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• • •   • • •   Heat Pumps – Type F or Type B RCDs?


fault current is > 10 mA, BS7671 requires the use of Type B – see 531.3.3 Note 3. For the benefit of Equipment Manufactures,


BS7671 Table A53 lists some basic configurations for different inverter topologies (Power Electronic Control System - PECS) and the associated Types of RCD. Manufacturers of self-contained equipment are responsible for testing and providing information on the operational AC leakage current (current flowing in the PE conductor). For standalone inverter drives, use motors, filters and inverters from a reputable company, who provided recommendations on RCD Type and sensitivity requirements.


RCD SENSITIVITY I


nverter speed controlled pumps and compressors circuits require specific Types of RCD. The characteristics of the inverter used to


control the speed, will determine if you require Type F or Type B RCDs and any associated restrictions on RCD sensitivity. Check with the Manufacturer of the standalone heat pump equipment before quoting for the installation.


BS7671 Regulation 531.3.3 details the


requirements for selecting the correct Types of RCD, based on the characteristics of the leakage current frequency and dc fault current components produced by the equipment.





Note: Type F or B RCDs must not be installed downstream of existing Type AC or A RCDs.


EQUIPMENT DESIGN CHARAC- TERISTICS AND INSTALLATION DESIGN


The selection of Type F or Type B RCDs is governed by the inverter topology and the value of the dc link voltage, which in turn determines the level of smooth dc residual current produced under certain fault conditions. Type F can be used < 10 mA smooth dc - see 531.3.3 Note 2. If the smooth dc 


 


The ac operational leakage current (PE current), must be compatible with the installation design and the RCD sensitivity requirements. Consider the possible addition of leakage currents, when adding new equipment to an existing installation, as this may require sub-division of existing circuits - see 531.3.2 (i). The total operational leakage current should not exceed 30% of the associated RCD sen- sitivity. This allows a safety margin for the effect of accepted levels of harmonics and normal supply voltage tolerances.


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  49  


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