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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="kme" data-source="post: 263335" data-attributes="member: 113"><p>Nozzer is spot on mate - it is worth being aware that a N-E short somewhere upstream can render an RCD inoperative as a safety device, yet not cause it to trip.</p><p></p><p>One of the (myriad) reasons for doing RCD tests with NO loads connected - just switching off the MCBs doesn`t cut the mustard.</p><p></p><p>Had this about 10 yrs ago - I replaced THREE F`in RCD, cos they HAD to be faulty - wouldn`t trip on 1x or 5x, or even test button - all MCBs off.</p><p></p><p>Finally did individuated circuit IRs, and found a N-E "compression connection" ( someone fitting a faceplate had the neutral <em>just</em> outside the edges of the pattress; and tightening the front had crushed it against the metalwork. RCD never tripped.</p><p></p><p>I believe the newer "electronic" ones do not suffer the same problem ( it used to be a well known failing), but it <em>can</em> still occur.</p><p></p><p>KME</p></blockquote><p></p>
[QUOTE="kme, post: 263335, member: 113"] Nozzer is spot on mate - it is worth being aware that a N-E short somewhere upstream can render an RCD inoperative as a safety device, yet not cause it to trip. One of the (myriad) reasons for doing RCD tests with NO loads connected - just switching off the MCBs doesn`t cut the mustard. Had this about 10 yrs ago - I replaced THREE F`in RCD, cos they HAD to be faulty - wouldn`t trip on 1x or 5x, or even test button - all MCBs off. Finally did individuated circuit IRs, and found a N-E "compression connection" ( someone fitting a faceplate had the neutral [I]just[/I] outside the edges of the pattress; and tightening the front had crushed it against the metalwork. RCD never tripped. I believe the newer "electronic" ones do not suffer the same problem ( it used to be a well known failing), but it [I]can[/I] still occur. KME [/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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