Solar photovoltaic systems incorporate inverters to convert DC to AC for use either within the electrical installation or to be supplied to the National Grid. Some inverters may provide galvanic or electrical separation between the AC mains supply and the DC side of the PV array. Where this is not the case, some manufacturer’s instructions state that Type B RCDs to BS EN 62423 must be used. Earth Leakage Current (Protective Conductor Current): Electrical appliances, connections and cables allow some current to leak to earth, due to internal or natural capacitance associated with the installation. This current should travel to earth via the PE (protective earth) conductor. If the PE conductor is disconnected or faulty (high resistance), a person touching uninsulated parts of the equipment would be subject to the leakage current, that normally flows through the PE conductor. The regulations set limits for protective conductor currents and methods for connecting the protective conductor to the equipment – see 543.7 In the UK, residual current protection has been installed with little consideration for the nature of appliances and loads connected downstream of the RCD, this can affect the operation of the RCD.

Appliances used in domestic, agricultural and commercial premises, including certain types of washing machine, induction hobs, LED lighting, pumps etc. can produce residual currents that are not compatible with type AC RCDs. The general safety guidance given in the 17th Edition for RCDs, is no longer appropriate for many appliances and loads connected in these installations. Consequently the 18th Edition Wiring Regulations have been updated to align with the existing Electrical Safety Standards already adopted in other countries.Modern appliances are becoming increasingly more sophisticated, featuring microprocessor technology with an emphasis on energy reduction. This has led manufacturers to incorporate energy-saving measures, such as speed control, which by the nature of its operation has an element of DC residual fault current. Which types of installation could be affected? An RCD monitors the earth leakage current in a circuit. It is constructed from coils of wire wound around a ferrite toroid core, one for each live conductor of the circuit protected. When a current imbalance between live conductors is detected, a voltage will be induced in the tripping coil which will disconnect the electrical supply to the protected circuit (see Figure 1). In the 18 th Edition, the term for discrimination has been changed to selectivity. It is important to achieve selectivity when installing multiple RCDs in series. A common misconception is that an RCD with a higher mA sensitivity rating will provide selectivity, but this is not the case due to the instantaneous operation of the device. The only way to achieve selectivity with RCDs is to install a time-delayed device upstream. NOTE 2: For RCD Type F, tripping is achieved for residual pulsating direct currents superimposed on a smooth direct Temporary installations for structures, amusement devices and booths at fairgrounds, amusement parks and circuses, and

Residual Current Circuit-Breaker (RCCB) without protection against overload BS EN 61008, BS 4293, BS EN 62423.e) for residual smooth direct currents, whether suddenly applied or slowly increased, independent of Residual Current Device is a generic term used for describing devices which incorporate residual current protection in accordance with one of the standards below: NOTE 5: Some typical fault currents in circuits comprising semiconductors are given in Annex A53, Figure A53.1.” What are the effects of DC residual fault current on RCDs?