RCD switching Bollard or Van?

Submitted: Friday, Jan 17, 2014 at 08:11
ThreadID: 105843 Views:2464 Replies:9 FollowUps:36
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Hi Guys,

What RCD should trigger with a fault in a van ie damp external GPO. Should it trigger the Bollard or the Vans RCD?

JD
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Reply By: Malcolm 02 - Friday, Jan 17, 2014 at 09:02

Friday, Jan 17, 2014 at 09:02
I accidently bumped the test switch on our RCD and it tripped both ours and the one in the bollard. Hope this helps.

Mal
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Reply By: Brian 01 - Friday, Jan 17, 2014 at 09:15

Friday, Jan 17, 2014 at 09:15
It would likely trip the more sensitive one.
Since they are both probably 30mA ones then it will come down to which one is the more delicate of the two.
It is unlikely that both will go.
The reason that happened in Malcolm's case is that the test button that he pressed is not actually testing the integrity of the downstream circuitry in the van, it just puts an artificial bridge across one incoming wire and one outgoing wire at the RCD in order to create the imbalance required to operate the mechanics of the RCD being tested.
This act will cause any upstream RCD to also trip.
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Reply By: Racey - Friday, Jan 17, 2014 at 09:52

Friday, Jan 17, 2014 at 09:52
I agree with Brian's comments. The RCD standard requires 30mA units to trip before 30mA and not before 20mA ( I think that figure is correct). Most RCDs on the market trip at around 26-27mA to fulfil the requirements of the standard. If my memory serves me correctly, the maximum tripping time is 10 milliseconds. Therefore with current settings and trip times being all the same, there is no discrimination between the devices. So it's a coin toss as to which one trips first.

The important point is the fault was cleared.

Cheers
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Follow Up By: K&FT - Friday, Jan 17, 2014 at 11:08

Friday, Jan 17, 2014 at 11:08
max permissible tripping time is 40 milliseconds. most will trip at around half that when tested.

frank
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Follow Up By: Racey - Friday, Jan 17, 2014 at 14:44

Friday, Jan 17, 2014 at 14:44
I stand corrected Frank. It's a few years since was directly involved in RCD's and circuit breakers in particular.

Jon
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Reply By: olcoolone - Friday, Jan 17, 2014 at 10:10

Friday, Jan 17, 2014 at 10:10
Any circuit protection before the fault will trip, after the fault it won't.

The RCD on the bollard will trip as it is before the fault and the one in the van is after the fault so it will not trip.
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Follow Up By: Brian 01 - Friday, Jan 17, 2014 at 10:54

Friday, Jan 17, 2014 at 10:54
Not so olcoolone,
The OP stated "with a fault in a van ie damp external GPO" which tends to indicate firstly that it is a power outlet not the power inlet and secondly that it is part of the van, and therefore will be downstream of the van RCD.
ie the van RCD is before the fault.
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Follow Up By: olcoolone - Friday, Jan 17, 2014 at 20:58

Friday, Jan 17, 2014 at 20:58
Sorry, read the original post incorrectly.

Thought he meant the 240v inlet and after reading again outside gpo...... Didn't know caravans had outside gpo's and if they did they should be the waterproof type and not the general unsealed inside type.
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Reply By: Kevin.Hutch - Friday, Jan 17, 2014 at 11:51

Friday, Jan 17, 2014 at 11:51
All good clear info an RCD (Residual Current Device) has a pre-set current differential most commonly 30mA acting if there is a difference of 30mA or more between the active and neutral currents going to ground somewhere downstream of the device.

Not all are exactly 30mA so in series it is luck of the draw which trips first.

The test button creates a residual current, it is a good way to test if power is present. It is wise to test it regularly (ie 3mthly), also wise to check the plug pins are not oxidised on both the van and the cord.

All Aus/NZ vans MUST have an RCD at the point of entry, in case the outlet you plug into does not, as there is still no guarantee that all available outlets are RCD protected.

Incidentally it may not trip when running off most gensets, as they do not have the neutral earthed and no earth connection, so there can be no circuit for the earth leakage current. This is one of the reasons for not using normal household single pole switches in vans.

