Published: 9 April 2015
Category: Q&A
Jim asks this question about a variable speed drive (VSD), its power supply, and whether an RCD should be installed to provide protection without nuisance tripping. It has been answered by ABB (Theme – Power):
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Question: Is it possible to install a 3ph RCD between a VSD and a socket outlet supplying a motor to provide RCD protection?
Would you get nuisance tripping or lack of functionality because of the waveform of the drive’s output?
Answer: VSDs can cause nuisance tripping depending upon the level of harmonics they send to earth, and this depends on the design adopted by the VSD manufacturer concerned.
ABB offers a complete range of electronic residual current devices, in accordance with IEC 6094-2, Annex M. The combination of RD3 and RCQ020 range with miniature circuit breakers of the S200 family and Tmax MCCBs ensures residual current protection up to 1250A.
As this case seems critical, my suggestion is to propose an RD3M device, which includes a frequency filter designed to cut the harmonics disturbances.
Because of the 947-2 Annex M setting the device at 30mA, you will also have people protection.
Please see the catalogue as a PDF attached below (2MB file size).
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