NOTE 4: For guidance on the correct use of RCDs for household and similar use, see PD IEC/TR 62350. The DC link values of capacitance and voltage, do not result in smooth dc values < 6 mA, being imposed on the AC pulsed wave form. The RCD type should not be confused with the different types of circuit-breakers which are manufactured according to their time/current characteristics. Circuit-breakers for overcurrent protection of cables are available in types B, C and D in accordance with BSEN 60898-1. It's quite easy to see how an RCBO with a B Type time-current curve could be mistaken for a Type B RCD.

RCD failing to trip when the appliance is running, and the RCD test button is operated, could be an indication that the appliance is affecting the RCD. Type B devices are also suitable for Type AC, Type A and Type F applications. How do I test the different Types of RCD? 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. Type A RCDs are used for alternating sinusoidal residual current and for residual pulsating direct current up to 6 mA. There are many different RCD types available, each being suitable for different equipment types, as identified in Regulation 531.3.3 of BS 7671:2018.

Type F RCDs are not designed to detect smooth dc residual currents. They will still trip within safe limits with < 10 mA smooth dc superimposed on a 50Hz pulsed residual current.

The method of installation relating to protective earthing will depend on the operational leakage current (protective conductor current) – see 543.7. The use of a 30mA RCD may be required for several reasons; cable installation, location / application area for the pump etc. Take note of 531.3.2 Operational leakage current (protective conductor current) for the circuit should not exceed 30% of the RCD sensitivity.

Justifying the use of Type F RCDs

Where electric vehicle charging equipment is likely to create a residual DC fault current, manufacturers may provide the correct type of RCD within the charging equipment. However, problems could arise if the charging equipment is installed downstream of an existing Type AC RCD, which could be blinded by the residual DC fault current. In some types of DC charging equipment, the AC input side is galvanically isolated from the DC output which, hence, provides electrical separation. This means that faults on the DC output side, connected to the vehicle, would not be detected by an RCD on the input side of the circuit. What are the hazards and problems? The revised RCD guidance in 531.3.3 is precise. The appropriate Type of RCD must be selected, based on the characteristics of the residual current and the equipment that is likely to be connected to the RCD protected circuit". In a healthy circuit, the vector sum of the currents flowing in all live conductors should be nominally zero. When a fault occurs on a circuit causing a current to flow to earth, this creates an imbalance and trips the device. What is DC residual/fault current? Some equipment will have DC leakage current by the nature of design, other equipment may produce DC currents during fault conditions, dictated by the construction of the equipment.

i.e. WWFC 1877 Mr Wolves Football supporter I guess - This article raises several questions commonly posed by Installers (see the question marks). The DC link values of capacitance and voltage, do not result in smooth dc values < 10 mA, being imposed on the AC pulsed wave form. Temporary installations for structures, amusement devices and booths at fairgrounds, amusement parks and circuses, and Type AC RCDs (General Type), which are most commonly installed in dwellings, are designed to be used for alternating sinusoidal residual current to protect equipment which is resistive, capacitive or inductive and without any electronic components.ii) RCD Type A: RCD tripping on alternating sinusoidal residual current and on residual pulsating direct current, suddenly applied or smoothly increasing. There's never going to be a perfect solution but there does need to be a less complex solution than there is. Assuming an AC Type RCD will suit every installation is incorrect and RCDs shall be selected according to the equipment which is likely to be used within the installation. Type AC RCDs shall only be selected where it can be assured that there is not and will not be any residual DC fault current on the circuit. The fault current (If) contains mixed frequency components between 10Hz (minimum motor frequency) and 1kHz (maximum inverter switching frequency) ***. NOTE 2: For RCD Type F, tripping is achieved for residual pulsating direct currents superimposed on a smooth direct

Requirement for a transient resistance feature < 3 kA and short 10 ms time delay. **Note: Type A transient resistant RCDs only meet EN 61008/9 for general UK 50Hz residual currents. Different types of RCD exist, depending on their behaviour in the presence of DC components and frequencies. The appropriate RCD shall be selected from the following: So - please help me - have I lost touch with the right places to buy RCDs in the UK? Where can one get a fairly broad selection of different types (A, B) at reasonable price? Why do I find almost entirely AC?

The initial verification required under 641.1 and 301.1 (ii), covers the requirements for the verification that electrical equipment (any appliance supplied or connected, as part of the existing fixtures and fittings) is compatible with other electrical equipment such as RCDs installed to provide additional protection e.g. for a domestic installation, document the appliance RCD requirements with the justification for the consumer unit specification. Type AC RCDs subjected to pulsed waveforms will not trip within the safe limits, required for 30mA protection. Appliances containing diodes, produce pulsed residual currents – see Fig 1. Diodes became so common in domestic equipment some years ago, that many countries banned the "general use" of Type AC RCDs e.g. From 1985, VOE Regulations specified the use of Type A RCDs in all domestic installations as a minimum requirement.