Kevin H
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Follow Up By: Allan B (Member, SunCoast) - Friday, Jan 17, 2014 at 12:12

Friday, Jan 17, 2014 at 12:12
Kevin,

Re: "Incidentally it may not trip when running off most gensets, as they do not have the neutral earthed and no earth connection, so there can be no circuit for the earth leakage current."

Whilst not disagreeing about that, it should not be seen as a problem or safety issue.
If, as you say, the genset neutral is not earthed, then there can be no earth fault current hence no risk. If there was any inadvertent path from the genset to earth combined with some downstream earth leakage then the RCD would trip at the design parameters.

The use of double-pole switches in vans is an additional safety factor.
Cheers
Allan

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Follow Up By: Brian 01 - Friday, Jan 17, 2014 at 12:53

Friday, Jan 17, 2014 at 12:53
What you say is absolutely correct Allan.
I'm not sure that double pole switching has any relevance to RCD use, but perhaps Kevin will expand on that.
The real problem with gensets, inverters and other isolated supplies is that they do not react to first fault conditions, and while this is no danger when only one appliance (which may have an earth fault) is connected, the danger arises where more than one appliance is connected.
A second fault can present a very real danger of electric shock, and the RCD will not prevent it.
It needs to be understood that plugging your genset or inverter into the general RV wiring causes the RV itself to become the first appliance.
If there is any fault to earth in that wiring, it will go undetected by either the RCD or the MCB.
If you then plug an appliance which also has an earth fault (to the other active) into the RV wiring you could well receive a fatal shock.
The only ways to overcome this danger are to either use the genset/inverter separately from the RV, and only use one appliance at a time, or to have the isolated supply professionally modified so that any downstream RCD will detect that first fault.
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Follow Up By: oldtrack123 - Friday, Jan 17, 2014 at 13:51

Friday, Jan 17, 2014 at 13:51
HI Allan


It appears I am not alone on THAT subject

Hi Brian

Good to have someone who agrees with what I have been posting for years
Sadly many inverter & generator users, do not understand or agree !!

PeterQ
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Follow Up By: peteC - Friday, Jan 17, 2014 at 13:58

Friday, Jan 17, 2014 at 13:58
From my electrical training many years ago it was explained like this. The original RCD's were known as Earth Leakage device. They would use the earth to trip but they found if your house tripped it may also trip your neighbours house if you didnt have a good earth ( thats another long story ). These days they are called RCD's. What they do is measure the current difference between the active and neutral. So if your kettle has a fault and the case becomes active you will get an electric shock if you are touching "earth" and the active part of the kettle. The current does not go back through the neutral but through you to earth meaning there is a different amount of current running between the active and neutral wires. As mentioned around 30ma is the difference required to trip the RCD.
I would be confident in saying it will trip on a generator.
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Follow Up By: oldtrack123 - Friday, Jan 17, 2014 at 14:01

Friday, Jan 17, 2014 at 14:01
Hi
[1]The main reason for DOUBLE pole switching of"transportable Structures" in Aus is for safe isolation!!
Single pole switching may not be switching the ACTIVE, leaving the connected load/ appliance with power.

[2]With fully isolated generators it is to ensure both active lines are switched OFF

[3]Double pole switching is a requirement when any PLUG IN device has an inbuilt switch.{for the same reasons as in [1]}

PeterQ



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Follow Up By: Allan B (Member, SunCoast) - Friday, Jan 17, 2014 at 14:56

Friday, Jan 17, 2014 at 14:56
Peter,

[1] As you say, the reason for double-pole switching requirement is to ensure that you are always switching the Active conductor. But this has been a requirement long before the advent of portable genies. It is even more important where the supply has an earthed neutral which has always been the case in Australian mains supplies.

