MK Sentry RCD 100A 30MA 230V DP Type A 2 Module

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To help explain, it might be worth thinking about some older models of earth fault loop impedance testers, which could cause the RCD to operate unintentionally. To prevent this, some types of earth fault loop impedance testers imposed a DC current on the AC test current. This DC current saturated the magnetic core of the RCD preventing it from tripping under the test condition. This information should be held on record, with other design criteria and the Installation Test Certificate for the premises. This will be required in the event of claims for negligence (Public liability insurance). 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. Domestic properties with modern equipment and appliances, such as LED lighting, induction hobs, IT equipment and electric vehicle charging equipment.

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. Single-phase inverter designs, applied in washing machines and handheld appliances, containing variable speed features, may produce mixed frequency leakage currents. Appliances containing inverters and motors, can be used with Type A RCDs, if: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. 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 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". You might ask "Why are Type AC RCDs still referred to in the 18th Edition of BS7671, when most installations should be using Type A devices as a minimum requirement?" 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.

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. For single phase inverters used in motor speed control, the characteristics of the equipment will determine if Type A, F or B is required, to meet Regulation 531.3.3 For 3 phase inverters which do not incorporate isolating transformers, Type B RCDs must be used to meet the requirements of Regulation 531.3.3 For additional information. 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). I feel like BIG BUSINESS is trying to pull a fast one with the new 18th edition regs, they are trying to shift responsibility for their sometimes obvious poor standards onto the little man at the bottom of the food chain. It's pretty obvious that insurance companies are trying to get out of paying for damage caused by products that quite frankly should not be in peoples homes in the first place.Fault Protection. Any tripping current dependent on the resistance of the earth path. (Regulations 411.4.204; 411.5.1; 531.2). Type B devices are also suitable for Type AC, Type A and Type F applications. How do I test the different Types of RCD?

Some European countries have already banned the general use of Type AC RCDs and some manufacturers have stopped making them, supplying Type A in place of Type AC. High frequency current components can saturate the RCD, preventing detection of 50Hz residual currents.

Residual Current Circuit-Breaker (RCCB) without protection against overload BS EN 61008, BS 4293, BS EN 62423.

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 A RCDs are not designed to detect smooth dc residual currents. They will still trip within safe limits with < 6 mA smooth dc superimposed on a 50Hz pulsed residual current.

Type F RCD Risks:

In some other countries in Europe (perhaps not coincidentally the ones commonly using 3-phase supply to homes), it's much easier to find type-A or even type-B.