Solar PV RCD Requirements: Does an Inverter Need a Type B RCD?

Do Solar Inverters Need RCD Protection?

Not every solar PV inverter circuit automatically requires an RCD simply because it contains an inverter.

Whether RCD protection is required depends on the complete installation, including:

• The earthing arrangement
• The protective measure being used
• Cable installation method
• PV inverter design
• Manufacturer instructions
• Distribution-board arrangement
• Whether additional protection is required elsewhere in the circuit

The important distinction is this:

If an RCD is being used to provide protection for the PV AC supply circuit, the correct RCD type then has to be selected for the inverter.

That is where Type B protection becomes particularly important.

When Does a Solar Inverter Need a Type B RCD?

Where an RCD is used for protection of the PV AC supply circuit, Type B protection is required unless the relevant exception for the inverter or installation applies.

Type B becomes the correct choice where:

• The inverter manufacturer specifies Type B protection.
• The inverter does not provide the required separation between its AC and DC sides.
• DC residual current can reach the AC side at a level or waveform requiring Type B detection.
• No manufacturer-supported alternative RCD arrangement applies.

The important point is that Type B is not simply an expensive upgrade from Type A. It has different residual-current detection characteristics.

If those characteristics are required by the inverter, fitting Type A instead is not equivalent protection.

Related guide: What Is a Type B RCD?

👉 Browse Type B RCDs.

Can You Use a Type A RCD With a Solar Inverter?

Potentially, but only where the inverter and installation allow it.

A Type A RCD detects:

• Sinusoidal AC residual current
• Pulsating DC residual current
• Pulsating DC superimposed on a limited smooth DC component within the device specification

A Type B RCD extends detection to smooth DC and other residual-current characteristics that Type A is not designed to cover.

For a PV inverter, Type A may therefore be used where the inverter design provides the necessary separation or where the manufacturer specifically permits a Type A device.

Do not select Type A simply because:

• The inverter is single-phase.
• The installation is domestic.
• The existing consumer unit already contains Type A RCBOs.
• Type B is more expensive.

The inverter specification takes priority over those assumptions.

Related guide: Type A vs Type B RCDs

Why Does DC Residual Current Matter With Solar Inverters?

A solar inverter converts DC electricity from the PV array into AC electricity that can be used within the installation or exported to the grid.

Depending on the inverter topology, faults or leakage on the DC side can potentially influence the residual-current waveform seen on the AC side.

This matters because different RCD types respond to different residual-current waveforms.

If an unsuitable RCD encounters DC residual current outside its intended operating characteristics, its performance can be affected.

That is why RCD selection for power-conversion equipment should be based on the residual current the equipment can actually produce.

What Does AC/DC Separation Mean on a Solar Inverter?

Some inverter designs provide electrical separation between the DC PV side and the AC supply side.

Where the necessary separation is provided, a DC-side fault cannot affect the AC-side protective arrangement in the same way as it could in a non-isolated inverter.

This is one of the reasons the Type B requirement is not universal.

The installer should not try to determine this solely from whether an inverter is described as:

• Transformerless
• Hybrid
• String
• Microinverter
• Single-phase
• Three-phase

Use the manufacturer’s declaration and installation documentation to establish the required RCD arrangement.

Can You Use an RCBO for a Solar Inverter?

Yes, where the correct RCBO is available and suits the PV installation.

An RCBO combines:

• Residual-current protection
• Overload protection
• Short-circuit protection

But specifying “an RCBO” is not enough.

You still need to confirm:

• RCD Type A, F or B characteristic as applicable
• Rated residual operating current
• Current rating
• Trip curve
• Breaking capacity
• Number of poles
• Direction-of-current requirements
• Board compatibility

This last point is increasingly important on generating circuits because current can flow from the inverter towards the installation rather than only from the grid towards a load.

Does a Solar PV Circuit Need a Bidirectional RCBO?

Solar PV is a generating circuit, so the direction of energy flow through a protective device needs to be considered.

