Electrical safety

There is a new device (approved) on the market that overcomes the issues of leakage fault protection in isolated supplies.

The device is known as an RVD and is marketed by Safelec. I believe it is a completely Australian designed and developed device although I may be corrected if I am wrong there.

have a look here for more info; Safelec

frank

The web site gives no detailed information about how the RVD works, only that it works in conjunction with the existing RCD protection.

from the little that is on the site, it seems that this ADDITIONAL device places an earth leakage current on the RCD that preceeds it to make it trip......yeh well there the problem is.....unless there is an earth neutral bond preceeding the RCD it wont see this deliberate earth leakage current.

The problems with the portable sources of supply is that there is no earth connection to the neutral at the source of supply.

I do not believe there is any device that can overcome this problem.

cheers

I am not a champion for the Safelec product but it does have interesting features and is an approved device.

It is applicable to Class 1 appliances which have exposed metal bodies. It has no application to Class 2 appliances which are double-insulated. It operates by monitoring the voltage present on the earthing conductor which is connected to the appliance body and tripping the supply if that voltage exceeds a nominated 43 volts.
It provides no protection from personal contact directly between an Active conductor and the greater body of earth as distinct from the wired earthing conductor. This situation is left to the accompanying RCD to protect the person.

Despite what the Bantam has said above, the principle of operation and essential specifications are on the Safelec website. It operates in conjunction with a standard RCD and in the event of a fault condition isolates the supply by tripping the RCD. This is achieved by causing an imbalance current of 30mA to flow between the RCD's incoming Neutral conductor and the outgoing Active conductor in the same way as the RCD's test button works. It does not rely upon an earth connection nor a system earth/neutral bond for its operation. Accordingly the Safelec product has application in isolated supplies such as inverters or generators where no earth/neutral bond exists.

The problem remains ( explain to me why not) that an RCD requires an earth neutral bond on the supply side of the RCD to function.

BY law there is no earth neutral bond in a caravan.

There can be no in ballance and the can be no current flowing in the earth if there is no connection between the neutral and the earth.

There is a vague discription of how the device works on the site but no detailed explanation.

No doubt this device will achive greater sensitivity, particularly under dertain circumstamnces. but it can not possibly protect against an active to neutral shock.
If there is no earth neutral bond and there is no connection with the greater mass of earth.....for all inetents and purposes, there IS no earth........many of the modes of shock become active to neutral paths.

There is just no way arround it.....so much of what we take for granted in the electrical safety in our homes relies on an earth neutral bond and a connection to the greater mass of earth.

NOW..these RVDs may work when the RCD is included in the inverter or generator, because there will be an earth-neutral bond in that generator or inverter.

But if it is a generaotor with no RCD built in there will be no earth neutral bond and the RCD in the caravan will not work.

cheers

Bantam,

I do not wish to contribute to hijacking the original topic and becoming involved in an extensive argument but in the interests of fidelity I will answer you by responding to your points as follows:

1. "By law there is no earth neutral bond in a caravan."
Agreed, and there does not need to be. The Wiring Rules define the specific arrangement of intentional connection between the neutral conductor and earth. In general, this is at one point only in an "installation" at main switchboards. A caravan is not an 'installation' and the distribution board within a caravan is not a main switchboard.
As a generalisation, it is not functionally necessary for an "earth-neutral" bond to be installed in an installation for a RCD to effectively protect. All that is required is an alternate return current path which may be provided elsewhere or unintentionally by a fault connection. Without such path, no current will flow to earth and an RCD will not trip, but then neither can an electric shock occur as no current flows.

2. "There can be no in ballance (sic, read 'imbalance') and the can be no current flowing in the earth if there is no connection between the neutral and the earth."
The original question was in regard to supply from a battery-driven inverter which can be assumed to be fully isolated, i.e. no intentional connection between its live conductors and earth.
In this situation there is no current path and no risk of electric shock due to a person contacting one live conductor and earth. Accordingly, the issue of imbalance does not arise.

