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21 ohm excluding consumer's earth electrode.
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<blockquote data-quote="Robojin" data-source="post: 38110" data-attributes="member: 2209"><p>How it was explained to me, 21Ω is used in the calculation on the rating selection of an RCD used to meet you disconnection times</p><p></p><p>As the others have stated 21Ω is what the DNO supplies at the substation to earth for TT systems</p><p></p><p>So for you, your Ze = 21Ω, using the regs you are permitted a max 200Ω Zs, if for argument you had an R1+R2 on a circuit of 10Ω (just a number) you add 21+200+10=231 divide this by 50 touch voltage, so 231/50=0.22A convert to 220mA, your RCD must not exceed 220mA or you will not meet disconnection times, so for practical reasons that would be 100mA protecting the instalation</p><p></p><p>Of course the above assumes you have and earth electrode or equivalent in place <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite8" alt=":D" title="Big grin :D" loading="lazy" data-shortname=":D" /> </p><p></p><p>Hope that helps, if I missed something Andy let me down gently <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite3" alt=":(" title="Frown :(" loading="lazy" data-shortname=":(" /></p></blockquote><p></p>
[QUOTE="Robojin, post: 38110, member: 2209"] How it was explained to me, 21Ω is used in the calculation on the rating selection of an RCD used to meet you disconnection times As the others have stated 21Ω is what the DNO supplies at the substation to earth for TT systems So for you, your Ze = 21Ω, using the regs you are permitted a max 200Ω Zs, if for argument you had an R1+R2 on a circuit of 10Ω (just a number) you add 21+200+10=231 divide this by 50 touch voltage, so 231/50=0.22A convert to 220mA, your RCD must not exceed 220mA or you will not meet disconnection times, so for practical reasons that would be 100mA protecting the instalation Of course the above assumes you have and earth electrode or equivalent in place :D Hope that helps, if I missed something Andy let me down gently :( [/QUOTE]
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21 ohm excluding consumer's earth electrode.
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