RCD Test

Thanks for the information RMD. I checked the earths as suggested by taking the plug inside the van and testing for continuity on the outlets. All good. Also checked the lead itself and plugged it into another outlet from the house. I also checked for leakage between the earth and active/neutral wires and all good there. Also no leakage between active & neutral at the back of the RCD.

RCD's generally create an imbalance from neutral to active for the test, earth is not required

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RMD

What you have said is both irrelevant and incorrect.

The installed earthing circuit plays no required function in the proper operation of an RCD. A fault current may flow from an Active conductor via the installed Earthing conductor, or via any other current path which leads directly to the switchboard MEN point. Such event will cause the RCD to trip. In an MEN system, the only event which does not trip the RCD is when current from the Active conductor returns via the Neutral conductor. Any imbalance (over 30mA) implies that there is current returning via an improper route, possibly through a human body to Earth.

If an RCD does not trip when the TEST button is pressed then it is faulty and should be replaced by a licensed electrician. The 'button' test is entirely within the RCD and does not rely upon external downstream wiring or earthing connections

Using an RCD on the output of generator or inverter which is normally of 'isolated' construction will be of no benefit and normally will not trip should there be a current path to Earth. The exception is that if, in rare event, a fault has developed within the generator or the wiring where a fault path has formed between the generator winding, or external wiring and earth. Should a second path develop, such as between the wiring and earth such as a human body contact, then the RCD would offer protective action.

"Checking the integrity of the earth circuit by using a multimeter" as you describe as being "easy" is not a valid test. The requirement for testing is prescribed in 8.3.5 of AS/NZS 3000 Wiring Rules. You should buy the Standard and follow it if you seek to give electrical advice. But get your certification first!

Your expressions (and those of others alike) are not only imprecise but can be dangerous. The danger of fallacious advice in matters electrical can have fatal consequences and should be left to those who are appropriately qualified.

Michael
There you go Michael, all has been corrected!

Thank you Ken. I will order a new one.

Not entirely correct Ken.

The pushbutton test circuit does apply a "load" to imbalance the RCD in order to determine soundness of its operation. The load is in the form of a resistor of value appropriate to induce an imbalance equal to the RCD specification, nominally 30mA. This tests both the electronic and mechanical functions of the RCD.
Such test does not seek "an earth circuit nor its integrity" and does not need to.

Certainly, applying an "RCD tester" at the GPO's does insure that wiring of the entire circuit is correct, but that should have been done at installation.

Hi Allan,

I agree that the “test circuit” does impose a load (via a resistance) but not in the general sense of a load connected to a GPO and any such GPO load is somewhat irrelevant to the test function.

And I also agree that the test button would check that the electronic and mechanical functions operate as required. But as I stated in my original post and to which you seem to agree, it does not check the earth circuit or its integrity.

The point of my post was that the test does not and cannot ensure (not insure) that that the wiring of the entire circuit is correct with respective to earthing and which as you state should have been done at installation.

However many things can change after installation including loss of earth connection somewhere in the circuit.

Many people would assume that if the test function trips the breaker everything is OK.

It may not be OK !

The most important and critical point of my post was that if the “Test” fails to trip the breaker the unit should be replaced.

Cheers, Ken

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Ken, let's get the grammar out of the way first. I did mean "insure". Applying a tester at the GPO is effectively taking out an insurance on the installation. "Ensure" is to make sure it happens—to guarantee it.

As I said,the Test button applies a "load" in order to produce an RCD imbalance. A 30mA load. Absolutely nothing to do with GPO loads.

The RCD and its test function have absolutely nothing to do with the "the earth circuit or its integrity." They are very different entities and not directly related. The RCD has not a responsibility for "wiring of the entire circuit is correct with respective to earthing ".
The interconnected earthing system function is to manage fault current, Active to Earth via the over-current circuit breaker and to maintain zero potential between appliance housings.