3. "There is a vague discription of how the device works on the site but no detailed explanation."
There are technically adequate descriptions of the product on the Safelec website. Your inability to discover them does not mean that they are not there.

4. "No doubt this device will achive greater sensitivity, particularly under dertain circumstamnces. but it can not possibly protect against an active to neutral shock."
No one has claimed that it will protect against active to neutral shock, and incidentally, neither will an RCD or anything else.

5. "If there is no earth neutral bond and there is no connection with the greater mass of earth.....for all inetents and purposes, there IS no earth........."
Certainly, there "IS no earth" as you describe. That is, there is no deliberate connection between a live conductor and earth, but a 'first fault' occurrence can produce such a connection. In this event it is possible for personal contact between the other live conductor and earth to create an electric shock. The presence of a RCD correctly positioned in the circuit would detect an unbalanced current flow and interrupt the supply. An MEN type connection is not a requirement in such situation.

6. ".....many of the modes of shock become active to neutral path."
In point of fact, it is rare that persons become in contact simultaneously with the active and neutral conductors. And there is no current method available to safeguard from such event.

7. "There is just no way arround it.....so much of what we take for granted in the electrical safety in our homes relies on an earth neutral bond and a connection to the greater mass of earth."
The "earth neutral bond" or MEN is not necessary for valid operation of an RCD. If the return current is unequal to the supply current then the RCD will trip. Any difference in these currents indicates that its return to the source is abnormal and possibly through a human body. The return current (or part of it) does not need to be via the installation but can be any alternate path to the source. The incorporation of RCD's is not reliant on the MEN system which has its own benefits and reasons for adoption that are too extensive to discuss here.

8. "NOW..these RVDs may work when the RCD is included in the inverter or generator, because there will be an earth-neutral bond in that generator or inverter."
Totally incorrect. The RVD is not reliant on a RCD or earth-neutral bond within the inverter or generator. This particular RVD does utilise connection to a RCD but only to use it as a convenient circuit breaker to be tripped by the RVD. It can just as easily have a circuit breaker incorporated within the RVD.

9. "But if it is a generaotor with no RCD built in there will be no earth neutral bond and the RCD in the caravan will not work."
If the RVD were installed in conjunction with the RCD in the caravan then the caravan wiring would be protected as intended by the RVD tripping the RCD breaker. Installed earth to neutral bonds have nothing to do with it.

The following reproduction of a diagram from the Safelec website reveals the method of installation and operation of the product. It can be seen how the tripping circuit connects to the terminals of the RVD. More information exists on their pages and can be viewed with just a little endeavour. I am disinclined to further this discussion to avoid a prolonged argument, so Bantam, you may have the final volley if you so wish.

Please explain to me how an RCD that relies on current flowing in an earth or another alternative path back to neutral can work.....at all....when there is no earth connection....not just no earth connection to neutral....which is required but....... no earth connection period.

seriously.....describe the path from active back to neutral by an alternative means than the main neutral, that will result in a current imbalance or deficit that will result in the RCD tripping.

An RCD will not and can not work without an earth neutral bond.

Serioulsy I don't think I have missed anything...I have had this argument before and nobody has been able to describe the path by which an RCD can operate without an earth neutral bond or some alternative path back to neutral.

There has to be an alternative path back to neutral.


cheers

OK, I can see how the RVD may work......but the fact remains most vans are fitted with RCDs alone and people believe they work.

they simply wont with out a connection to a system that has an earth neutral bond.

That is the point of the original post.

cheers

Part of the problem here is your use of the term "Earth-Neutral BOND".
The use of the word "bond" implies an intentional permanent connection between one supply line which is designated as the Neutral. This bonding connector is between the Earth bar and the Neutral bar and when in a network forms part of the MEN system. I'm sure you have no issue with that.

