Thursday, May 27, 2010 at 16:48
I can confirm testing.
Two RCDs.
- Neither would trip from their inbuilt tester unless they were earthed. (Good! That means it is more than a mechanism
test - it is a full core-balance circuit & break
test. I expect that Standards would have defined it as such.)
- Both tripped when their downstream (Active) was leaked to earth.
That's exactly what I said would happen.
"HOW can the RCD possibly operate IF there is NO path for the leakage back to the source???? Please explain !!!".
I said (or intended) that the RCD itself does NOT have to be earthed. It is only the power source and leakage that have to be reference - ie, the hydro-plant or inverter or genny is earth referenced (staked) as is the human, possum or cat.
The RCD itself only required the core imbalance - and that is between L1 & L2.
Is that clear?
Step 2:
(Hence why...?) "the authorities" do not recommend earth referencing a floating system because you can touch one side of a floating system and you will be fine.
By earth referencing - ie, the MEN system - touching one side is safe and the other is "fatal".
The RCD will only operate in the latter if the toucher has enough leakage to earth. (As you said, RCDs do not protect against Active-Neutral loads - whether they be halogen downlights, human, or appliances.)
Whether to earth or not is an awkward decision - it is a bit like the decision to mandate
seat belts to save lives (but at the time,
seat-belts would save you in 70% of accidents and and kill you in the other 30%).
Similarly for the earthing of
inverters and generators.
For a floating system you can touch either conductor (L1 or L2) without harm. 100% success
In a MEN system, touching one is deadly, the other not. 50% success.
So why create a hazardous situation?....
.... because fault combinations add complexity.
Start connecting other loads and an L1 to chassis fault in one and an L2 to chassis fault in the other means the poor person that spans both chassis is shocked. 100%
hazard.
But the authorities in their wisdom decided that given the average application of (portable)
inverters and generators, it is (statistically) safer to leave them floating.
Hence the earthing "not recommended". (However I expect it is recommended if you are supplying a collection of white goods and other metal-exposed appliances. If you do then do it. It you power PCs, plugpacks, TVs, radios etc, then I also suggest that you not earth reference.)
Whilst RCDs could protect against an earth-referenced fault, the authorities do not regard RCDs as something that should be relied upon - they may fail to operate. (That was their traditional attitude and was still apparent in AS3000:2007.)
And as we have agreed, RCDs will not protect against a 2-line fault - ie, L1 to L2 or Active to Neutral - aka a "load".
Does that clarify what I have been trying to say?
If it doesn't, then all I can suggest is have another look at the link you posted. Else read up on RCD operation and understand how the MEN distribution system works, and why.
If you want the Authoritative source, refer to AS3000. If it contradicts what I have said, please quote the relevant section AND its context. (I don't have ready access to SAA publications at the moment.)
Or to repeat the
test I did and tell me that an RCD does NOT trip if it is not earthed. (Use a resistor - not an organic breather.) (PS - I used mains, not inverter etc.)
And now I have just been told that I have a duty of care on this issue.
This site has apparently gone against the recommendations of regulations and authorities and have allegedly been so informed.
(I think that's what I was told - obviously a reference to what I said above...)
Is this site incorporated? LOL!
Oh
well, this site is safe unless someone follows the earth stake recommendation and that results in injury. Then authoritative references will have to be provided or argued.
Or has that since changed? I still haven't caught up with recent changes... urghh!
Been away too long - I can't even tell if that verbal was in jest...
And for legal reason, I'll now shut up.
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