To test, or................

[Brian Kirby]

As a certain comedian used to say, “I wanna tell yer a storee”.

I invariably test site electrical supplies with a W4 mains tester before using them.  On our most recent wander around Northern Portugal and Spain, we encountered about 50% reversed polarity connections - so, no great surprises there, and little had changed since our last visit four years ago.  However, due to its electrical system, reversed polarity is not a concern with our van.

More importantly, on one site, at Cubillas de Santa Marta (Spain, on the A62, between Valladolid and Palencia), I encountered one connection with earth and live reversed!  Hmmmmmm!  Fortunately, changing to the next socket down resolved that problem.  Still, worth knowing about before using the supply, no?

Our next stop was Logroño (Camping La Playa).  Finding no earth on the first socket at the nearest pillar, I tested the next seven with the same result.  So: I tested the next nearest pillar, and the tester indicated a satisfactory earth.  Next day, after some comings and goings on adjacent pitches, I re-tested the supply to check no-one had tripped it to find that, whereas the supply was still live, there was now no earth.  As we only had the fridge and on board battery charger connected, I decided to leave well alone and go off to play in Logroño, but to re-check later on if others arrived.  However, before leaving, I checked every socked on that pillar, and all showed no earth present.  That evening, one of the morning departures returned, so I re-checked our supply after they had settled back in and, to my considerable surprise, our earth connection had returned.  No one else was connected, just the two of us.  Thinking his van may have a fault, I approached the owner, whose English was good, and told him what I had discovered.  I suggesting that, especially as they had a small child, he may wish to get his van electrics checked in case the fault lay there.  His van was a new acquisition, but second hand, so he agreed this would be wise.  The next morning he left – again taking our earth with him!  However, by now curious, I started to prowl around the site looking at things electrical, and what I saw did not inspire confidence.  To give a flavour, site lighting columns were connected via exposed screw terminal blocks, with the earth wires just cut back and not connected.  It seemed to me that wholesale DIY modifications had been made - including various branch supply connections to rental cabins made via screw terminal blocks and then merely taped over - and that the installation would have been condemned outright if subjected a proper check.  Later that day, two more vans arrived and connected to “our” pillar and, lo-and-behold our earth returned.  The next day we left!

So, after the story, two questions for the electrically expert.

1.    Can anyone please explain what sequence of connections could possibly explain the appearance of an earth connection when two or more vans are connected, via different sockets, to a pillar, that otherwise shows no earth available?

2.    With the very important proviso that a van has a working RCD as its main switch, is the absence of an earth really a significant safety issue?

I ask this last question because, as I understand the operation of an RCD, if the current flowing through its live and neutral terminals is not in virtually perfect balance, it “assumes” an earth fault, and immediately isolates the supply - whether or not an earth connection is present.  If this is correct, do RCDs now make the earth connection somewhat redundant as a safety feature?

[Minstrel]

In Britain we are not allowed to do electrical work in our own homes (who takes any notice of that rule). It seems that other EU member states don't worry about safety much!

[Chudders]

Brian , What a complex subject this is. In my opinion, no an RCD does not negate the need for a satisfactory earth. If for instance you have a live fault in your van and the van chassis or structure becomes live you may not know it until you perhaps get out of the van and complete the circuit from live through you, through the mass of the earth back to the supply transformer. An RCD detects the imbalance when part of the current is leaked to earth. There is also the reliance on RCD,s a as a mechanical device to provide the disconnection. There is an established failure rate in RCD operation but at the moment I can not remember what the percentage is.

The new wiring regulations in this country (17th edition ) have placed a greater reliance on RCD,s and a possible reduction in earth bonding (Bathrooms is an example). Many in the trade do not feel that this reliance solely on a mechanical device is entirely satisfactory.

Caravan sites in this country in order to comply have to be earthed with what you probably know is a TT system. This is the earth stake system at each point with the stake being driven in to the ground to provide the fault path back to the supply transformer. These have to provide an earth fault loop impedance within acceptable limits at each point when tested in order to provide a satisfactory 'disconnection time'. Caravan sites should not be connected to a PME (TNC-S) system in particular as found in many urban areas. Reasons can be explained if you wish. This is where the earth route to the transformer is derived via connection to the neutral and is very common. If you live in a town etc this is probably the system you have.

I am certainly aware that some continental sites have no such requirements and are very lax in their electrical supply safety.

I have heard that some people with touring caravans/motorhomes knock a metal tent peg into the ground and connect it to the vehicle chassis. This is extremely unlikely to provide a satisfactory earth fault loop path. Stakes etc can require to be driven in in many cases for several feet etc and even then sometimes multiple stakes are needed and it also depends on the nature and moisture content of the ground. In any event if you do not have a an earth fault loop impedance tester you would have no way of determining its effectiveness.

