Type A vs Type B RCDs: What Is the Difference?

What Is the Difference Between Type A and Type B RCDs?

The key difference is the range of residual-current waveforms each device is designed to detect.

Type B includes the protection characteristics associated with Type A, but its wider capability does not mean it should automatically be used on every circuit.

The correct type should be selected from the equipment characteristics, manufacturer instructions and installation design.

👉 Compare Type A RCDs and Type B RCDs.

What Is a Type A RCD?

A Type A RCD is designed to detect:

• Sinusoidal alternating residual current
• Pulsating DC residual current
• Pulsating DC residual current superimposed on a smooth DC component within the device’s specified limits

Type A is widely used with modern single-phase equipment containing electronic controls, rectifiers and switch-mode power supplies.

Potential applications include:

• General socket circuits
• LED lighting and electronic lighting controls
• Washing machines and domestic appliances
• Boilers and electronic heating controls
• Induction cooking equipment
• IT equipment and power supplies
• EV charging equipment where the required DC fault protection is provided separately

These examples do not make Type A universally suitable. The exact equipment and manufacturer’s instructions must still be checked.

What Is a Type B RCD?

A Type B RCD provides wider residual-current detection than Type A.

Depending on its applicable product standard and manufacturer specification, it is designed to detect:

• Sinusoidal AC residual current
• Pulsating DC residual current
• Smooth DC residual current
• Residual currents containing multiple frequencies within the device’s specified range

Type B is considered where equipment contains three-phase rectification, variable-frequency drives, inverters or other power electronics capable of producing smooth DC residual current.

Potential applications include:

• Some EV charging installations
• Some photovoltaic inverter installations
• Battery energy-storage systems
• Variable-speed drives
• Industrial machinery
• UPS systems
• Lifts and escalators
• Welding equipment
• Some three-phase inverter-driven systems

The word some matters.

Many products include internal monitoring, separation or DC detection that allows a different upstream RCD arrangement. The equipment manufacturer’s instructions should determine whether Type B is required.

👉 Browse 2-pole and 4-pole Type B RCDs.

Where Does a Type F RCD Fit?

Type F sits between Type A and Type B in terms of residual-current capability.

It is intended for certain single-phase frequency-controlled equipment and offers:

• Type A residual-current characteristics
• Defined mixed-frequency capability
• Improved resistance to certain unwanted tripping conditions
• Suitability for some single-phase variable-speed equipment where specified

Potential applications can include certain:

• Air-conditioning systems
• Heat pumps
• Washing machines
• Dishwashers
• Power tools
• Single-phase inverter-driven appliances

Type F should not be selected merely as a cheaper substitute for Type B. It must be suitable for the residual-current characteristics of the exact equipment.

Likewise, equipment needing Type F should not automatically be placed on Type A solely because both cover pulsating DC.

When Should You Use Type A or Type B?

RCD selection should begin with the connected equipment, not the name of the circuit.

These are selection starting points, not universal rules.

The equipment instructions take priority over a broad assumption based on whether the load is described as an EV charger, inverter, heat pump or solar system.

Does an EV Charger Need Type A or Type B?

An EV charger does not automatically require Type B.

For Mode 3 charging:

• Where suitable protection against DC residual current is incorporated into the EV charging equipment, a Type A or Type F RCD may be used.
• Where that DC protection is not provided, a Type B RCD is required.

The DC protection is commonly provided through an RDC-DD designed for the EV charging application.

The RCD must also disconnect all live conductors and meet the applicable EV charging requirements.

Full EV guide: Type A vs Type B RCDs and RCBOs for EV Chargers

This general article should not be used to size the EV RCBO or select the charger circuit arrangement. Those decisions depend on the exact charger and installation design.

Does a Heat Pump Need Type A or Type B?

Heat-pump RCD selection varies between manufacturers and equipment designs.

A modern heat pump may contain:

• An inverter-driven compressor
• Variable-speed motors
• Electronic expansion controls
• Pumps and auxiliary heaters
• EMC filters
• Single-phase or three-phase power conversion

Depending on the internal design, the manufacturer may specify Type A, Type F, Type B or no upstream RCD unless required by the wider installation.