[2] Technically, it is less important with an earth-isolated supply such as a genny but still a good and safe idea........ and required by regulations.
Cheers
Allan

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Follow Up By: Brian 01 - Friday, Jan 17, 2014 at 14:57

Friday, Jan 17, 2014 at 14:57
Sorry to burst your bubble PeteC.
A generator or an inverter is what is known as an isolated supply in that both active conductors are above earth potential.
Because of this, neither active has any reference to earth and no current will flow to earth even if you connect a wire directly from one active to said earth.
This is why an RCD will not trip on a first fault (and may not even trip on specific subsequent faults) when connected to an isolated supply.
To make an RCD work with an isolated supply, one of the actives must be connected to earth prior to the RCD whereupon that active becomes known as a neutral.
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Follow Up By: Allan B (Member, SunCoast) - Friday, Jan 17, 2014 at 15:15

Friday, Jan 17, 2014 at 15:15
Brian,
The situation that you postulate is not entirely correct.
To present a shock hazard these appliances would need to be Class 1, (single insulated). The problem could not exist if they were Class 2 (double insulated)
Now if they were Class 1 with exposed metal they would each have an earthing conductor connecting via the plug earth pin to the installation earthing system and therefore be "bonded" to each other. Faults on opposing live conductors would then be effectively placing a short on the supply and cause protection reaction from the over current circuit breaker.
Of course, you could postulate any number of simultaneous fault conditions (e.g. failure of the earth bond) at the same time as the two appliance earth faults, but the probability is unlikely. The electrical safety regulations are reasoned on the probability of simultaneous associated faults arising. Sort of "anything is possible but is it likely?"
Cheers
Allan

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Follow Up By: Allan B (Member, SunCoast) - Friday, Jan 17, 2014 at 15:33

Friday, Jan 17, 2014 at 15:33
PeteC,
Earth Leakage Circuit Breakers (ELCB's) operated in an entirely different manner to RCD's and I won't burden the Forum with the detail.
They presented all manner of problems and are well rid of on consumer installations.
For good reasons they are still used in electricity distribution systems in sub-stations etc. but are a somewhat superior device and installation than those used in homes.
Cheers
Allan

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Follow Up By: peteC - Friday, Jan 17, 2014 at 16:03

Friday, Jan 17, 2014 at 16:03
Brian
1. If the generator has an earth wire and an earth stake into the ground we know it will work as its the same as a house. you have the third path.
2. If the generator has an earth wire ( 3 pin plug ) and connected to the appliance earth wire then the RCD would work as you have that 3rd path BUT you would need to be touching active at the same time as the appliance case, however this would normally trip the circuit breaker. If you had one appliance with a fault that made it live and you touched a second apppliance that was OK and earthed you would trip the RCD
3. If the generator did not have an earth wire or ground stake then there is no way the RCD can work. no 3rd wire path. But this would mean that to get a shock from the generator you would have to be incontact with the active and neutral at the same time. remembering the active and neutral is in no way connected to the ground your standing on. The exact same thing would happen in a house, if you grab the active and neutral at the same time your dead. Many people assume if you stick 2 pieces of metal in a power points active and neutral with each hand at the same time the RCD will work. No it wont unless you are grounded to earth, only the circuit fuse will blow but you will probably be dead by then.

Allan , sounds like we are on the same page and feel free to correct me. Didnt know they still used ELCB's anywhere. If you didnt know they are also starting to introduce 10ma RCD's now, our company specifies potable ones now for site works.
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Follow Up By: Allan B (Member, SunCoast) - Friday, Jan 17, 2014 at 16:17

Friday, Jan 17, 2014 at 16:17
PeteC,
10mA RCD's have been a requirement in hospitals and some other applications for many years.
Cheers
Allan

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Follow Up By: Brian 01 - Friday, Jan 17, 2014 at 16:18

Friday, Jan 17, 2014 at 16:18
Quote "To present a shock hazard these appliances would need to be Class 1, (single insulated). The problem could not exist if they were Class 2 (double insulated)"
Not true Allan, consider insulation damage to two cords of such class 2 devices where a different active is exposed in each case, or only one class 2 device where both actives are exposed.
Coming between those two exposed wires will present a shock hazard.

With regard to the 2 faults on class one equipment tripping the overload device, you are quite correct, however , consider the old knife in the toaster scenario.
If the first fault is in the van wiring (which is most likely considering some of the abominable jobs that some manufacturers do) causing the frame and therefore the outer earthed case of the toaster or the nearby electric kettle to be live, then touching any of those while inserting the knife could be fatal.
Only one electrical fault there, but a deadly situation no less, and people regularly stick knives into toasters.