Certainly, "things can change after installation" for a number of reasons, but they should not and loss of an earth connection does not impair the RCD function. Many people may wrongly assume that the RCD test function is an assurance of well-being. However it is possibly the only assurance they conveniently have at their disposal.

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Peter,

An RVD (Residual Voltage Device for the un-initiated) does operate on a different principle to an RCD, but in terms of safety does not offer any protection not provided by an RCD where return current is as a result of passing through a person's body.

In the case of isolated generators and inverters, unless faulty and having a fault-to-frame, current can only return via the alternate live conductor so no bodily connection from conductor to earth is at risk.
Should the generator develop a fault between its wiring and earth, then a body comes into contact with the opposite conductor and earth, a current may flow through the body. However, the presence of an RCD in the circuit would detect this and intervene.

Razzle-dazzle is sometimes used to promote the virtues of RVD's but in reality they offer no human safety advantage over RCD's. But they do cost a lot more!

I am not a sparky, but I understand that if 2 earthed appliances have faults and you happen to touch both, the RVD provides protection that the RCD does not provide?
Cheers,
Peter
OKA196 motorhome

Well Peter, I'll walk through it.

Firstly, if two metal-cased appliances are "earthed" then they are bonded so no electrical potential can exist between them so no protection is called for. But if they each were not 'earthed' or bonded and one had failed to Active and the other to Neutral, then line potential would exist and a shock hazard is present. It is for this reason that the common bond earthing system is mandated, as neither RCD nor RVD will protect

The RCD has a different responsibility. If you consider its function you will see that it continues to pass current only when that in line-1 equals line-2. It matters not that one may be Active and the other Neutral. If this balance is lost it heralds that the current is not returning on the path that it should and must therefore be taking an alternate path, possibly through someone's body to earth and hence returning to the Neutral at the MEN point in the switchboard. So the RCD terminates the supply. The RVD acts to the same purpose but by voltage rather than current sensing.

The situation where neither RCD nor RVD will protect is where a person comes in contact with both Active and Neutral without contact to the earthed shell of an appliance. This may happen perhaps when servicing an open appliance on a workbench. Or fiddling with a mains operated experimental circuit. I have experienced this a few times and it is not pleasant!

Avoidance is always better than interruption and double-insulated appliances have saved lives, but it is good to have RCD's and RVD's as a backup.

Alan,

I agree with what you have written but I thought the idea of the RVD is that it provides an extra layer of protection by indicating there is a fault of some description.

Example active or neutral is somehow connected to earth wire of the van when the van is running on a generator?

Also if someone was to somehow become connected between active/neutral and earth for instance when on mains and the earth is missing it will trip indicating that one you have a connection between active/neutral and earth and two the earth is either missing or high resistance.

In the case of the mains version it also indicates if the active and neutral are reversed.

In the above case a where the RCD is not working an RVD would also be useless as it relies on the RCD to provide protection, ie the RVD trips the RCD.

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Yes, true Leigh, an RVD does have some features that an RCD does not provide. But they are not essential to the primary function of preventing electric shock. These features are often promoted by the manufacturers of RVD's in their promotions..... understandably.

When a van "is running on a generator" there is no active or neutral to be "somehow connected to earth wire of the van". Generators have their windings isolated from earth.... there is no active or neutral..... they are floating. It is for this reason that RCD's and RVD's are not required when using generators or inverters. Of course, things can go wrong with generators that change that premise. Winding insulation can fail so that it now behaves similar to a MEN system. In such case, use of an RCD or RVD on the generator output adds a layer of protection.

Should "someone become connected between active and earth" then both an RCD and an RVD will disconnect to protect. If the "earth is missing" then there is no case to answer, is there? And no shock occurs and no disconnect from either. The only time they both will fail to protect is when a person becomes connected to both the active and neutral conductors and that should not happen unless they are 'fiddling' with the installation.

