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. Note: RCMs(Residual Current Monitors) are not suitablefor providing residual current protection and cannot be used in place of an RCD – see note in clause 411.1 RCDs are far more sensitive than circuit-breakers. The sensitivity being rated in milliamps (mA) as opposed to amps (A). Different Types of RCD

Commercial installations comprising LED lighting and large quantities of IT equipment which can also cause other issues, such as protective conductor current which should also be considered. 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). Residual Current Devices (RCDs) are safety switching devices. They are designed to provide safety for three types of protection; these are: Type A RCDs are used for alternating sinusoidal residual current and for residual pulsating direct current up to 6 mA. Residual Current Device is a generic term used for describing devices which incorporate residual current protection in accordance with one of the standards below:

What are RCDs?

All types of electrical installations could be affected, it depends on the equipment which has been installed. Examples include: NOTE 4: For guidance on the correct use of RCDs for household and similar use, see PD IEC/TR 62350. Earth Leakage Current (Protective Conductor Current): Electrical appliances, connections and cables allow some current to leak to earth, due to internal or natural capacitance associated with the installation. This current should travel to earth via the PE (protective earth) conductor. If the PE conductor is disconnected or faulty (high resistance), a person touching uninsulated parts of the equipment would be subject to the leakage current, that normally flows through the PE conductor. The regulations set limits for protective conductor currents and methods for connecting the protective conductor to the equipment – see 543.7 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 should be noted that the residual DC leakage current can vary with motor speed and cable length. In the UK, residual current protection has been installed with little consideration for the nature of appliances and loads connected downstream of the RCD, this can affect the operation of the 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.

Different Types of RCD

e) for residual smooth direct currents, whether suddenly applied or slowly increased, independent of 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. These are installed to protect circuits where equipment with electronic components are installed such as Swimming pool installations can be at risk when equipment such as pumps are being replaced with newer equipment incorporating VSDs, without any consideration as to whether the existing Type AC RCD is still suitable for the application.

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. Residual Current: A fault current that flows to earth, due to an insulation failure within an electrical installation i.e. the difference between the current flowing into and out of system via the live conductors.Temporary installations for structures, amusement devices and booths at fairgrounds, amusement parks and circuses, and 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? Domestic properties with modern equipment and appliances, such as LED lighting, induction hobs, IT equipment and electric vehicle charging equipment. If equipment contains Power Electronic Converter Systems (PECS), more commonly known as inverters or VSDs, BS 62477-1 Safety requirements for power electronic converter systems and equipment sets out the requirements and Annex H provides guidelines for RCD compatibility. Manufacturers must define the safety requirements clearly for suitable RCDs. If this information cannot be obtained, a Type B RCD should be installed to cover the worst-case scenario. Industrial installations using uninterruptible power supplies (UPS) and variable speed drive (VSD) frequency inverters for the speed control of motors.

NOTE 2: For RCD Type F, tripping is achieved for residual pulsating direct currents superimposed on a smooth direct 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. 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. NOTE 1: For RCD Type A, tripping is achieved for residual pulsating direct currents superimposed on a smooth directFault Protection. Any tripping current dependent on the resistance of the earth path. (Regulations 411.4.204; 411.5.1; 531.2). If the inspector is concerned that residual DC current may affect the operation of Type AC RCDs, the client must be informed. The client should be informed of the potential dangers which may arise and an assessment of the amount of residual DC fault current should be made to determine if the RCD is suitable for continued use. Depending on the amount of residual DC fault current, an RCD which is blinded by residual DC fault current is likely not to operate which could be as dangerous as not having an RCD installed in the first place. In-service reliability of RCDs RCD:Generic term for devices that can detect residual currents and are suitable for fault disconnection. Customers and even manufacturers use the term RCD, when they are talking about an RCCB or an RCBO. The 18th Edition Regs list the following RCD formats: RCCB:Residual current protection only. Must be used with MCB for overcurrent and short circuit protection. AKV, F, B and EV RCDs can withstand a fast transient <3kA/20µs. e.g. the Regulations recommend the use transient resistant RCDs, if the circuit contains surge protection devices (SPDs) on the load side of the RCD. ii) RCD Type A: RCD tripping on alternating sinusoidal residual current and on residual pulsating direct current, suddenly applied or smoothly increasing.