Consider another very possible scenario of a chap doing some maintenance under a van in which he resides full time away from grid power, he uses his isolated genset for 240v stuff.
The van has an existing earth fault to frame in one active which will go undetected as long as he doesn't plug into the mains.
He is using a class 2 double insulated drill which has an exposed other active in the cord. He grabs the lead to pull the drill closer whilst touching the chassis of the van.
His wife notes that she hasn't heard any noise from him for a while and goes to investigate.

I know that we can, as you say, postulate all sorts of unlikely scenarios, but it is surprising how often that sort of thing actually occurs, and why the rules are as they are.
If it weren't for allowing for what may be considered unlikely happenings, the rule book would be half the size it is.
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Follow Up By: Allan B (Member, SunCoast) - Friday, Jan 17, 2014 at 16:27

Friday, Jan 17, 2014 at 16:27
Brian,
If we were to allow for all "unlikely happenings" then we wouldn't need a rule book......... we wouldn't be using electricity in the first place! LOL
Cheers
Allan

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Follow Up By: Brian 01 - Friday, Jan 17, 2014 at 16:35

Friday, Jan 17, 2014 at 16:35
PeteC.
Let me address my answers to the appropriate numbers of your post.
1. The wiring rules expressly state that you should not use an earth stake in conjunction with a portable genset.
The rules are different for a genset servicing a building site etc where the stake will be installed by a qualified person who will also check the electrical integrity of that earth stake. It is just not possible for the average joe to do this.
Remember that our discussion has equal relevance to an inverter in the van. Where are you going to put the earth stake? How are you going to test that it meets the required impedance limits?

2. Touching earth with your body at the same time as touching a live active will, in most instances, NOT trip a circuit breaker and certainly not in a time frame that would prevent you receiving a fatal shock.
The RCD will not trip if the neutral is not earthed prior to the RCD

3. You are basically correct here but the difference between this example and that of a house is that the first fault will be detected by the RCD in the house, it will not be with an isolated supply in the RV.
It's the second fault that kills.
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Follow Up By: Allan B (Member, SunCoast) - Friday, Jan 17, 2014 at 17:01

Friday, Jan 17, 2014 at 17:01
Brian, Maybe a small point but one that is frequently made in error.
The Wiring Rules do NOT "expressly state that you should not use an earth stake in conjunction with a portable genset."

I don't have the book to hand to quote paragraphs but what it says is that "an earth stake is neither required nor recommended".

In stating that it is "not recommended" means exactly that.... no recommendation is made to use a stake. It is not saying that it is prohibited to do so or that you should not do so.
If you elect to earth the frame of a generator to a stake to perhaps reduce RF interference then there is no requirement to not do so. But it will not improve or worsen the safety situation.

It is not recommended that you stick a knife into a toaster but as you said.... people regularly do it!
Cheers
Allan

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Follow Up By: oldtrack123 - Friday, Jan 17, 2014 at 17:13

Friday, Jan 17, 2014 at 17:13
Hi PeteC

Sorry,you do not seem to understand a number of the points being made
{1] Small portable generators as used by RVers ARE FULLY isolated
[2]That means no NEUTRAL, NO EN link
THAT means a RCD CANNOT function
There is no path from earth back to the lines
[3]AND the Safety recommendation is DO NOT USE AN EARTH STAKE or any other means of deliberately connecting the generator FRAME to mother earth

{"Quote} "it is neither required or recommended"
you find THAT on most site OHS sites

[4] Even with SMALL portable generator that have a
permanently FIXED & wired RCD AS REQUIRED by the STANDARD should not have a from frame to mother. [3] above applies to THOSE as well
[5] Plug in RCDs, in any APPROVED form will not be functional
I say "aproved",because some time back a Brisbane Co was making & selling modified Clipsal power boxes with a nEN connection made in the box itself
Most definitely not able to be approved
A call to Qld ESO saw them quickly removed


PeterQ
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Follow Up By: oldtrack123 - Friday, Jan 17, 2014 at 17:28

Friday, Jan 17, 2014 at 17:28
HI PeteC
re" Didnt know they still used ELCB's anywhere. If you didnt know they are also starting to introduce 10ma RCD's now, our company specifies potable ones now for site works."
ELCBS is the original name used for such device referred to as "earth leakage core balance cbs"

FIRST came on the market around the late 1950 s

10mA up to 500mA RCDs have been available for quite some time.!!

