In this LearnElectrics video we look at how to find a Zs value or Earth Fault Loop Impedance, when the fuse size that you need, for the disconnection time that you need, is not shown in the Regulations book. And in this video, we will make reference to Amendment 2 of the Wiring Regulations, the brown book.
A question that is often asked on social media states that the fuse size for which a Zs is needed, is not listed. How can I find the Zs for my test results?
And a question that was sent to me by email ..
I have a BS88-3 system C fuse at 80 amps and I need a Zs value for 0.4 seconds disconnection time.
The fuse size is not shown in table 41.2 of the Regulations book, what can I do?
The video begins by looking at this last question and then works through several other examples, showing you the method and the calculations to arrive at the correct answer.
Also, the LearnElectrics video shown on the following link will give further information about tabulated and measured Zs values, and that all important 80% rule.
THE 80% RULE - Zs MEASURED - Zs TABULATED - WHAT IS THE DIFFERENCE? - WHICH ONE TO USE WHEN AND WHY
• THE 80% RULE - Zs MEAS...
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6 окт 2024
