Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This Question of the Day, concerning circuit breakers & fuses - 4-pole RCDs and their correct functioning under certain circumstances, is answered by Eaton MEM Circuit Protection & Control:
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| A 4-pole RCD. |
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Question: We are often requested to install 3-phase pumps off a generator. Generally, the starter panel control circuits are fed off a transformer within the panel, and therefore there is no need for a neutral to be brought out to the panel. Will 4-pole RCDs function correctly if the only neutral to the RCD is from the generator? We have had instances where the test button doesn't operate on certain RCDs, but it's the overall picture we're interested in.
Answer: A 4-pole RCD will function correctly when connected into a 3-phase system without neutral. The residual current measurement and protection functionality does not rely on the presence of a neutral.
The test button function simulates an earth leakage internally through a resistor. Depending on manufacturer and product type, this resistor can be between a phase and neutral or between phase and phase. In the former case, the RCD trip test button will not work - as you have experienced - however the manufacturer can advise the appropriate resistor to be fitted externally between any phase and the unused neutral pole.
To see many more Q & A in Voltimum UK's Experts Area, please click on the link: http://www.voltimum.co.uk/consult.php?universe=consult.index.questions
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