RCBOs, bidirectional current and plug-in solar in the UK
Plug-in solar changes one assumption people often make about a socket circuit: current is no longer only flowing from the consumer unit towards the load. Generation can push current back towards the board, so the suitability of the protective device matters.
Why does direction matter?
On a normal final circuit, we usually think of energy flowing from the consumer unit out to appliances. With local generation connected to that circuit, current can also flow back towards the consumer unit.
That does not automatically make an RCBO unsuitable. It means the device has to be used within the conditions the manufacturer designed and declared.
The mistake I would avoid: looking at an RCBO, seeing the same current rating as another model and assuming both behave identically with reverse power flow.
What changed with Amendment 4?
BS 7671:2018+A4:2026 was published in April 2026. One of the areas strengthened in the latest edition is the treatment of installations with local generation, storage and bidirectional energy flow.
The IET has specifically highlighted the need for suitable protective devices where energy flow is bidirectional and the importance of how sources are connected relative to RCD protection.
There is a transition period: the previous Brown Book version remains valid until 15 October 2026, after which Amendment 4 becomes the current route for new work.
Does this mean every existing RCBO must be changed?
No. That would be far too broad.
Suitability depends on the exact device, how it is connected and what the manufacturer says. Some devices are explicitly suitable for supply in either direction. Some have marked supply/load terminals or installation requirements that should not be ignored.
If the device data is unclear, I would check the manufacturer's technical information rather than guess from appearance or terminal numbering.
What do line and load markings mean?
If an RCBO is clearly marked LINE/SUPPLY and LOAD, that is a strong indication that connection orientation matters and the manufacturer's instructions should be followed exactly.
Numbered terminals on their own are not enough to prove bidirectional suitability. Different manufacturers use different conventions.
Equally, the absence of obvious LINE/LOAD wording on the front does not automatically prove a device can be supplied in either direction.
What should a homeowner check?
A householder should not remove the consumer-unit cover and start identifying internal wiring arrangements.
The new plug-in solar product instructions are supposed to provide a safe consumer-level check of the protective arrangement. If the consumer unit or device type cannot be identified from the information available without exposing live parts, get a competent person to assess it.
What should an electrician check?
- The exact make and model of the RCBO/RCD.
- Manufacturer instructions and declared direction of supply.
- Whether the generating source is connected on a side of an RCD that creates a prohibited or unsuitable arrangement.
- Whether the device remains suitable for the expected bidirectional current path.
- RCD type and compatibility with the connected equipment.
- Correct circuit identification and final-circuit condition.
Is this only a plug-in solar issue?
No. The same broader issue appears with batteries, hybrid inverters, vehicle-to-home systems and other prosumer installations where energy can flow in more than one direction.
That is one reason Amendment 4 gives this area more attention.
What if the RCBO is not suitable?
Do not try to make the plug-in product “work around” an unsuitable protective arrangement.
If a protective device genuinely needs changing, that becomes electrical installation work. The new self-install product route does not give a householder permission to start modifying the consumer unit.
See when an electrician is needed.
How this fits the final plug-in solar rules
The IPS requires the manufacturer to give the user instructions for checking the consumer unit and residual-current protection. If those checks cannot establish suitability, professional advice is the correct next step.
That is a better approach than internet rules such as “all RCBOs are fine” or “all old RCBOs need replacing”.
My practical summary: bidirectional current is a real design consideration, but it is a device-specific one. Check the actual RCBO and manufacturer data. Do not replace equipment just because somebody on social media says generation always needs a special breaker, and do not assume an unknown device is suitable just because it has never tripped.
Common questions
Is my RCBO automatically bidirectional?
No. Check the exact manufacturer's instructions and product data.
Does plug-in solar reverse current through the RCBO?
It can cause energy to flow from the final circuit back towards the consumer unit, which is why device suitability matters.
Can I change the RCBO myself?
Consumer-unit work is not part of the simple plug-in product installation route and should be carried out by a competent electrician through the appropriate certification/notification process.
Technical guidance only. Protective-device selection must follow the current edition of BS 7671 and the exact manufacturer's instructions.