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

Product Information

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.

i) RCD Type AC: RCD tripping on alternating sinusoidal residual current, suddenly applied or smoothly 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. Residual Current Device is a generic term used for describing devices which incorporate residual current protection in accordance with one of the standards below: Industrial installations using uninterruptible power supplies (UPS) and variable speed drive (VSD) frequency inverters for the speed control of motors.Circuit feeding a single-phase micro-wave oven with inverter-controlled output to the magnetron. A fault on the output side of the bridge rectifier will produce a pulsed fault current (If fig 1), generated at the supply frequency. For applications using single phase inverters for speed control (washing machines, GSHPs etc ), the design characteristics of a single-phase inverter will determine if it is safe to use Type A RCDs upstream. 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?

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. 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.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. 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:

In existing electrical installations, Type AC RCDs have been installed for many years and are effective for equipment which is resistive, capacitive or inductive and fitted with minimal electronic components. This used to be the case for most installations when lighting was of the tungsten type, and the electrical appliances or equipment did not contain any electronic equipment. NOTE 3: For RCD Type B, tripping is achieved for residual pulsating direct currents superimposed on a smooth direct current up to 0.4 times the rated residual current (IΔn) or 10 mA, whichever is the highest value. 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. UK electricians can still make informed technical decisions. This is explained in Chapter 12, 13 and Chapter 30. The Electrician is responsible, not the Technical committee, to make the decision on which device is appropriate for the installation. 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. and the RCD should be selected based on the characteristics of the connected loads.The advent of new technologies has created different challenges for the electrical designer and installer. Some modern equipment can create DC residual fault current. Such items include, variable-speed drives, LED lighting, washing machines, dishwashers and tumble dryers. It is important to understand that RCDs cannot limit voltage or current, they provide protection by limiting the time a specific maximum current can flow to earth. RCDs work by monitoring the flow of current in a circuit's live conductors and, if the flow of current is imbalanced due to an earth leakage current of a set nominal value, the device will trip to cut off the supply to the circuit. Whilst RCDs have a nominal tripping current (IΔn), they may trip below the nominal value; for instance, a 30 mA RCD is required to trip at a current between 18 mA to 28 mA. The method of installation requires 30mA RCD protection – e.g. Regulation 415.1 & 522.6.202. Dedicated circuit feeding an immersion heater, conventional oven or cooker, with resistance heating elements.