While investigating higher than expected Zs readings on a final ring, I find I get about one ohm difference across the RCDs in the CU when doing a live test. Ze is 0.1 but Zs on the downstream side of the RCD is 1.1. This is enough to push Zs on the ring out of spec. The actual resistance across the RCD is zero so suspect getting some sort of inductive effect. Is this common? If I ignore/short out the RCD then aren't I defeating the object of the test. Using a new Di-log 9083p tester.
impedence across RCDs
- Thread starter Maximart
- Start date
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RCDs will have some impedance however 1 ohm does seem very high. Are all connections tight? Is it new or old?
I take it you are using a No-Trip tester - these usually do read a bit on the high side and any noise on the network can play havoc with the readings.
You can always go back to basics and do a normal Ze and then add on your (R1+R2) readings.
I take it you are using a No-Trip tester - these usually do read a bit on the high side and any noise on the network can play havoc with the readings.
You can always go back to basics and do a normal Ze and then add on your (R1+R2) readings.
That is what should be done.
The non-trip test is pretty much useless, as the current used for the test is tiny, so any errors are large.
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Brand new Wylex CU, both RCDs showing the same impedance. I was thinking along the same lines as you guys but its good to have it confirmed. Might take it up with Di-log. Technology's great but sometimes it causes more problems than it cures.
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