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Maximum Zs
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<blockquote data-quote="Doc Hudson" data-source="post: 456280" data-attributes="member: 1607"><p>Do you understand the concept of what the maximum earth fault loop impedance is for, or have you read the section 411.4.xx in BS7671. If you are using MCB's to achieve the disconnection times, to comply with 411.3.2.2. in the event of a fault of negligible impedance between Line and earth, then you must not exceed the maximum Zs values. If you go back and re-read the appropriate sections you will answer your own question. It sounds as though you are getting confused with TT systems where additional protection is required because of the high external earth loop impedances due to the lack of a direct physical earth path back to the supply transformer. </p><p></p><p>Doc H.</p></blockquote><p></p>
[QUOTE="Doc Hudson, post: 456280, member: 1607"] Do you understand the concept of what the maximum earth fault loop impedance is for, or have you read the section 411.4.xx in BS7671. If you are using MCB's to achieve the disconnection times, to comply with 411.3.2.2. in the event of a fault of negligible impedance between Line and earth, then you must not exceed the maximum Zs values. If you go back and re-read the appropriate sections you will answer your own question. It sounds as though you are getting confused with TT systems where additional protection is required because of the high external earth loop impedances due to the lack of a direct physical earth path back to the supply transformer. Doc H. [/QUOTE]
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