Perhaps you could enlighten us on these NEW
"PORTABLE "UNITS??& how they work with an isolated supply


PeterQ
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Follow Up By: Brian 01 - Friday, Jan 17, 2014 at 17:56

Friday, Jan 17, 2014 at 17:56
A bit pedantic there Allan, I would have thought that any reasonable person would take the authority saying something is not recommended to mean that they did not want you to do it.
I see the term "not recommended" to mean that they do not recommend that you use one, that's much the same as saying don't do it.
This becomes ever more important where it is impossible to test the integrity of that earth stake.
AS/NZS 3001 requires that a portable generator or inverter used to supply a transportable structure shall be of either the fully isolated type or RCD protected where the RCD is incorporated in the supply device itself.
To do this, one active will have to be bonded to the earth pin prior to the RCD, and the rules require that the earth wire be continuous to the structure
This alone would preclude the use of an earth stake as it would have no function, and so they go on to say that a stake is neither required or recommended.
They then go on to show a number of connection scenarios in diagrammatic form, none of which show an earth stake.
A problem arises where someone installs an earth stake and equipotentially bonds that to one active and to the RV earth so that the RCD in the RV is operative. All seems fine except there is no protection offered for an insulation fault in the connecting extension cord as would be offered by an integrally fitted RCD in the genset.
We can argue this all day but the crux of the matter is that driving an earth stake and ensuring that it is functional is just not in the skill set of most genset users, and the reason why such is not recommended.
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Follow Up By: Allan B (Member, SunCoast) - Friday, Jan 17, 2014 at 18:36

Friday, Jan 17, 2014 at 18:36
Pedantic Brian? Yes, it means precise and the Standards are as precise as they can be.
It is a matter of correctly interpreting what is written.
"Not recommended" means exactly that... there is no recommendation.
"Recommended to not do so" means that you are well advised to not do it. But it is not prohibited.
In either case there is no dictate to do anything.
If the Standard required it to not be earthed it would say "The generator frame SHALL not be earthed" just as it uses "shall" throughout the standard.

I would believe that the rule is so phrased as using a local earth electrode is unlikely to provide any safety improvement and may serve to misguide.

As for your "A problem exists....." etc, you really can dream up some unusual scenarios. Why would someone "equipotentially bond an earth stake to one active"? Incidentally, an "active" does not exist in a fully isolated generator as it is constructed. Both outgoing conductors are referred to in Standards as "Live" conductors (see Definitions). Even a (MEN) Neutral cable is referred to as a "Live" conductor. See what I mean about being precise in these matters?

But the forumites must be confused enough. I'm out.
Cheers
Allan

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Follow Up By: Brian 01 - Friday, Jan 17, 2014 at 19:38

Friday, Jan 17, 2014 at 19:38
The lay confusion between both neutral and active being called live is precisely why I used the term active Allan.

Your comment "Why would someone equipotentially bond an earth stake to one active".
The reason why someone would bond one active (live if you wish) to the earth is make the downstream RCD in the van operative. It will not be unless this is done.
An earth stake alone will not make the RCD operative.

I will leave you with your interpretation of the rules as you see it but
saying something is not recommended is very different to not recommending something.
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Follow Up By: olcoolone - Friday, Jan 17, 2014 at 21:04

Friday, Jan 17, 2014 at 21:04
Good to see the white lab coat brigade are at it again!
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Follow Up By: Kevin.Hutch - Friday, Jan 17, 2014 at 22:40

Friday, Jan 17, 2014 at 22:40
Most of the posts have been correct and yes it is a can of worms when trying to protect the unsuspecting van or boat owner with ever increasing numbers of portable low voltage powered devices. This detail is probably more appropriate in a different forum, but as it is here now lets clear up a few misconceptions.

1. RCD's, often called safety switches, are not a panacea to all electrical fault protection. The do require the MEN (multiple earth neutral) convention to be effective. This standard does apply to all grid connected services in Aus/NZ and rarely intentionally missing.

