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Student & Learning Zone - City & Guilds
2392 theory exam: maximum earth loop impedance
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<blockquote data-quote="louisIV" data-source="post: 178360" data-attributes="member: 5162"><p>I mis-copied the original question. It gave the value of the breaker (32A). Sorry for that. I can't really memorise all the maximum Zs values for all the breakers and fuses, which is why I was wondering about calculation.</p><p></p><p>Spinlondon - thank you. I'm not sure why I work with 5.5 rather than 55, but your formula allowed me to get to the correct answer in the paper.</p><p></p><p>Doesn't seem to work for another similar question in another paper which simply says,</p><p></p><p><strong>The maximum earth loop impedance to BS 7671:2008 for a circuit protected by a 20A BS88 fuse giving a 5 second disconnection time is:</strong></p><p></p><p><strong>a) 7.42ohms</strong></p><p></p><p><strong>B) 2.91ohms</strong></p><p></p><p><strong>c) 1.84ohms</strong></p><p></p><p><strong>d) 1.35ohms</strong></p><p></p><p>This one doesn't even give a nominal voltage. Am I expected to just know all the values on tables 41.3 to 41.4?</p><p></p><p><span style="font-size: 8px"><span style="color: #C0C0C0">---------- AUTO MERGE Post added at 14:18 ---------- Previous post was at 14:11 ----------</span></span></p><p></p><p>... And also know Table 41.6 (which covers 55V) off by heart?</p></blockquote><p></p>
[QUOTE="louisIV, post: 178360, member: 5162"] I mis-copied the original question. It gave the value of the breaker (32A). Sorry for that. I can't really memorise all the maximum Zs values for all the breakers and fuses, which is why I was wondering about calculation. Spinlondon - thank you. I'm not sure why I work with 5.5 rather than 55, but your formula allowed me to get to the correct answer in the paper. Doesn't seem to work for another similar question in another paper which simply says, [B]The maximum earth loop impedance to BS 7671:2008 for a circuit protected by a 20A BS88 fuse giving a 5 second disconnection time is:[/B] [B]a) 7.42ohms[/B] [B]B) 2.91ohms[/B] [B]c) 1.84ohms[/B] [B]d) 1.35ohms[/B] This one doesn't even give a nominal voltage. Am I expected to just know all the values on tables 41.3 to 41.4? [SIZE=8px][COLOR=#C0C0C0]---------- AUTO MERGE Post added at 14:18 ---------- Previous post was at 14:11 ----------[/COLOR][/SIZE] ... And also know Table 41.6 (which covers 55V) off by heart? [/QUOTE]
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2392 theory exam: maximum earth loop impedance
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