Published: 4 July 2014
Category: Q&A
Ray asks this question which concerns a variable speed drive (VSD), its power supply, and whether an RCD can be installed to provide protection without nuisance tripping. It has been answered by ABB (Themes – Electrical Control):
This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.
Question: Is it possible to install a three-phase RCD between a VSD and a socket outlet supplying a motor to provide RCD protection?
Could this result in nuisance tripping, or a lack of functionality because of the waveform of the drives output?
Answer: VSDs can cause nuisance tripping, depending on the level of harmonics they send to earth and this depends on the products from the VSD manufacturer concerned.
As this case seems critical, my suggestion is to propose an RD3M device, which includes a frequency filter designed to cut the harmonics disturbances.
The RD3 series of electronic residual current relays provides residual current protection and monitoring functions.
Note that, thanks to the 947-2 Annex M setting the device at 30mA, you will also have people protection.
Please see the attached PDF document for product information (2MB file size).
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