High Earth Fault Loop Impedance readings caused by RCDs

[Engineer54]

Haha, ....Never used the 80% value and never seen a final circuit ever coming close to reaching 70%.

As for any 17th edition test meter, ever being capable of taking a conductor to 70C, you're living in cloud cuckoo land!! An ELI tester injects what 20 to 25A into the circuit for around 2 cycles or 4 half cycles, hardly enough time to raise the temperature of anything!! Who telling you this load of old codswallop??

EDIT.... Ooooops, ....Sorry, i misread your post and read ''are'' for ''were''

 

[GLENNSPARK]

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[sparks1234]

If its Hager, they have a resistance of about 0.67 ohms across the RCD

 

[mhar]

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Sorry, don't understand

 

[spud1]

Sorry chaps I haven't had chance to reply to the initial few questions in this thread and I think the conversation has gone askew from my original question as a result.
I have checked connections on both incoming and outgoing terminals on the RCDs in question and they are fine. Also when I have come across it I have carried out EFL tests on both incoming and outgoing also. The reading has tended to be just under an ohms difference. e.g. 0.15ohms (effectively Ze) on the incoming and 0.98 ohms on the outgoing.
At a high load (e.g. 60Amps) that's a potential spot am I right?

 

[onions1066]

Spud what tester are you using and what make rcd is it?

 

[spud1]

Hi Onions,

I am using the Dilog 9083P MFT and the RCDs where I have encountered this problem haver been CPN and Curve (Denman's own), both low budget RCDs admittedly, not installed by me I hasten to add.

 

[onions1066]

We had a similar problem whilst using a megger in wylex rcds. Megger rep came out and it turned out to be a software problem. No helped you at all but u just thought I'd tell you that.

 

[spud1]

OK thanks for that, interesting.

 

[rattlehead85]

Just as a footnote on this subject if the circuits you are testing are protected by a 30mA RCD the loop values are rendered next to irrelevant as the maximum loop value to ensure disconnection is 1667 ohms.

 

[Badged01]

Just as a footnote on this subject if the circuits you are testing are protected by a 30mA RCD the loop values are rendered next to irrelevant as the maximum loop value to ensure disconnection is 1667 ohms.

You've obviously been sent in to stir up trouble on the forum ........

 

[rattlehead85]

I to have experienced problems doing loop tests on socket outlets using a Kewtech KT64 especially where Crabtree 4293 and Wylex 61008 RCD's are used. Ring tests results and Ze tests give one value but then applying the Zs loop test gives a significantly higher value with the attenuator function switched on. The tester has been regularly calibrated and returned from kewtech with no errors or software issues. Very strange and annoying.

 

[Engineer54]

Just as a footnote on this subject if the circuits you are testing are protected by a 30mA RCD the loop values are rendered next to irrelevant as the maximum loop value to ensure disconnection is 1667 ohms.

I take it, that you don't bother with loop tests then, on a RCD protected circuit?? Let's hope that none of those RCD go belly up when they are needed!! lol!!

 

[rattlehead85]

No of course i do the loop tests after all this is still an essential test for that very reason. I just mentioned this due to some of the previous posts seem to indicate they were concerned about getting higher than usual results even though they still complied.