Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning earth loop test results, circuit breakers and discrimination, is answered by ABB:
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Question: On a periodic test, it was found that the earth loop at the end of the final circuits was a lot higher than allowed by the maximum earth loop of the MCCB at the start of the installation. The installation is only five years old.
The NICEIC's view on this is that the installation certificate should therefore be 'unsatisfactory'. How can we advise the client on a solution for this?
Answer: My understanding is that it is the maximum Zs of the final load protection device that should be the value used for the protection of the final load circuit, rather than that of the device at the start of the installation.
In order to have discrimination in the system, the final load protection device should be the one to operate in the event of an earth fault in the final circuit, rather than the device at the start of the installation.
You should still confirm this with the NICEIC - it may be the organisation misunderstood your question. If this is still a problem and your final load device does not offer sufficient protection to your end load, you would need to fit an RCD. This was the requirement for the 16th Edition, as it is now for the current 17th Edition.
To see many more Q & A in Voltimum UK's Experts Area, please click on the link: www.voltimum.co.uk/consult.php?universe=consult.index.questions
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