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: 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). 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. 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. Residual Current Devices (RCDs) are safety switching devices. They are designed to provide safety for three types of protection; these are: 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.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). 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. 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. 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? 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.

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 i.e. WWFC 1877 Mr Wolves Football supporter I guess - This article raises several questions commonly posed by Installers (see the question marks). In new installations, it is common practice to install a consumer unit which was supplied with RCDs already connected. These are likely to be Type AC which could be ineffective due to the residual DC fault current created by types of electrical equipment. Many installers, either because of habit or a misunderstanding of the limitations for an AC Type RCD, often assume they are suitable for all installations, but this is incorrect. 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 term general purpose relating to Type AC devices should not be taken out of context i.e. it is the most basic RCD, suitable for detecting a simple full sine wave residual current at 50Hz.RCDs are far more sensitive than circuit-breakers. The sensitivity being rated in milliamps (mA) as opposed to amps (A). Different Types of RCD

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. 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. I agree with you on that one, as electricians we have very little control over what will eventually be connected to an installation that we have installed. NOTE 4: For guidance on the correct use of RCDs for household and similar use, see PD IEC/TR 62350. What I would say is look at the article as a whole, as it makes it quite clear that 531.3.3 refers to 4 Types of RCD, and the points to consider when selecting RCDs for circuits containing various items of equipment. It also makes the point about consulting the manufacturer of the equipment for advice.

Type A RCD Risks

Type F RCDs cannot provide protection in circuits where there is a requirement to detect smooth DC residual currents, or if the motor frequency can be reduced to zero or the inverter switching frequency is >1kHz. If any of the above conditions apply, Type B RCDs must be used. 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. 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.