2. RCD's are still today referred to as ELCB's in the USA as there primary purpose is to detect leakage current to earth. Strictly ELCB's measured the current in the earth lead and as that may not be going through a person to ground, is less a personnel safety device than an RCD.

3. Most gensets/inverters do not conform with the MEN convention/standard and its is recommended that they do not so RCD's are irrelevant unless two faults exist.

4. The term active refers specifically to a reference to ground or the earth connection and Live refers to a voltage difference between it and another conductor. If one live connection is grounded then the other is active. If there is no ground there is no active. Hence in a power circuit conductors may be live but not necessarily active. This is the case in most inverters and gensets.

5. In boats it is bad practice to have powered circuits referenced to earth as this leads to electrolysis, so it is not normal to design an active wire on a boat. (Unfortunately misinformed electricians circumvent this creating a fault). It is common to have a form of isolation (cathodic isolator) between any shore ground and the boat earth. Yet when connected to shore power grid it is mandatory to have the neutral grounded on the shore and not the boat the same as with a van.

6. There have been no controls put in place to "guarantee" the "polarity" of AC power cords, hence the double pole switching requirement in vans and boats. Some older double adapters even had the polarity alternated in the two outlets when we had the earth pin up for safety reasons (now it is down with the active clockwise in the socket).

7. Multiple power sources (gensets/inverter/Grid) require specific attention to the grounding of live connections and their switching if electrical safety is to be maintained and ALL "live" connections must be switched.

The original post I believe has been answered by the minor variances in RCD's meaning two in series may trip either but rarely both.

For the rest of the electrical academics, this discussion never ends.

Kevin H
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Reply By: oldtrack123 - Friday, Jan 17, 2014 at 15:40

Friday, Jan 17, 2014 at 15:40
Hi Allan

Yes ever since I can remember as an apprentice in 1945
Did you miss this in my post
[3]Double pole switching is a requirement when any PLUG IN device has an inbuilt switch.{for the same reasons as in [1]}
That is EXACTLY what I meant

PeterQ




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Follow Up By: Allan B (Member, SunCoast) - Friday, Jan 17, 2014 at 15:53

Friday, Jan 17, 2014 at 15:53
Did they have electricity way back in 1945 Pete? LOL
Cheers
Allan

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Reply By: Treading Lightly - Friday, Jan 17, 2014 at 19:19

Friday, Jan 17, 2014 at 19:19
Hi Guys,

Blimey I didn't mean to open a can of worms, but thanks for all the advice, I have a lot of reading to do and things to check.

JD
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Follow Up By: K&FT - Friday, Jan 17, 2014 at 19:44

Friday, Jan 17, 2014 at 19:44
I was going out for popcorn but I may be too late!!

frank
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Reply By: The Bantam - Friday, Jan 17, 2014 at 20:00

Friday, Jan 17, 2014 at 20:00
Point 1 and directly relating to the original post.

When any two residual current or earth leakage devices are active on the same circuit AND an earth fault occurs. Which device trips first or if both trip is very hard to predict.

I did at one time have medical grade 10ma RCD on my electronics work bench that plugged in via a plug and cord into a circuit protected by a 30ma RCD on the circuit.

I have had situations where both have tripped, I have had situations where the 10ma has tripped and situations where the 30ma alone has tripped.

Lets not have a discussion about my work methods and the reasons why the RCDs tripped in the first place......lets say that we all overlook things and that most equipment that ends up on a work bench is faulty....that is why the protection is there.

Which will trip can vary depending on the nature and magnitude of the fault, the relative acting speed of the individual RCDs and the amount of standing unbalanced leakage on the circuit.

What is important is that the RCD is correctly installed and both RCDs trip when tested individually and at least one of them trips when there is a fault or a test introduced to the circuit.


cheers
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Follow Up By: The Bantam - Saturday, Jan 18, 2014 at 00:30

Saturday, Jan 18, 2014 at 00:30
The second thing that is important to understand is that an RCD will only work reliably when it is installed in a permanent structure that is properly bonded to the greater mass of earth.

ALL of our earth related safety measures, and there are several structured into the electrical system and regulations depend on a universal earth bonded to the greater mass of earth.