Personally I would not connect to any system without what appears to be a satisfactory earth even with RCD,s. Even the plug in testers that many use don,t verify a satisfactory earth only that an earth of some description exists but that is argueably better than nothing. Caravan sites in this country do require testing at regular intervals as a licensing requirement.

As to why your earth seemed to appear when other vans were connected I can not think of a reason at this time but will give it some thought.

I recommend that on motorhomes/caravans a check is made that polarity is correct and that an earth of some description is present and a regular test of RCD,s by pressing the test button. (6 months minimum between tests.) RCD,s at home should be regularly tested similarly.

Regards, Dave

[colin]

Minstrel - 2009-10-23 10:28 PM

 

In Britain we are not allowed to do electrical work in our own homes (who takes any notice of that rule). It seems that other EU member states don't worry about safety much!

 

The regulations provide for certain electrical work to be done by the house holder, other what is considered more safety critical work is to be done by competant persons and/or signed off by a qualified person, I myself was deemed a competant person such that I could wire up the new bungalow provided it was checked by a qualified person, other EU countries like France have had strict laws regarding employing electricians for longer than us, others such as Greece and Spain seem not to worry judging by some of the instalations I've seen.

[Chudders]

Minstrel, I do agree that much electrical work is done by so called non competent persons such as the householder. It is Part P of the building regulations that require the work to be carried out by a competent person and an appropriate electrical installation certificate issued. The usual manner of proving competence is membership of one of the bodies authorised by the government to register suitably qualified persons. These members are then inspected themselves at least annually after having provided the required qualifications. There are other possibilities for proving competance but these are rare. There is one other route for a householder to go and that is to pre notify the local authority building control that such work is to be done including provision of details and plans of the work and payment of a fee. The work will then be inspected by a person nominated by the local authority at various stages. ( I am one such individual who carries out such inspection and testing on their behalf, (but I do not work for them.)

Whilst I agree that much work is done by householders etc with no certification difficulty will arise when the property is to be sold. The searches will require the vendor to sign to the efect that no 'notifiable' work has been carried out without the required certification.

Around the same time as the introduction of Part P the european harmonisation of cable colours came in to being and were changed from red and black to brown and blue. It is likely therefore that if there is wiring in a property with the new colours it may well have been done since the introduction of Part P.

At the time there was a clamour at wholesalers to buy up cable with the old colours for this reason.

I am in the trade and before you jump on me regarding all this regulation may I say that I do not agree with the operation of Part P. It was supposed to stop what were referred to as the cowboys from doing unsafe work but in my opinion for a variety of reasons has had the opposite effect.

My apologies Brian, this thread has gone of topic somewhat.

Dave

[Chudders]

My above posts suggests RCD tests at a minimum of 6 months. Quite why I said this I do not know, it should in my opiion be a maximum time between tests of 3 months

My excuse is that it was getting late.

Dave

[Clive]

For an earth fault to be of significance there has to be some part of the supply connected to earth initially. This is normally the NEUTRAL of the supplying transformer at your local substation. (This is normally the case in most of Europe but not necessarilly in Norway where some supplies are different.)

 

When you have a FAULT in your van then what happens is that some of the current you are taking from the mains returns to NEUTRAL via the EARTH FAULT and not up the dedicated NEUTRAL wiring. Hence there is an unbalance between LIVE and NEUTRAL currents because some has returned via EARTH. If this unbalance is more than 30milliamperes then the RCD should open and disconnect both your LIVE and NEUTRAL supplies.

 

Lots of TESTERS rely on the EARTH connection being correct and check the voltage between LIVE and EARTH and NEUTRAL and EARTH to ensure that there is very little difference voltage between NEUTRAL and EARTH.

 

If there is a lot of current (AMPS) flowing back to the substation via the NEUTRAL wiring then there will be some moderate voltage drop in the wiring which can confuse some testers.

 

Some systems (e.g. Sargent) include reverse polarity indication but are confused in unusual circumstances. Like Norway where some supplies are fully isolated so that there is no initial earth connection or again in Norway where some supplies are bonded to earth at the substation mid way electrically between what we call LIVE and NEUTRAL so there is no right way round.

 

On a site where there is no EARTH connection at the hookup post and the supply is NOT bonded at the local sub station and several vans are connected to it you have a potentially dangerous situation. The first van which has an earth fault will provide the initial earth bonding. The second van to have an earth fault at a different voltage (like part way along a water heating element forexample) will then provide a second earth fault and a fault current will flow between the two vans via the joining earth wiring.

