Published: 28 August 2014
Category: Q&A
James asks this question, which is about discrimination and the best way to achieve it. It has been answered by the NICEIC (Theme – Distribution Equipment including Cable Management):
This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.
Question: In the case of a consumer unit DP disconnector fitted with 100mA RCCB protection and final circuits fitted with 30mA RCBO protection, should the disconnector be a time delayed S-Type?
Or should I even remove the 100mA facility and use it only as an isolator?
Or is the original combination acceptable to achieve electrical discrimination?
Answer: To answer your first question, if the main switch is a time delayed RCD, this will offer better discrimination than a non-delayed 100mA RCD.
The second part to your question depends? upon whether the main switch is required as an RCD, say in a TT system. If the DB in question has appropriate RCD protection for circuits in the form of (say) RCBOs, and they do not affect any downstream circuits with further RCD protection, then it may not be required (nor desirable) to have the main switch also as an RCD.
It is very dependent upon the setup you have, and there are many different combinations possible to achieve a good electrical design.
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