by ericmark »
Sun Feb 05, 2023 11:22 am
Solar panels generate DC, which is turned into AC with the grid tie inverter, there is a possibility under fault conditions DC could pass, and DC can freeze type AC RCD's.
The type A can handle up to 6 mA and some inverters have a detection unit built in which will auto should down if 6 mA is exceeded. But they can't guarantee to trip with any DC. So the RCD for the solar panel needs to be type A or B the type B will handle more than 6 mA but are very expensive, and not seen any as single module width RCBO's which is a RCD and MCB combined.
Also I think the rules say solar panels should not share the RCD with other items, which makes sense as it is supplying power, so if shared with other items they would be powered without protection.
The solar panel installer has to design the system, and he could well use a dedicated enclosure for the solar panels, and not connect to your existing consumer unit, or he could swap the existing consumer unit for a modern ones with RCBO's and SPD (surge protection device) the latter protects direct connected electronics from spikes on the supply.
There has been a lot of talk about AFDD's and SPD's as to if really required, after all back in the 60's we did not even have RCD's, but we did not use front loading VCR's with switch mode power supplies or LED bulbs back then, and the switch mode power supply is now in many of our modern appliances.
Each edition of the wiring regulations has the date at which designs must comply, note design date not installation date, so some thing designed before 1966 can still be repaired and used, and parts replaced, but the question arises if a light fixture designed for tungsten lamps can be used with LED, as the design has changed?
OK being pedantic, but the point is modern appliances can cause old RCD's to freeze, and the procedure is still to test the RCD with no load, so one would not know it would not work once the solar panel or EV charging point is in use.
I have all type AC RCBO's and I have no intention on changing them, I take the attitude the RCD part will still trip at some point even with DC on the supply, and it is extra protection not the only protection, so with a TN supply not really worried.
However working in some one else's home, I need to comply with the regulations so I would have to say sorry that consumer unit needs changing so my new design complies, there are likely other ways around the problem, but for the cost, not really worth doing.