 

If either of the vans has an RCD which opens both L & N supplies then the fault current will stop when the first RCD opens.

 

Hope that helps

 

C.

 

 

 

[mondo]

So would a reverse polarity adaptor stop the above or what

[rupert123]

Personally I have better things to do than wander around campsites checking every hookup point until I find one that suits. In France this year, on three sites, someone came and connected my lead anyway and locked up the box so you had no choice. I have never ever checked for an earth and certainly would not bother about reverse polarity. I do have an RCD so just let this do it's job if needed. Now I am aware their is a 1 in a hundred million chance of something going wrong but has anyone had a personal experience of a serious problem caused directly by a hookup point being wrongly wired. Get a life folks, start enjoying your holidays not going around looking for an accident to happen.

[Guest Tracker]

Maybe it is a little unkind to condemn in such a cavalier fashion Brian's efforts to enlighten us all to the potential perils of mains electricity?

 

Knowledge is power, allegedly, and although we very rarely use EHUs I would like to thank Brian and others for keeping us all aware of the potential perils.

 

What does the sign say on electricity poles?

 

Oh yes - I remember - DANGER OF DEATH - so no real risk then Henry!

 

Maybe noone has ever been electrocuted or had their van burn due to an on site fault but I have no wish to be the first either!

[Clive]

I,ve had 11kv up my arm and down my leg due to earth (in a field) to my own stupidity and lived to tell the tale.

I cannot think of anything that will provide better protection than a regularly tested RCD.

 

C.

 

[Brian Kirby]

Thank you both Dave and Clive for your explanations. 

Regarding the desirability of a safety earth connection, I understand the point regarding possible malfunction of the RCD and, in view of this possibility, the undesirability of  relying solely on this for protection.  I did test the RCD when I found there was no earth, just to assure myself that it still responded to the test button, and took some comfort from the fact that it tripped as intended.  How conclusive that simple test is, I know not!

However, I'm still mighty puzzled by the on/off earth syndrome.  At first I thought the other van must have neutral and earth crossed somewhere, but then realised that the high incidence of reversed polarities I had found would soon have resulted in the earth becoming the positive with, I assume, obvious consequences!  Besides, this notion was totally dispelled when the earth reappeared with different vans connected.  I suppose it is possible that two different vans, of different makes, might have identical wiring faults, but it is surely highly improbable?

Is it, therefore, some characteristic of the type of tester I was using?  I assume some current must pass to earth to prove it's presence, but less than would cause the RCD to trip?  I also assume this must involve bridging both live and neutral to earth, so as to test polarity?  With no other van connected, or with just the tester connected directly to the pillar, no earth showed.  So, no current flow to earth from either live or neutral.  When another van connected, it will make connection to its pillar socket's earth terminal.  When I then re-inserted my tester into one of our van's sockets, the test current must have been able to flow to earth by some route, as it then indicated the presence of an earth.

I assume (because I eventually tested all the sockets directly with the tester, and not via our hook-up/sockets) that there can in fact have been no actual connection to earth via the pillar.  However, I wonder if somewhere within the pillar the earth/neutral terminals might have been crossed, or combined, so that connecting another van enabled my tester to "see" an earth via its neutral connection?  Presumably, a fault of this nature would have satisfied both vehicles on-board RCDs since, the fault being in the pillar wiring, the current flowing on both lives and neutrals would have remained in balance?  Wrong tree?

And no, I'm neither going around looking for electrical faults (just wishing to confirm their absence) nor, I'm afraid, particularly trying to educate others on their risks.  I'm just rather selfishly wanting someone with sufficient knowledge to explain how what I saw might be possible, so that I can understand what was going on.  I'm just curious, that's all.

[tonyishuk]

Begs the question should / could you use a RCD when using a 12V to mains inverter ? (I assume its the voltage what does the damage to our fragile frames, not nessecarly the current)

 

Rgds

[Clive]

Without knowing exactly how your tester works and seeing its internal connection diagram suggestions why you saw what you saw can only be conjecture.

 

I do not carry a reverse polarity tester nor a swap over lead in our van, nor do I intend to. What I do carry is a good digital multimeter and a set of tools. Ideal for testing continuity, fuses and the presence of voltage.

I have never yet felt the need to use these associated with any hookup supply in the UK France, Germany, Belgium, Holland, Italy, Spain (close call here though) or Australia. Our van has an RCD which for me remains sufficient. As did the hire van in Oz. The display on the microwave oven illuminates as soon as the hookup is connected. Our previous van had a small neon light indicating the presence of the mains supply.

 

But lots of companies make a living selling and fitting these testers!

 

Its your decision.

 

But when it comes to the DC 12 volt circuits then the multimeter is most invaluable.