ALL these measures depend on everything that is not an active conductor and conductive and could become involved with the electrical system being bonded to the greater mass of earth.

Just driving an earth stake does not create this universal earthed situation.....it does not ensure that all surrounding conductive items are earthed.

In fact in many situations driving an earth stake may not even produce an effective bond to the greater mass of earth.

In fact even qualified people with the right knoweledge and equipment have difficulties in some locations creating a satisfactory and effective earth.

So the regulators have decided it is better to be without an earth than one that is poor or not dependable.


Third and very important.
Multiple faukts do occur, and far more frequently than many would like to believe.

I would go as far as to say, most equipment that fails to work has more than one fault.....that is an observation of a repairer.

Further....as one who does testing and tagging.....I have yet to have a session involving multiple items where I have not found at least one item that is not compliant in some way.

The notion that multiple faults are uncommon is to say the least optomistic, at worst is it down right wreckless.


Finally. it is very important to understand that no earth leakage or RCD device can be depended on to work reliably and to the full extent it should when connected to a portable source of supply shich as a generator or inverter....in fact it may not work at all in a large portion of situations.

cheers
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Follow Up By: Brian 01 - Saturday, Jan 18, 2014 at 10:47

Saturday, Jan 18, 2014 at 10:47
Bantam, the only point that I will make is that an RCD does NOT require any reference to the greater mass of earth (being the ground on which we walk) to be effective.
This has probably been the single greatest benefit of the device.
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Follow Up By: oldtrack123 - Saturday, Jan 18, 2014 at 12:09

Saturday, Jan 18, 2014 at 12:09
HI
Ditto to Brian's above post

It does seem that many [including some electrical people]
do not understand the various earthing systems

In the case of SMALL PORTABLE generators using plug in connections[not hard/ permanently wired] connecting to mother earth, sometimes, can have undesirable consequences.
Often the better that connection, the bigger the problem
One problem, possible stray earth currents overloading the flexable earth cable in the lead
Another can be step voltages

PeterQ
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FollowupID: 806503

Follow Up By: The Bantam - Saturday, Jan 18, 2014 at 12:18

Saturday, Jan 18, 2014 at 12:18
It requires a reference to the greater mass earth and connection to a universal earthing system to work as expected in permanent building.

Otherwise it only works on what is directly cabled to it.
It may provide absolutly no protection when other conductive objects become involved with the electrical system.

The single biggest problem with RCDs is that they are considered a universal protection against all electrical shock.....nothing could be further from the truth.

Take for example my work shed, it is a metal structure....that metal structure is both incidentally bonded to the greater mass of earth by its structrual contact and porposely bonded by a driven 4 foot earth stake.
Thus all the metal structure and all connected to it , the slab and the ground around my shed are part of the grounding system and subject to the electrical safety protection measures, multiple.

Should I be using a device, where the cable is cut and the active alone is exposed.....perhaps a piece of steel falls on it, it gets jamed in a steel framed door or some such, the RDC and the century old fuse/ breaker technology will operate.

NOW consider however we have a isolated source of supply such as a generator or inverter even if it has an RCD built in and an earth bonded neutral.

we introduce a conductive metal structure such as a car, trailer, caravan or a wet tent.

All it takes to produce an efficient killing machine is an active fault to one metal object and a neutral fault to another or to the greater mass of earth...the RCD will not operate because it has no earth reference to any of the metal objects or the greater mass of earth.

There was a genteleman killed a year or so back in eaxctly this cenario not long ago.

NONE of our electrical protective systems are as effective or can be relied upon away from a permenent earthing system...AND in some situations they will not work AT ALL.

WE have a big problem because, in our homes and busineses, because of our structured electrical safety system it is very very hard to get a fatal electrical shock..or infact feel one at all.
We are in the second or third generation of general public that have no experience of being sat on their asses by a minor electrical fault or someone they know being badly hurt or killed.

That level of protection can not be relied upon...at all... as soon as we are away from a permemntly installed earthing system.

cheers
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FollowupID: 806505

Follow Up By: The Bantam - Saturday, Jan 18, 2014 at 12:25

Saturday, Jan 18, 2014 at 12:25
I agree that portable source of supply, such as generators should not be earthed, unless they are connected to some sort of permenent electrical system with an earth system.