With a fully isolated system such as a generator or inverter, there is no reference between the live conductors and earth, so there cannot be an alternative return path to the source via earth, either metallic or soil. Again, I'm sure you appreciate that also.

The situation that can occur to change the above is if the supply source, (e.g. generator or inverter) were to suffer from an insulation breakdown between one side of its supply and the housing or frame of the machine. This could now be called a "First Fault". Effectively an earthed neutral has been formed, but it should not be termed a "bond". Correct terminology is important in engineering, particularly when safety issues are involved. Now that we have an earthed-neutral situation, any second fault such as a person coming into contact with the pseudo active conductor and some component of "earth" such as the housing of the inverter or the frame of the alternator, even possibly through the soil, will deliver an electric shock to that individual. A RCD positioned in the delivery lines from the power source will detect that there is an imbalance because the return current is travelling via an alternate path (earth) back to the source. Clearly, the RCD will trip.

Certainly there must be some form of alternate current path to produce the imbalance but it need not be by means of an intentionally earthed neutral. There can be many possible scenarios to produce an earthed line in an otherwise isolated system. Any inadvertent earthing of one line will produce the situation described, with hazardous results. It can be as simple as light rain entering the 230v output socket of an alternator and forming a conductive path to the earth pin which is connected to the frame.

The important concept to hold when considering RCD applications is that any imbalance through the RCD indicates the current is returning via an alternative path (possibly a persons body) and it matters not at all how that return is achieved, only that it is happening. The matter of MEN systems and earthed neutrals are other techniques employed to enhance electrical safety but they are independent to RCD's.

K&FT,

Frank, thanks for bring that devise to our attention. It will fit the bill down to a tee.

One of the good things that I can see is, it can easily be retrofitted to older vans or installations at minimal cost. You may just may have to fit a larger din rail enclosure.

Great bit of gear.

Note to other readers.

I told you there are people who don't want to hear this.

This matter has been well canvased and discussed on this and other forums in the past.

The facts, the physics, the standards and the reasons have all been produced and referenced.

There has been at least one person killed because of a failure to understand this very matter and involving a caravan and in Australia.

From my understanding the person killed was known to some members on this forum.

Make no mistake, we all need to exercise particular care when using portabe sources of 240V supply especially arround caravans and campers and especially when more than one appliance is connected to a source of supply.


You can not expect the same level of protection from electric shock you would have in most modern homes and business.

cheers

HI Keith
Good to see you do understand there is a risk level
Especially if you are using multiple class 1 [have 3pin plugs or are plugging the generator into the van power inlet socket
I suggest you contact Wayne of Safelec
& discuss your requirements with him
The Safelec RVD was original developed for exactly the reasons you are concerned about but has gone much futher now
Therere several versions dependent on application

It consist of two componentsa,a RVD which senses when the isolatopn of the generator has been lost due to a fault to earth
[THAT is when the generator becomes dangerous as far as shocks to earth are concerned ]
When that occur.It sets the RCD for actio n& if when that serious 2nd fault from what is now the active, occurs
such as a oerson it trips the RCD
So you actaully have more protection than in you home with a RCD.
But always remember there is noway to protect from shocks if you touch the active & neutral
Only for shocks to earth which are the more usual unless one deliberaty makes contact with the two active lines
Two types:
RVD-EM isbest usually fitted to the generator while if you fit one in the van the RVD-EMR is a better option
So suggest you contact WAyne 2 Safelec & discuss what will be best for you.
Will not be much use talking to most electricians as few are aware of the product yet!


ps Qlds ambulance service has just fitted RVDs to all their ambulances, thrown out the plain RCDs, So I have been told .
You will be safer than in you rown home!

PeterQ

Please explain to me how an RCD works when there is no earth- neutral bond to provide a reference to the RCD and a leakage path.

If the earth wire is not connected anywhere how can any leakage current flow in it.

Serioulsy..this is a hard question and I am not trying to be funny.

