Actually neither an RCD or RCBO need a ground reference to operate. They (collectively known as RCCBs) work by sensing an imbalance between the live and neutral current and hence earth doesn't enter into their operation. You're probably getting mixed up with the rather ancient and long obsolete ELCB ( Earth leakage circuit breaker) which did indeed sense current flowing to ground via the main earth terminal.
Imbalance is the word or differential. Where is the current path if your supply lines are "insulated" form the environment? The first external component fault will create this imbalance condition but will not be detected since the sum of the currents will still be zero. Only then, further defects will trigger the protection. This is the reason why control voltage transformers also need one of the lines grounded.
he didn't introduce himself on there either.
Thinking about your statement, English is not my native language, when I say ground reference, it's the power supply that needs ground reference, not the RCD or RCBO themselves. They measure as you say correctly, imbalance meaning current went astray somewhere but, to flow back to the power supply, it needs a path and this is where the reference is needed.
Was it the same word for word? Sometimes when I see a first post like that and something 'pings' in my mind I will do a search and will often find the same identical post on multiple forums.I just noticed the OP asked the question on facts as well, I can't tell if he's been back to see responses, none but mine
Still say. If there is no reference, there is no alternative path for the current to leak to "unbalance" the currents. Imagine that the connected equipment has a live wire (no reference no live) short to the metal parts. Voltage would be present and still, the RCD would not detect the imbalance. On regular household applications this is not an issue because the power company has a naturally service ground connected to the Neutral. Sensitive RCD's will even trip from the filtering capacitors on power supplies and motor inverters.
in fact the circuit is essentially what happens in an actual RCD with the resistor D being switched in by the test button and of course RCDs don't have an earth connection, connect up an RCD to a supply running through a mains isolation transformer and it'll still trip.
That is exactly how the included test button works in series with that resistor, and I'm well aware of that. Now draw me a real case scenario where some isolation defect on a load occurs and creates a unbalance to trip the RCDView attachment 77222
Path A through the RCD carries the load current only.
Path B through the RCD carries the load current plus the fault current trough the drain current resistance D. The current through the RCD is therefore imbalanced and will trip the RCD.
The only current flowing is via the live and neutral connections.
No Ground reference needed
I repair valve amplifiers, I typically have to diagnose faults whilst the amp is switched on and internal voltages can exceed 550VDC which is potentially lethal enough without having a mains live and neutral present inside the amp to worry about as well so my 'repair' supply consists of a 1kW mains isolation transformer followed by a Variac so I can adjust the supply voltage followed by an RCD. Because of the isolation transformer I no longer have a live and neutral, just a bi phase floating 240v AC supply BUT The test button on the RCD still trips the RCD open and obviously nothing flows to or through ground or a grounding connection.
I know, I did actually mention that myself
Please explain what you mean by a "Real Case" The resistor inside an RCD is 'REAL' it's not imaginary and it truly exists and it will cause an RCD to trip if connected AND it doesn't need an earth reference.
I'm just pointing out that you are incorrect because there clearly IS an alternative path that'll unbalance the circuit that doesn't require an earth reference or indeed any path to earth at all.
What I'm trying to point out since the beginning is that, if, as per your example, you connect the RCD to an insulated power supply like an inverter or transformer, your load will only connect to the output terminals of the RCD. There is no way it will trip, no matter what defect your load might develop that will make a unbalance "viewed" by the RCD. Your drawn example is not a valid real life situation.I know, I did actually mention that myself
Please explain what you mean by a "Real Case" The resistor inside an RCD is 'REAL' it's not imaginary and it truly exists and it will cause an RCD to trip if connected AND it doesn't need an earth reference.
Take another look at what you posted below...
I'm just pointing out that you are incorrect because there clearly IS an alternative path that'll unbalance the circuit that doesn't require an earth reference or indeed any path to earth at all.
Your knowledge is obviously good, maybe as you say the errors are due to English not being your first language?
Yep, but the fact that you've had to re explain what you meant sort of points out that you got your statement incorrect in the first place, like I said, English not being your first language probably meant that you didn't chose the correct words and that lead to an incorrect statement.
As I've already said, the dummy fault resistor is REAL and it will cause the RCD to trip which you said on more than one occasion wasn't possible because of the lack of an earth. I agree it's probably not likely but I didn't realise we were talking about what was likely if indeed that's what you're implying when you say "real life situation?", I thought were were talking theoretically about whether an RCD needs an earth reference in order to activate and it clearly doesn't.
