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

Product Information

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 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. A Type S RCD is a sinusoidal residual current device incorporating a time delay. It can be installed upstream from a Type AC RCD to provide selectivity. A time-delayed RCD cannot be used for additional protection because it will not operate within the required time of 40 mS. 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.

I believe the article makes it clear that the their are 4 Types of RCD that may need to be considered - Quote from the article - The primary principle of an RCD is to protect the persons using the installation, if manufactures are going to be allowed to make equipment that is going to end up in peoples homes then British Standards must make it compulsory for manufactures to state in bold writing how that equipment will affect an installation where RCD's are present, it's already common practice for many manufactures to state what the maximum protective device is to be used with their equipment, so make it their responsibility. 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. High frequency current components can saturate the RCD, preventing detection of 50Hz residual currents. 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 fault current (If) contains mixed frequency components between 10Hz (minimum motor frequency) and 1kHz (maximum inverter switching frequency) ***. 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. i) RCD Type AC: RCD tripping on alternating sinusoidal residual current, suddenly applied or smoothly

These are installed to protect circuits where equipment with electronic components are installed such as 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. 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?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.