Food & Drink Process & Packaging Issue 11 2016 - Page 17

Designing or installing machines for connection to RCD protected sockets! Automated machines containing frequency inverters must not be connected to circuits protected by conventional RCDs (RCCB). Before installing the equipment, check the machine specification & inverter characteristics for specific requirements relating to RCD protection. RCCB Protection with Inverters To comply with Regulation 4(1) 65 Where the precautions taken include residual current protection to reduce the risk of death or injury (Regulation 8), the upstream RCD protection must be suitable for use with inverters nominal supply frequency (50Hz) which cannot be detected by and at various harmonic frequencies. conventional RCDs. In addition DC Leakage currents in the higher residual currents affect the tripping frequency ranges can be significant characteristics of AC RCDs, resulting and from a safety perspective cannot in a loss of protection due to magnetic be ignored, as can be seen from the saturation of the AC trip coil. connected downstream see Fig 2. following example. Electricity at Work Regulation 4(1) Figure 2 details the frequency range 65 The safety of a system depends of various leakage currents present upon the proper selection of all the in a system electrical equipment in the system containing a 4kW and the proper consideration of VSD; at 50Hz the the inter-relationship between the leakage current is individual items of equipment. less than 4mA. The The inverter design topology will determine the Type of RCD protection required. To meet existing laws on H&S, companies must comply with the inverter manufactures recommendations relating to the Type and characteristics of the RCD that can be used safely with the equipment. AC operational leakage currents: 3 Phase Inverters and the associated EMC filters and motor cables, generate leakage currents at Chaz Andrews – Technical Manager, Doepke UK Ltd maximum leakage current 60mA, occurs at 8 k Hz. This equipment can be matched to a Type B RCCB that meets UK 30mA protection at 50Hz and fire protection requirements Doepke above 150 Hz (see Reg 422.3.9 9 (i) < 300mA RCD sensitivity). We stock a comprehensive range of products for immediate despatch to DC Residual Currents: Under certain fault conditions 3 phase inverters produce smooth DC residual currents customers throughout the United Kingdom. FDPP - 17