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Student & Learning Zone - City & Guilds
What fault can turn a TT into a TNCS and disable the RCD?
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<blockquote data-quote="NozSpark" data-source="post: 263306" data-attributes="member: 601"><p>Well if it's open to anyone here's the answer</p><p></p><p>Treat it as a potential divider,,, say 0.2ohms to neutral and 200ohms to earth with a (N-E) fault of say 1kohms, this will give us a fault resistance of 1000.2ohms - 1000 + ((200x0.2)/(200+0.2)) and a fault current of 230mA.</p><p></p><p>Any fault current down the earth will travel down the earths until it reaches the N-E fault, at which point 99% of the fault current will go down the Neutral and only 1% down the Earth, so that will give 227mA down the Neutral and 3mA down the earth..... Therefore not enough L-N imbalance to trip the RCD</p></blockquote><p></p>
[QUOTE="NozSpark, post: 263306, member: 601"] Well if it's open to anyone here's the answer Treat it as a potential divider,,, say 0.2ohms to neutral and 200ohms to earth with a (N-E) fault of say 1kohms, this will give us a fault resistance of 1000.2ohms - 1000 + ((200x0.2)/(200+0.2)) and a fault current of 230mA. Any fault current down the earth will travel down the earths until it reaches the N-E fault, at which point 99% of the fault current will go down the Neutral and only 1% down the Earth, so that will give 227mA down the Neutral and 3mA down the earth..... Therefore not enough L-N imbalance to trip the RCD [/QUOTE]
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Student & Learning Zone - City & Guilds
What fault can turn a TT into a TNCS and disable the RCD?
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