As for an RVD indicating a "missing or high resistance earth"....... it may well do so but it is of little consequence in protecting from electric shock. Distributed earthing systems have a role to play in an electrical installation and were once the mainstay in avoiding electric shock. However, they had limitations in that respect and the RCD was introduced to overcome those limitations. The earthing system has become secondary to that and primarily manages circumstances where installation faults occur beyond the protection of the RCD particularly high fault currents due to wiring failure. The RCD/RVD takes care of circumstances beyond the power outlet.

An RVD is not capable of properly ensuring that the earthing system is in satisfactory condition. It may well determine some continuity present but that continuity may consist of no more than a single strand of a flexible cable. It will register as a low resistance but has a very low current-carrying capacity and under fault conditions will fuse and render the circuit open. The RVD indication does no actual harm but can lead to a false reassurance of the installation condition.

As to the final expression of indicating an active/neutral reversal. Again, RCD/RVD protection is still provided. It is what happens when unqualified people work on electrics and is the very reason why double-pole power outlets are mandated.

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Macca, it is a real danger that people who "think they know" are not in a position to realise their lack of correct knowledge. Even presenting them with the truth may not convince them!

@ Maccas - "I just love it when these technical questions end up in a discussion between qualified, certified people and those that think they know what they are talking about. :-)"

Yep - silly old farts fighting it out at 10 paces - I am right, no I am right, no you are wrong, I am an expert in my own mind - gheez.

Early advice was correctly given that the RCD would seem to be faulty so replace - too easy yet the old farts still want to challenge everything.

Interesting perspective Ozzie. What I saw was one ACTUAL expert correcting a previous post (always handy when potentially dangerous topics are being discussed I find) and some further elaboration as other comments were made.

Perhaps the OP 'er could keep a record of all the "experts" advice on here and then if something goes "pear shaped" (and I hope it doesn't) he will know who to sue until their nose bleeds ;)

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Ozzie, I take offence at what you have said.

Certainly, valid advice was given but the RMD made expressions that could lead to a dangerous situation and required challenging. Following questions were essentially directed to me to answer which I did without rancour.

Licensed electricians are required to respond to any situation that they perceive is hazardous. It's part of their creed. But then you would not know that as you are obviously not an electrician and not in a position to recognise a qualified person when you see one.
Go back to watching the Olympics Ozzie.

Bazooka, thanks for your contribution. Most welcome in the event!

I am not responsible as to how you feel.

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Wasn't talking to you. I was responding to OzzieCruiser.
But, as you say, your'e not responsible! lol

Thank Christ you clarified that, I hate the Olympics :) Well at least until they introduce "Dwarf Throwing :):)

Aussie1 I am with you.

I didn't actually name anyone in particular but hey ..............

I'm not naming anyone either Ozzie but nice to see two old farts agreeing, albeit on something totally unrelated to the actual topic ;-).

People who think they know everything are very annoying to those who do. :)
Dave.

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Michael, In your case the test function was not faulty. You pressed it.... the breaker did not trip indicating a failure in protection. What WAS faulty was the automatic protection itself and it may have been so for some time. Unfortunately it is a 'consumer device' and has the potential to fail...... but not to a safe condition. It could be manufactured to do so but would cost considerably more.

At least you discovered the situation before it was called upon to operate. Most people understandably never test their RCD.

And it's the reason MOST RCD manufacturers (certainly the reputable ones) recommend MONTHLY testing. The disruption to electronic devices is the only downside, having to walk around resetting synchronous clocks while modems/routers etc all reboot.

But it may save your life ...

[I have 22 on our switchboard to test. I pick my time.]

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Hi Zippo,

22 RCD's on your switchboard?? ...... Do you live in The Hilton? lol

No, Allan. But I'll send you a pic anyway (of the board) ...

?? Ok that's enough for me. Testing the test with a tester would be very testing.

Is all the argy bargy due to test-osterone

Just checked but nothing came up. It's Goldy brand 2 pole 16amp 240volt 4500watt rcd. Thanks for the suggestion.

Can we presume that you had a licensed Electrician do this for you as there are a multitude of other tests that need to be run to ensure electrical safety and mandatory testing and certification?