If one of these devices is to work there has to be an earth neutral bond somewhere.

The standards preclude there being an earth neutral bond in the caravan wiring.
The standards also preclude there being an earth neutral bond in an inverter or generator that does not have an RCD built in.

SO, where does the earth neutral bond come from....and how do you get that to comply with standards.

The only way I can see one of these devices being of any use and compliant is if it was permanetly fitted to the generator or inverter.

cheers

Bantam, you are correct in that an RCD will not sense an earth leakage current where no EN bond exists.

An RVD is different and to put my interpretation on it, it is a Residual Voltage Device. In that despite there being no EN bond it will sense a leakage VOLTAGE on the earthing conductor. When it does detect this voltage it forces the RCD to trip to open the supply circuit.

It is also my understanding that it will force the RCD to trip when the leakage voltage reaches 43V which is below the permissible touch voltage(50v) in AS/NZS3000.

hope that helps mate.

frank

HI
As Frank has pointed out:
The RVD detects when the isolated supply is no longer isolated
Ie, one line has a leakage or is connected to the earthing system system
Unlike a RCD where that connection/ leakage must occur before the RCD for the RCD to be fully functional ,the RVD detects that FAULT ANY WHERE in the system.
When/If that occur what happens depends on RVD model used.
For low currents ,up to about 5A, & using isolated supplies it can be used to directly open the circuit with that first fault[loss of isolation]

For higher currents it is used in conjuction with a RCD, such as shown in Allan"s post

In that situation:
with an isolated source if a fault to earthing system occurs anywhere in the system, it sets a true EN bond with that fault
That means the system is now an EN system
& the RCD will trip under the usual circumstances for an RCD[ line to earth fault or neutral to earth fault
l
When used with RVD operation there are two models:
[ a] RCD/RVD -EM
, for use with isolated supplies or when the poloarity of the supply can be gauranteed to be to Standards[can be damaged by incorrect polarity]
[b]RCD/RVD -EMR
where there is a chance of incorrect supply polarity
In those cases, the unit will trip immmediately.

PeterQ

The point that no one has specifically pointed out is that the RVD is wired to both the supply and the load side of the RCD.

I was expecting it to be connected to the load side only.

cheers

Hi Bantam
Was there any reason why that needed to be pointed out
Allan's post clearly showed how they are wired when used with a RCD!!
That is also available on their site.

They work equally as well with:
[1]
a floating earth system .
[2
a simple EN system
[3]
An MEN system.


PeterQ

Yes there was.

remember this is a multistrand forum and prior to Alan's post this was not mentioned....AND remained unmentioned till I mentioned it.

This is critical to understanding how these things work.


This is also critical to understanding where these things can be sited.

An RVD can not be installed alone and remote from the RCD..and they will not work with ANY or an existing RCD.

They work with an RCD they are installed alongside..they must have access to both the supply and load side of the RCD.

Why you would even bother marketing these deviced as a stand alone item I do not know.....they must be installed as part of or right beside an RCD and they can not work without one.


now...another matter.

Just like an RCD, they will not protect aginst an active to neutral shock.
a fact that most normal people do not grasp.


they will restore some of the safety that most take for granted iwhen used in portable supplies, but there are a range of hazxards that still remain unprotected.


People still need to take particular care with electricity afrom portable sources of supply and arround caravans.

cheers

Sorry to harp on the point...but is the caravan has no earth neutral bond, and the inverter or generator has no earth neutral bond AND no earth neutral bond has been introduced......the RCD ( not RVD) will not trip.

A large number of poeple use both inverters and generators with their caravans by pluging them into the caravan inlet socket on the side of the van.

both the caravan and the inverter/generator comply.

There is no changeover switch and there is no introduced earth neutral bond and the RCD will not work.

The sooner that all 240v mains appart from a single battery charger is iliminated from caravans the better as far as I am concerned.

we are close to that being a real posibility.

cheers