit Breaker with Overcurrent protection.

❓ What is a Type A RCBO?

It combines RCD and MCB protection, detecting AC and pulsating DC leakage while also protecting against overloads and short circuits.

❓ Is a Type A RCBO better than an RCD?

It depends on the application.
Type A RCBOs provide both earth leakage and overcurrent protection in a single device. This makes them ideal for individual circuit protection, especially in RCBO-based consumer units.
A standalone RCD only detects earth leakage and requires additional MCBs. In some grouped or legacy systems, RCDs are still used, but RCBOs offer better selectivity and reduced nuisance tripping.

❓ What is the difference between Type A and Type AC RCBO?

Type A detects AC and pulsating DC leakage. Type AC only detects pure AC — and is now considered outdated for modern installations.

❓ What’s the difference between Type A and Type B RCBO?

Type A detects AC + pulsating DC faults. Type B detects all of the above plus smooth DC, making it essential for EV chargers and solar PV systems.
Note: In this context, “Type B” refers to the RCD type, not the MCB tripping curve. Always check the datasheet to avoid confusion with Curve B breakers.

❓ Is “Type B RCBO” the same as “Curve B RCBO”?

No. “Type B” can refer to MCB tripping curve (common) or RCD type (rare). Always check the product spec.

❓ Are RCBOs bidirectional?

Some are, but not all. Check manufacturer specs to ensure correct installation orientation.

❓ Do RCBOs trip on overload?

Yes, the MCB part of the RCBO protects against overloads and short circuits.

❓ Can RCBOs be reset?

Yes. After clearing a fault, simply switch it back on.

❓ Do RCBOs fail?

Yes. Like any protective device, they can degrade. Regular testing is recommended.

️ Section 2: Installation, Use & Safety Questions

❓ Can Type A RCBOs be used for sockets?

Yes. They’re ideal for general-purpose circuits and modern electronic loads.

❓ What type of RCBO for showers?

Type A is recommended — showers often include electronic controls that may emit pulsating DC.

❓ Do RCBOs need double-pole switching?

Not always.
Double-pole (or SP&N) RCBOs are required in TT systems and recommended for EV, solar, and backup power circuits. In TN-C-S systems, single-pole RCBOs are allowed — but most modern RCBOs now include a switched neutral by default, offering added safety and isolation.

❓ Can I use an RCBO as a main breaker?

Not typically. Use a main switch and RCBOs per circuit for full protection and selectivity.

❓ What type of RCBO is needed for EV chargers?

Type A if the charger has built-in DC detection
Type B if the charger does not

❓ What type of RCBO is used for solar panels?

A Type B RCBO is typically required for solar PV systems to detect smooth DC leakage from inverters. If the inverter guarantees no DC leakage, a Type A RCBO may be used — but only if confirmed by the manufacturer.

❓ How do I test an RCBO?

Press the “T” button. If the unit trips, it’s working. If not, it may be faulty.

❓ When should I upgrade from Type AC to Type A?

If your circuit powers anything with electronics — LEDs, chargers, appliances — you should upgrade.

❓ When did Type A RCBOs become standard in the UK?

Type A RCBOs were first recommended in the 18th Edition of BS 7671 in July 2018, especially where electronic loads or DC leakage were possible.
However, it wasn’t until Amendment 2 (28 March 2022) that the regulations explicitly restricted the use of Type AC RCDs to fixed equipment with no chance of DC components (Regulation 531.3.3).

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References

Martindale Electric – Leakage Current Testing Guide
BS 7671:2018 + A2:2022 Wiring Regulations – IET
BEAMA – “Selection of RCDs for Modern Installations” (2019)
Electrical Safety First – RCD Report (2020)
The-Regs.co.uk: Type B RCDs Explained
Sparkyninja – Type A vs AC in Modern Loads
Schneider – Type B Application White Paper