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Max Zs For A Rcd
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<blockquote data-quote="Rob_the_rich" data-source="post: 381531" data-attributes="member: 8419"><p>It does seem odd at first sight that the figures given for overcurrent protection use Zs which uses the path of an earth fault. It seems to assume that the pefc conditions would be more onerous than pscc, which would be the case for t+e cable with a reduced cpc csa.</p><p></p><p>AIUI, with RCBOs the mechanism for overcurrent and the mechanism for earth fault current are separate, even though an overcurrent may occur due to an earth fault. Table 41.3 is used therefore to ensure that the overcurrent mechanism will work regardless of the type of overcurrent. If the overcurrent turns out to be an earth fault current, then the RCD mechanism would trip sooner.</p><p></p><p>Incidentally, I found an eaton rcbo with voltage independence here <a href="http://www.eaton.uk.com/EatonUK/ProductsSolutions/Electrical/ProductsServices/CircuitProtection/ResidualCurrentCircuitBreakerwithintegratedOvercurrentProtection/CombinedRCDMCBforBritishStandard/index.htm" target="_blank">http://www.eaton.uk.com/EatonUK/ProductsSolutions/Electrical/ProductsServices/CircuitProtection/ResidualCurrentCircuitBreakerwithintegratedOvercurrentProtection/CombinedRCDMCBforBritishStandard/index.htm</a></p><p></p><p>Still trying to get my head around VD and VI RCDs, and the TNCS scenario posted.</p></blockquote><p></p>
[QUOTE="Rob_the_rich, post: 381531, member: 8419"] It does seem odd at first sight that the figures given for overcurrent protection use Zs[I] [/I]which uses the path of an earth fault. It seems to assume that the pefc conditions would be more onerous than pscc, which would be the case for t+e cable with a reduced cpc csa. AIUI, with RCBOs the mechanism for overcurrent and the mechanism for earth fault current are separate, even though an overcurrent may occur due to an earth fault. Table 41.3 is used therefore to ensure that the overcurrent mechanism will work regardless of the type of overcurrent. If the overcurrent turns out to be an earth fault current, then the RCD mechanism would trip sooner. Incidentally, I found an eaton rcbo with voltage independence here [URL="http://www.eaton.uk.com/EatonUK/ProductsSolutions/Electrical/ProductsServices/CircuitProtection/ResidualCurrentCircuitBreakerwithintegratedOvercurrentProtection/CombinedRCDMCBforBritishStandard/index.htm"]http://www.eaton.uk.com/EatonUK/ProductsSolutions/Electrical/ProductsServices/CircuitProtection/ResidualCurrentCircuitBreakerwithintegratedOvercurrentProtection/CombinedRCDMCBforBritishStandard/index.htm[/URL] Still trying to get my head around VD and VI RCDs, and the TNCS scenario posted. [/QUOTE]
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