• • • HAZARDOUS AREA EQUIPMENT • • •
Understanding RCD considerations for Solar PV,
Battery Storage and EV Chargers By Steve Donovan, Head of Technical UK & Ireland, Segen
R
esidual Current Devices (RCDs) are critical components in electrical installations, providing protection against electric shocks and fire risks caused by earth leakage. However, when it comes to installing renewable technologies like solar PV, battery storage systems and EV chargers, choosing the correct RCD and knowing whether you need one at all can be more complicated than it seems. In this article, Steve Donovan, explores the nuances of RCD considerations for these systems and offers guidance on choosing the right type of protection.
Do you really need an RCD? RCDs have become so commonplace nowadays that the decision to install RCCBs (residual current circuit breakers) and more recently RCBOs (residual current breakers with overcurrent protection) is almost automatic. However, there are specific circumstances that mean that you
don’t need an RCD at all. The benefits of not installing an unnecessary RCD include cost and time savings, as well as the prevention of nuisance tripping.
When it comes to renewable energy systems, the decision to install an RCD isn’t always straightforward. For example, if the main fuseboard and solar inverter are installed in the same area (like a garage or plant room), and the inverter’s supply cabling is fully visible from the origin to the inverter, then it’s possible to argue that an RCD isn’t necessary. The reasoning is that the risk of the cable being damaged or disturbed is low when it’s visibly secured along a wall or inside surface trunking. Interestingly, Section 8.8 of the IET Code of
Practice (COP) for Grid Connected Solar PV confirms there is no fundamental requirement to install an RCD on the circuit feeding the inverter(s). In fact, it recommends designing
systems so that inverters are not fed by an RCD, as this can prevent unnecessary tripping in the event of minor faults. However, EV chargers are a different case, and an RCD is always required for these installations.
Selecting the right type of RCD Once you’ve determined that an RCD is necessary for your installation, the next step is choosing the right type. Historically, the most common RCDs were the Type AC devices, which are only suitable for circuits with purely resistive loads (like heating). However, most renewable technologies, such as solar PV and battery storage systems, incorporate DC (direct current) components. This is where problems may arise. Type AC RCDs can struggle to detect faults in circuits that include DC current, as the RCD can become ‘blinded’ by the DC component. This can either prevent the RCD from tripping when needed
26 ELECTRICAL ENGINEERING • APRIL 2025
electricalengineeringmagazine.co.uk
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