RCD Upstream BG board HIGH LOOP impedance

[sparksfly]

A domestic customer has MK dual RCD board #1 and another BG dual RCD board #2 in loft.
On testing, a couple of circuits (32a & 16a radials) on board #2 had high Earth fault loop impedance ( over 3 ohms for a socket radial). I know that the BG board (in the loft conversion) does not really need dual RCD but interestingly by bypassing its RCDs EFLI drops by 1.4 ohms.

Has anyone seen such high resistances in BG RCDs ?
Has anyone seen high EFLI readings with 2x RCDs covering a circuit ?

BG technical have admitted that only a handful of RCD's have shown high loop readings & that by having 2x RCDs covering a circuit would induce a current in the RCD coil.
I have not noticed, however, that 2x RCD's downstream of each other have ever caused high readings in the past....any experiences/ views on this are welcome.

 

[tony mc]

Its starting to be common and there has been a few posts re this issue.

Once you do a ZS bypassing the RCD you get a much lower result.

It was telectrix on the forum who had a ZS of over 350 ohms on a test and it turned out to be the resistance of the RCD.

 

[telectrix]

Its starting to be common and there has been a few posts re this issue.

Once you do a ZS bypassing the RCD you get a much lower result.

It was telectrix on the forum who had a ZS of over 350 ohms on a test and it turned out to be the resistance of the RCD.

i wanted to test it's resistance to a lump hammer, but the customer wouldn't allow me to.

 

[IQ Electrical]

Tested a cooker circuit on a BG board yesterday, R1+R2 0.04 Ohms, Ze 0.10 Ohms

Text book value 0.14 Ohms.

Measured value was 0.68 Ohms.

Even allowing for a slightly high Megger MFT 'no trip' reading, there is still around 0.4 Ohms of internal impedance on this particular BG RCD.

 

[sparksfly]

Thank you all for your feedback..it is much appreciated.....it does seem that BG do have a known issue with this but like most will not admit is it a real problem. Maybe one day they might pay us for wasting our time on faulty products !!...then again ...... Hey, I just saw a pig fly over my house !!... I think it had BG on its ear...I need a beer.

 

[Knobhead]

From the sounds of things, if that pig had BG on it’s ear it would probably sh*t on you as it passed.
Am I being thick or something but I was under impression that if a manufacturer knows they have a production fault they were obliged to do something about it!

 

[Deleted member 26818]

Perhaps they think it doesn't matter, as the maximum Zs with an RCD is 1667Ω.

 

[malcolmsanford]

Perhaps they thinkit doesn't matter, as the maximum Zs with an RCD is 1667Ω.

That is what I would put down as my Zs and if as IQ I have an R1+R2 of expected values I would not be worrying too much about it.