This is what the standards specify.

Introduction of a haphasard earth has the potential to introduce more problems than it solves.

My point is that we can not rely on the level of electrcal safety in our homes and businesses when we are away from connection to a permenent electrical system and permenent and properly contrived earth system.

We must rely on being particular about our use of electricity and more carefull than we would have been in our homes in the 60's and 70's prior to the introduction of RCD technology.

cheers
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FollowupID: 806506

Follow Up By: Brian 01 - Saturday, Jan 18, 2014 at 13:14

Saturday, Jan 18, 2014 at 13:14
Bantam, An RCD monitors imbalances in the outgoing and return currents, it does not require an earthing medium to do this, all it requires is that one of the incoming live conductors is connected to a protection medium, usually the exposed metal of equipment, but that does not need to be connected to the general mass of earth.
This holds true for a permanent or a portable structure .
This is the great advantage of an RCD over an ELCB for domestic use.

An RCD will only ever protect downstream circuitry that is directly cabled to it.
It cannot protect circuits that originate elsewhere.

Agreed that they offer no protection against intra live conductor shock.

Provided the inverter or genset is suitably modified to allow the operation of the RCD, then you have the same level of protection as is offered in your home (if it has RCD protection) without any connection to real earth.
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FollowupID: 806511

Follow Up By: The Bantam - Saturday, Jan 18, 2014 at 15:04

Saturday, Jan 18, 2014 at 15:04
Mate I know exactly how an RCD works.

RDC..ELCB no matter what you call it and no matter the difference.

Without an earth conductor bonded to the neutral there is nowhere for the current to go but out the active and back into the neutral.
there fore there will be NO imbanance, there will be no difference.

If you have an object that is not connected to the earth the RCD is connected to.....like a metal table connected to the active.
and another object that is not connected to the same earth that the RCD is connected to connected to the neutral such as a tent pole.

One hundred percent of the current that flows up the active into the table thru a human body and back thru the tent pole will flow back to the neutral......the earth that the RCD is connected to is not involved...thus there IS no imbalance and the RCD will not trip.

In fact the only time an RCD not connected to a universal earth is any damn good at all is within the cabling leading to and withn an earthed appliance with a three core power lead.

in a floating portable power supply device, If there is no earth conductor in the power cord and there is no universal earth or bond to the greater mass of earth ..the existance of an RCD on the circuit is completely irrelivent.

for example.
If I have a "typical " metal cassed toaster, supplied from a floating portable supply WITH and earth neutral bond, but not connected to an earthing system.
If I throw said toaster into a bath, assuming all is correct the RCD will trip and in less than the blink of an eye.

IF however the earth conductor of that toaster is disconnected at the plug.
Throw that toaster in the bath now and it will sit there sizzling & generally being deadly indefinitely.....because all the current that flows out of the active has nowhere else to flow but back up the neutral.

In a permanent installation or where the earth is bonded to the greater mass of earth.
RDC/ELCBs provide protection against fauts involving not only the item and the cabling but faults with alternate paths to earth...that is the whole point of them....without this they are pretty well pointless.

If said toaster with the earth lead disconnected was thrown into a metal bath...that realy should be earthed in a building with a permenent electrical system ( another argument), the RCD will trip.



A gen set that is not bonded to the greater mass of earth or to a constructed universal earth situation provides very little protection via the RCD.....with a double insulated device it provides none.

Remember multiple faults ARE common.

cheers
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FollowupID: 806519

Reply By: Treading Lightly - Friday, Jan 17, 2014 at 20:51

Friday, Jan 17, 2014 at 20:51
No there is a response, I think I can understand, BUT I will take all replies on board and tomorrow, over a few quiet ones read and digest and ponder the relative points.

Then take appropriate actions if required.

Again thanks for all replies.

JD
AnswerID: 524698

Follow Up By: Slow one - Saturday, Jan 18, 2014 at 07:43

Saturday, Jan 18, 2014 at 07:43
JD,
Ha, Ha love your diplomacy
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FollowupID: 806480

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