Some protective devices are suitable for current flow in either direction. Others have defined supply and load terminals or other manufacturer restrictions.

For a PV circuit, confirm that the selected MCB, RCBO or other protective device is suitable for the direction of current flow expected in the installation.

Do not assume every RCBO is automatically bidirectional simply because it physically fits the consumer unit.

The product markings and manufacturer’s data should confirm suitability.

Single-Phase vs Three-Phase Solar Inverter RCDs

The inverter phase configuration also affects the protective-device arrangement.

Where Type B protection is required:

• A single-phase inverter commonly uses an appropriate 2-pole Type B RCD arrangement.
• A three-phase and neutral inverter commonly requires an appropriate 4-pole Type B RCD arrangement.

However, pole count should be selected from the actual inverter and supply configuration rather than simply assuming every three-phase system contains a neutral.

Also confirm:

• Inverter current rating
• Manufacturer’s protective-device rating
• Required residual-current sensitivity
• Whether neutral switching is required
• Short-circuit protection
• Board compatibility

👉 Browse 3-phase RCDs and three-phase boards and accessories.

Check Upstream RCD Protection as Well

The RCD directly protecting the inverter circuit is not always the only device that matters.

If the PV circuit is connected downstream of another RCD, the upstream device must also be considered.

An unsuitable upstream RCD can potentially be affected by residual-current characteristics produced by inverter equipment, even if a more suitable device has been fitted directly on the PV circuit.

Review:

• Existing RCCBs protecting groups of circuits
• Upstream RCBOs
• Main or sub-board RCDs
• RCD type
• Selectivity
• Standing leakage current
• Manufacturer instructions

What About Hybrid Solar and Battery Inverters?

Hybrid and battery systems need additional consideration because the power-conversion equipment may operate in more than one mode.

Depending on the system, power may flow:

• From the grid to the installation
• From the PV array to the installation
• From the PV array to the grid
• Into the battery
• Out of the battery
• From local generation to selected loads during island operation

This means the designer may also need to consider:

• Bidirectional protective devices
• Island-mode operation
• Neutral-earth referencing
• Automatic disconnection of supply in each operating mode
• Local earth electrodes where required
• RCD operation in connected and island modes

A simple grid-tied solar-inverter RCD rule should therefore not be applied blindly to a hybrid battery installation.

Related guide: Do Battery Storage Systems Need a Type B RCD?

Does Solar PV Need Surge Protection as Well?

RCD protection and surge protection perform completely different functions.

• RCD: responds to residual-current faults.
• SPD: limits transient overvoltages.

A Type B RCD does not replace the need to assess surge protection on a solar PV installation.

PV systems can require surge protection on:

• The AC side
• The DC side
• Both sides of the inverter

The correct arrangement depends on the system design, cable routing, lightning-protection arrangement and applicable PV requirements.

👉 Browse surge protection devices.

How to Choose an RCD or RCBO for a Solar Inverter

1. Identify the exact inverter. Record the manufacturer and model.
2. Read the current installation instructions. Look specifically for RCD requirements.
3. Establish whether RCD protection is required. Determine what protective function it is providing.
4. Check AC/DC separation. Establish whether the inverter provides the relevant separation.
5. Select the RCD type. Use Type B where required; do not substitute Type A without manufacturer-supported justification.
6. Confirm residual-current sensitivity. Use the value required by the equipment and installation.
7. Check single or three-phase configuration. Select the appropriate number of poles.
8. Select the current rating. Coordinate with the inverter output and cable.
9. Check trip curve. Where an RCBO is used, confirm the required overcurrent characteristic.
10. Check breaking capacity. Ensure the protective device is suitable for prospective fault current.
11. Check current direction. Confirm that the protective device is suitable for the generating circuit.
12. Review upstream RCDs. Check the complete protection hierarchy.
13. Assess surge protection separately. RCD selection does not address transient overvoltage.
14. Check hybrid or island modes. Where battery storage is included, verify protection in every operating mode.