Do not assume that every inverter heat pump needs Type B. Equally, do not assume Type A is sufficient without checking the current technical documentation.

Related guide: Type A vs Type B RCDs for Heat Pumps

What Is RCD Blinding?

RCD blinding describes a situation where a DC component affects the magnetic core or sensing system of an unsuitable upstream RCD.

The device may become desensitised and fail to operate within its intended time, or in some circumstances may not operate as required.

This risk is particularly associated with using an RCD that is not designed for the residual-current waveform produced by the connected equipment.

Examples include:

• Using Type AC where pulsating DC components are present.
• Using Type A where uncontrolled smooth DC above its permitted level may occur.
• Installing an unsuitable RCD upstream of equipment or downstream devices producing DC residual current.

Selection must therefore account for the entire RCD hierarchy, not only the final protective device nearest the equipment.

What Do Type A and Type B RCD Symbols Look Like?

The symbol printed on the front or side of the RCD identifies its residual-current type.

• Type AC: Normally marked with a sinusoidal waveform.
• Type A: Normally marked with a sinusoidal waveform and a pulsating rectified waveform.
• Type F: Carries additional markings identifying its mixed-frequency characteristics.
• Type B: Carries waveform markings indicating its wider AC, pulsating DC and smooth DC capability.

The exact graphic presentation can vary according to the applicable standard and manufacturer.

Do not confuse the residual-current symbol with:

• B or C overcurrent curves
• Current rating, such as 40 A or 63 A
• Residual sensitivity, such as 30 mA or 100 mA
• S-type time-delay marking
• Two-pole or four-pole configuration

For example, a device can be described as a:

C40 Type A 30 mA RCBO

This means:

• C curve overcurrent characteristic
• 40 A rated current
• Type A residual-current detection
• 30 mA rated residual operating current

What Is the Difference Between an RCD, RCCB and RCBO?

RCD is the general term for a residual-current device.

Type A or Type B can describe an RCCB or an RCBO.

However, Type B RCBO availability is more limited than Type B RCCBs, particularly in some current ratings, pole configurations and board systems.

Where a Type B RCCB is used, separate overcurrent protection must be correctly coordinated.

What Are the Main BS Numbers for RCDs?

The applicable product standard depends on the device and application.

Common examples include:

• BS EN 61008-1: RCCBs without integral overcurrent protection for household and similar applications
• BS EN 61009-1: RCBOs with integral overcurrent protection for household and similar applications
• BS EN 62423: Additional requirements for Type F and Type B RCDs
• BS EN 60947-2: Certain circuit breakers and residual-current devices for industrial applications
• BS IEC 62955: RDC-DD equipment used for Mode 3 EV charging applications

The standard number alone does not confirm that the device is appropriate.

Also verify:

• Residual-current type
• Rated current
• Rated residual operating current
• Time-delay characteristic
• Breaking and short-circuit capacity
• Poles and switching arrangement
• Frequency and voltage rating
• Assembly or consumer-unit compatibility

How Do You Choose the Correct RCD Type?

1. Identify the equipment. Obtain the current manufacturer documentation.
2. Confirm whether an RCD is required. Establish whether it is providing fault protection, additional protection, fire-risk protection or equipment protection.
3. Identify the possible residual-current waveforms. Check for AC, pulsating DC, smooth DC and mixed-frequency components.
4. Select Type A, F or B. Follow the equipment and installation requirements.
5. Review upstream RCDs. Confirm the hierarchy cannot be blinded by downstream DC residual current.
6. Choose the device format. Decide whether an RCCB, RCBO or equipment-integrated arrangement is appropriate.
7. Select the sensitivity. Confirm whether 10 mA, 30 mA, 100 mA, 300 mA or another value is required.
8. Check poles and disconnection. Confirm which live conductors must be switched.
9. Check the current rating. Coordinate an RCCB with suitable overcurrent protection.
10. Confirm product standards and compatibility. Verify the device suits the board, supply and application.

