Yes, that would be my suspicion for what I suspect is another of those 'urban myths'.
Kind Regards, John.
RCD wiki + Common Misconceptions about RCDs
- Thread starter JohnW2
- Start date
Kind Regards, John.
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As I said, I've heard all this talk about RCBOs being 'more electronic', even though I didn't understand why, or eactly what the difference was meant to be. We're now being told that (as I suppose I suspected) this is not the case, so it would be quite interesting to ask manufacturers for the reason for the difference in 'IR testing warnings' to which you refer.
Kind Regards, John.
Ah! I haven't looked but what I think it actually says is -
remove the RCBO when testing insulation.
This may have lead to a misconception.
Of course the RCCB is not, because of its position, 'in the way' when testing.
EDIT - Sorry posted wrong link
Look at section H in
http://www.farnell.com/datasheets/97298.pdf
remove the RCBO when testing insulation.
This may have lead to a misconception.
Of course the RCCB is not, because of its position, 'in the way' when testing.
EDIT - Sorry posted wrong link
Look at section H in
http://www.farnell.com/datasheets/97298.pdf
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No I now take it to mean remove RCBO when testing the RCBO itself.
I'm totally lost. Could you perhaps try to spoon feed me with what you are trying to say (in this and related posts)? Thanks.
Kind Regards, John.
Yes, sorry about my edit. When I had another look the wrong bit came up.
As to the discussion -
When seeing the notice "remove the RCBO when insulation testing" (or words to that effect) I, and everyone else it seems, assumed it meant that the RCBO would be damaged.
Although it does say "When the installation has been completed",
I take it to mean the opposite in that it would appear to be a process to test the RCBO itself which lf still connected to the installation would/may lead to false results for both. Would you agree?
As to the discussion -
When seeing the notice "remove the RCBO when insulation testing" (or words to that effect) I, and everyone else it seems, assumed it meant that the RCBO would be damaged.
Although it does say "When the installation has been completed",
I take it to mean the opposite in that it would appear to be a process to test the RCBO itself which lf still connected to the installation would/may lead to false results for both. Would you agree?
Indeed. It's having seen/heard everyone apparently believing that which led me to also assume that it had to be true! As I've said, I've never seen anything 'official' in writing which confirms such a belief.
Well, I'd certainly agree that the notice is very bad, since we are all struggling to understand what it means - and it's at least possible that nearly everyone has been misinterpreting it - a 'notice' could hardly fail its intended purpose more comprehensively than that! My problem with what you say above ('process to test the RCBO itself') is that I would not have thought that would be a process one would normally undertake - at least, not routinely. You don't do that with MCBs or RCDs do you, so why for an RCBO?
On the basis of what the intstruction leaflet says, I would have interpreted all this as simply 'warning' us that if we do test a circuit with an RCBO connected, we are going to get low N-E IR readings because of the RCBO - i.e. implying that we should remove the RCBO if we want to be able to get true readings of N-E IR for the circuit concerned.
Kind Regards, John.
Agreed.
I just surmised that if the RCBO did not have these readings it may be faulty.
However, I can find no similar document relating to RCCBs so more likely a warning simply because of the earth wire on RCBOs and the relatively low N-E resistance,
I just surmised that if the RCBO did not have these readings it may be faulty.
However, I can find no similar document relating to RCCBs so more likely a warning simply because of the earth wire on RCBOs and the relatively low N-E resistance,
Yes, I'm sure you're right - but, as I said, I don't think that IR testing of an isolated protection device (of any sort) is something one would nortmally do - unless out of interest, when one had already decided that it was faulty.
Yes, Of course, I've been slow in twigging that. Since the only problem IR measurement on a circuit with an RCBO connected is apparently the N-E one, the same can't possibly happen with an RCD, since it has no earth connection. I reckon that's wherein the myth was born!
This one definitely has to go in the 'misconceptions' wiki, I reckon
Kind Regards
Now that's an interesting difference I had forgotten - and I wonder why it is ?
The RCD protection function itself does not require an earth, and I'm fairly confident the earth wire on an RCBO is only used for generating a test current imbalance*. So I wonder why they decided to do the test current to earth in an RCBO but to neutral in an RCCD
* It's also possible it's used for some noise filtering, but again, no logical reason it's not also in an RCCD.
It may be that the "functional earth" for the RCBO is used to operate the disconnect if the potential between earth and neutral rises too high suggesting a fault in the earthing system.
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