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Discuss zs readings before and after rcd. in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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anyone come across this before zs at board 0.28. then when measure zs on rcd side on live and neutral, reading of 0.77. from the same earth position.?, ie got a socket a meter away from board earth loop 0.81. measure earth from socket to board its 0.02.
 
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telectrix

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RCD affecting reading.
 

telectrix

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that's nothing. i once has a RCD adding 149 ohms to the Zs. took me almost an hour to suss it out,
 

telectrix

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Isn't this called RCD uplift? Where the RCD is affecting the reading
and so the thread degenerates into ladies' underwear.;);)
 

Taylortwocities

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I think that the "no trip" feature of the test meter sways the Zs readings.. my Metrel is about half an ohm different.
 
T

Toneyz

The testing amps used in a no trip test is less so not to trip therefore the resistance measured is higher.
 
I'll think you'll find that this will be case with MK RCD's... got caught out this myself. EFLI testing on the supply side would give similar value to that of Ze but Zs was nearly 1 ohm.. turns out that the RCD was adding excess of 0.70-0.80 ohms.

It's a combination of RCD and testers no trip circuitry on my mft1552.

True Zs results can be calculated by subtracting the reading of the RCD input from the outputs and then subtracting that result from your sub circuit Zs.
 
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I'll think you'll find that this will be case with MK RCD's... got caught out this myself. EFLI testing on the supply side would give similar value to that of Ze but Zs was nearly 1 ohm.. turns out that the RCD was adding excess of 0.70-0.80 ohms.

It's a combination of RCD and testers no trip circuitry on my mft1552.

True Zs results can be calculated by subtracting the reading of the RCD input from the outputs and then subtracting that result from your sub circuit Zs.
yes mine is the mft 1730 and mine is adding about .5/.6 ohms, just tried it at my house with a wylex rcd and getting about 0nly .1 ohm.
 
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