Browse Type A and Type B Protection

• Type A RCDs
• Type A RCBOs
• Mini Type A RCBOs
• High-Immunity RCBOs
• Type B RCDs
• B+ Type RCDs
• Three-Phase RCDs
• All RCDs
• All RCBOs

Check the full specification rather than selecting by Type A or Type B alone. Current rating, residual sensitivity, time delay, pole count and equipment compatibility remain separate requirements.

Type A vs Type B RCD FAQs

What is a Type A RCD?

A Type A RCD detects sinusoidal AC and pulsating DC residual currents. It is commonly used for modern single-phase equipment containing electronic controls.

What is a Type B RCD?

A Type B RCD provides wider detection, including smooth DC residual current and additional frequency characteristics within its product specification.

What is the main difference between Type A and Type B?

Type B can detect smooth DC residual current that a standard Type A device is not designed to detect.

Can Type A be used instead of Type B?

Only where the connected equipment and installation do not require Type B characteristics. Manufacturer instructions and residual-current data should confirm the selection.

Can Type B be used instead of Type A?

Potentially, because Type B provides wider residual-current detection. However, cost, frequency behaviour, upstream coordination and manufacturer requirements must still be considered.

Is Type B always better than Type A?

No. It has wider detection characteristics, but the correct device is the one suited to the equipment and circuit. Wider capability alone does not guarantee better overall coordination.

Does every EV charger need Type B?

No. Where the EV charger contains suitable DC residual-current protection, a Type A or Type F RCD may be used. Without that protection, Type B is required.

Does every heat pump need Type B?

No. Heat-pump requirements vary by manufacturer and model. Type A, Type F or Type B may be specified.

Does every solar inverter need Type B?

No. The inverter design, separation and manufacturer instructions determine the RCD type where an RCD is required.

Does every battery-storage system need Type B?

No. Selection depends on the inverter, topology, protection incorporated into the equipment and manufacturer requirements.

What is Type F?

Type F is intended for certain single-phase frequency-controlled equipment. It provides Type A characteristics plus defined mixed-frequency capability.

What causes RCD blinding?

A DC component outside the capability of the device can desensitise an unsuitable RCD and affect its ability to operate correctly.

What does the Type A RCD symbol mean?

It normally combines a sinusoidal waveform with a pulsating rectified waveform, indicating AC and pulsating DC detection.

What does the Type B RCD symbol mean?

It includes markings identifying its wider capability for AC, pulsating DC and smooth DC residual currents.

Is a Type B RCBO the same as a B-curve RCBO?

No. Type B residual-current detection and a B-curve overcurrent characteristic are different classifications. A device description must state both separately.

What is the difference between an RCD and RCBO?

RCD is the general device category. An RCBO combines residual-current and overcurrent protection, while an RCCB requires separate overcurrent protection.

What BS number applies to a Type B RCD?

Type B devices for household and similar applications are commonly associated with BS EN 62423 alongside the relevant base RCCB or RCBO standard. Confirm the complete product marking.

Are Type A RCDs mandatory for domestic circuits?

Not universally. The RCD type must be selected according to the connected equipment and residual-current characteristics. Type AC is now restricted to qualifying fixed equipment known to contain no DC component.

Can a Type B RCD be two pole or four pole?

Yes. Two-pole devices are used for suitable single-phase arrangements, while four-pole devices are commonly used where all conductors of a three-phase system require switching.

Why are Type B RCDs more expensive?

They require more complex sensing and electronic or magnetic arrangements to detect a wider range of residual-current waveforms.

Should You Choose Type A or Type B?

Choose Type A where the equipment produces residual currents within Type A capability and no wider device is specified.

Choose Type B where smooth DC or other residual-current characteristics outside Type A capability may occur, or where the manufacturer requires it.

Before ordering, confirm:

• The exact connected equipment
• The possible residual-current waveforms
• The manufacturer’s required RCD type
• Any integrated DC detection or separation
• Upstream RCD compatibility
• RCCB or RCBO format
• Current rating and residual sensitivity
• Time-delay requirements
• Pole count and conductor disconnection
• Applicable product standards

👉 Compare Type A RCDs, Type B RCDs and the wider RCD range.