Solar PV Circuit Protection

• Type B RCDs
• Type A RCDs
• 3-Phase RCDs
• RCBOs
• Surge Protection Devices
• Solar Combiner Boxes
• Consumer Units
• Three-Phase Boards & Accessories

Check the inverter manufacturer’s requirements before ordering the RCD type, residual-current rating, current rating, pole configuration or protective-device arrangement.

Solar PV RCD FAQs

Do solar inverters need RCD protection?

Not automatically in every installation. Whether an RCD is required depends on the circuit design and protective measures being used. Where an RCD protects the PV AC supply circuit, its type must be suitable for the inverter.

Do solar inverters need a Type B RCD?

Where an RCD is used on the PV AC supply circuit, Type B is normally required unless the inverter or installation provides the relevant separation between AC and DC, or the inverter manufacturer states that Type B is not required.

Can I use a Type A RCD for solar PV?

Yes, where the inverter manufacturer and the installation design specifically permit Type A protection. It should not be assumed suitable without checking the inverter documentation.

What RCD should I use for a solar inverter?

Use the type specified by the inverter manufacturer and required by the installation. Depending on the equipment, this may be Type A or Type B, with the appropriate current rating, sensitivity and number of poles.

What RCBO should I use for solar PV?

Select an RCBO whose RCD type, residual-current sensitivity, current rating, trip curve, breaking capacity, direction-of-current capability and pole configuration match the inverter and circuit.

Does a solar inverter need a 30 mA RCD?

Do not assume every inverter requires 30 mA protection. The residual-current rating depends on why the RCD is required and what the inverter manufacturer specifies.

Does a single-phase solar inverter need a 2-pole RCD?

Where an RCD is required and line and neutral need simultaneous switching, a suitable 2-pole arrangement is common. Follow the inverter and system requirements.

Does a three-phase solar inverter need a 4-pole Type B RCD?

Where the inverter is three-phase and neutral and Type B protection is required, a suitable 4-pole Type B device is commonly used. Check whether the particular inverter uses and requires switching of neutral.

Why can DC current affect an RCD?

Different RCD types are designed to respond to different residual-current waveforms. Smooth DC outside the capability of an unsuitable RCD can affect its ability to operate correctly.

Does an inverter with galvanic separation need Type B?

Not necessarily. Appropriate separation between the AC and DC sides is one circumstance in which the standard Type B requirement for the PV AC circuit may not apply.

Can I use Type AC on a solar inverter?

Do not use Type AC unless the inverter and installation characteristics explicitly make it suitable. Power-conversion equipment can produce residual-current waveforms outside the capability of Type AC devices.

Do solar RCBOs need to be bidirectional?

The protective device must be suitable for the direction of current flow in the generating circuit. Check the manufacturer’s markings and data rather than assuming every RCBO is suitable in both directions.

Does a hybrid solar inverter use the same RCD arrangement?

Not necessarily. Hybrid and battery systems may operate in multiple power-flow and island modes, so RCD, earthing and automatic-disconnection requirements should be checked for every mode of operation.

Does solar PV need surge protection?

Surge protection is assessed separately from RCD protection. Depending on the PV installation, SPDs may be required on the AC side, DC side or both.

Does Your Solar Inverter Need a Type B RCD?

The answer depends on the inverter.

Where an RCD is protecting the PV AC supply circuit, Type B is the normal requirement unless:

• The inverter or installation provides the relevant separation between AC and DC, or
• The inverter manufacturer specifically states that Type B is not required.

Before ordering protection, confirm:

• Whether the circuit requires an RCD
• Exact inverter make and model
• Manufacturer’s RCD specification
• AC/DC separation
• RCD type
• Residual-current sensitivity
• Single or three-phase configuration
• Pole count
• Current rating
• RCBO direction-of-current suitability
• Upstream RCD compatibility
• Surge protection
• Hybrid or island-mode requirements where applicable

👉 Compare our Type B RCDs, 3-phase RCDs, surge protection devices and solar combiner boxes.