Quality, health and safety experts, Bureau Veritas, have warned that an increasing number of AC-type residual current devices (RCDs) are being affected by direct currents (DC) from modern electronic devices, electric appliances, and renewable energy sources. 
 
The previous (17th Edition) Wiring regulations said that AC-type RCDs should be used for sockets that might supply outdoor equipment. However, with increasing number of domestic, commercial and industrial sites now installing renewable energy sources such as solar panels, Bureau Veritas says that these RCDs might not be fit for purpose. 
Modern technology changes waveforms 
Modern electrical installations include technology and products that change the shape of electrical waveforms. These include photovoltaic (PV) panels and electric vehicle chargers, which can leak direct current back into the electrical system, saturating the iron core of the AC-type RCDs, which aren’t designed to handle it. 
 
DC leakage can also be created by faulty equipment, and even faulty mobile phone chargers or USB sockets. 
 
The recommendation 
Bureau Veritas suggests A- or B-type RCDs that are specifically designed to offer protection against alternating and pulsating direct currents should be used. However, although this is included in the new (18th Edition) Wiring Regulations, Bureau Veritas says it doesn’t do far enough. 
 
For general purposes, AC-type RCDs are still recommended, and A-type RCDs are more expensive and aren’t yet widely available. Bureau Veritas says that regulations will need to be changed in the future. 
 
The challenge 
Specifying the correct RCDs is complicated so the best solution is to make sure that you carry out regular inspection and testing to be sure your installation is safe and compliant, especially if it is connected to renewable energy sources or electric vehicle charging points. 
RCD types 
Function 
AC-type RCD 
Detecting residual alternating currents (AC) for general use. 
A-type RCD 
As well as detecting AC currents, A-type RCDs detect pulsating DC residual current. They are designed for single phase class 1 electronic loads. 
B-type RCD 
B-type RCDs can detect AC, pulsating DC, composite multi-frequency and smooth DC residual currents. Tripping conditions can be set for different frequencies from 50Hz to 1kHz. 
 
B-type RCDs are intended for loads with three-phase rectifiers, such as variable speed drives, photovoltaic (PV) systems, electric vehicle (EV) charging points and medical equipment. 
F-type RCD 
F-type RCDs have been introduced recently and are specially designed for circuit protection where single-phase variable speed drivers could be used. For example, energy-efficient washing machines and air conditioning systems use variable motor frequency, convertor switching frequency and line frequency, which can create composite or multi-frequency circuits. 
If you would like to check that your RCDs are doing their jobs properly, just give us a call
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