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Detecting DC residual and leakage currents

Making the energy transition work means safely integrating new technologies into buildings to do things like charge electric vehicles, generate renewable power and store energy. To keep people and assets safe from the residual currents that these technologies can create, installing new-generation protective switchgear is vital. 

Why do you need to detect >6 mA DC leakage current?

Upgrading buildings to respond to energy transition will be a mission-critical task for many businesses in the months ahead. But before you plunge into the detail, you must understand three vitally important safety rules: 

1

Be aware that some new technology including photovoltaic inverters, EV chargers and battery storage systems can generate smooth DC fault currents. 

2

Know that DC fault currents can 'blind' traditional RCDs which can lead to danger to people and property.

3

Be ready to integrate new technologies safely by taking the right protective measures. 

Down in the detail of DC leakage current

When using technology such as PV inverters, EV charging systems or battery storage systems, residual currents can comprise either pure or pulsating direct current. Residual currents carry a safety risk and can lead to danger to people and property. 
Conventional switchgears, which are designed for AC currents, cannot detect DC residual currents or are negatively affected by them, so devices that may be affected must be provided with all-current sensitive protection. Some applications demand protection at the highest levels of sensitivity and accuracy because their power electronics can cause leakage current through line filters and, above a certain level, this impairs the ability of a standard ‘Type A’ residual current circuit breaker to trip, effectively causing the switchgear to go blind. 

Clearly, this is very dangerous, so Type B residual current devices are best suited when more than 6 mA DC leakage current flows in the installation.  

It is important to be aware that EV charging is one of the most well-known causes of switchgear ‘blinding’ and you must implement the necessary protective precautions. 

Learn more about Type B circuit breakers for EV chargers

Safe, reliable EV charging is linked directly to electrical safety in building installations. The relevant standard (IEC 61851-1) says that charging stations must be provided with earth leakage protection that can detect DC direct current. In practice, this can be done with a ‘Type B’ leakage circuit breaker.

'Type B' residual circuit breaker meets the highest safety standards when used for fault protection and achieves the highest accuracy through digital detection, preventing unwanted false tripping and ensuring maximum system availability. It is the level of protection needed to integrate new technologies safely.

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