Q & A of the Day – Does this RCD protection counteract the high resistance value?

Published: 12 March 2012 Category: Q&A

Kyle Denver asks about clarification on maximum Zs values concerning a ring final circuit supplied by an RCBO. His question is answered by the NICEIC (Theme – Regulations & Legislation):

Q & A of the Day – Does this RCD protection counteract the high resistance value?

This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.

Question: I'm just looking some clarification on maximum Zs values.

In the following example, a ring final circuit is supplied by a c32 RCBO 61009. The Zs value of the circuit is 2ohms. However the maximum Zs value of the protective device is 0.72 at 100%. Does the RCD protection counteract the high resistance value, thus leaving this circuit compliant?

This seems to be a grey area, and any relevant information would be very useful…

Answer: Follow Regulation 411.4.9, where a 61009 RCBO is used to meet the disconnection time requirements of 411.

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