 

Regarding isolated supplies from inverters or generators then earth bonding the NEUTRAL is required if that supply is routed to more than one bit of equipment. If you just say plug a hedge trimmer into your generator then an isolated supply is deemed fine. If however you supply a couple of caravans then NEUTRAL bonding to EARTH should be done for the reasons outlined above.

C.

 

 

 

 

[ALAN G]

My own experience is as confusing as those already noted.

(1) Several times in France and once in Italy I have found Blue CEE sockets with Live and Neutral reversed (but with an Earth) so I now have a reversing connection to get the system back to normal.

(2) The father of my Danish daughter-in-law says that there are no Earths fitted to Danish circuits as each has its own RCD. Certainly many of the sites we hooked up to in Norway, Iceland, Sweden and Denmark had no Earth. This was irrespective of Blue CEE Sockets.

(3) Many years ago we stopped on a site in the middle of Spain which was 110 volts on both the Live and Neutral to earth. Obviously this is safer than 220volts to earth but my RCD didn't like the arrangement.

(4) I phoned the people who make the control unit in my own van to ask about safety when there isn't a site earth. They said they didn't know. They only made the unit having bought the design from another company.

(5) Asking at the Site Reception as to whether there are RCDs in the circuits is usually a waste of time. Peering inside the box you are connecting to doesn't always provide an answer.

(6) I always test and inspect as much as I can before connecting.

(7) The first caravan we owned, and lived in, (1960) had no electricity but it did have gas lights and an anthracite stove. I often wonder whether that was safer than having no Earth.

 

 

 

 

 

 

 

[Brian Kirby]

Thanks again, Clive.  From what you say it seems to me that, provided the RCD is regularly tested and working, and provided both the circuit breakers and the RCD isolate both poles (which ours do), the issue of an absent earth presents no greater risk to safety than reversed polarity itself.  That being the case, I shall follow your and Rupert's example, and abandon use of the W4 tester in favour of occasional use of the RCD test button.  That will make life a little simpler, and I'm grateful for all the explanations.

[bob b]

I connected up to a supply on a municipal site in Portugal a few years ago. Quite by chance, the following day I felt the blue connector attached to my motorhome and it was hot !

I quickly isolated the supply and removed the plug. On examination, I discovered the plastic around the pins was charred. The fault was reported to reception and eventually a guy turned up. He just shrugged his shoulders and wanted to connect me to another supply. I declined his offer and lived off the leisure battery for the remainder of my short stay.

There was no question of taking the faulty supply out of service though. Unlike Rupert, I do check, as far as I'm able to, the safety of the supply when in Europe. 

I also have RCDs.....they didn't trip !

[Chudders]

Alan, as stated above caravan sites are required to have an electricity . supply with earth stakes. ( A TT system). Your van will probably have a 30milliamp RCD whilst the site itself will usually be protected with a 100milliamp RCD, possibly time delayed to provide discrimination.

I carry out inspection, testing and certification. If a site is connected using a system other than a TT system then it will result in an '

'unsatisfactory' report and fail the inspection and test. Hook up bollards in many instances will have an RCD and individual circuit breakers, the RCD can be readily identified by the integrated test button. Interestingly there are now many more requirements following the introduction of the 17th edition of the wiring regs. Things such as a maximum distance from pitch to electric hookup and maximum cable length now exist. (How many times have you seen longer distances requiring two leads to be connected together.)

Dave

[rupert123]

Sorry Brian, I know I tend to jump in with both feet at times, however I stand by what I say about testing. I am an electrical engineer by training, although have not practiced it in years, but do remember odd bits, we all know Clives background and he does not test either. If anyone wishes to carry yet more gear around to mess about in this way fine but I feel the constant posts about non existant problems, remember all the gas attack posts, just serve to worry people with no real facts to back the scare stories up. I know Brians post was just a question about a strange reading but you immediately get the doom merchants going. With all this useless stuff people carry around no wonder they have problems with the weight of their van.

[Brian Kirby]

Not a problem, Rupert, and I hadn't realised you were an MIEE, or I might have paid a little more heed to your comments.

Following one or two shocks in my youth, I have always had a healthy respect for electricity, and have worked with electrical engineers and electricians on many projects.  I have no electrical training myself, but have gained some basic understanding of certain principles from my former work colleagues.  It's a case of a little knowledge, I think, so maybe I've become ultra cautious, and unduly reluctant to place total faith in mechanical (or electromechanical) safety devices where I don't understand how they work. 

It isn't the risk per se that concerns me, it is the fact that in the absence of knowledge of how these devices actually work, I can't judge the nature of the risk, or the likelihood of its occurrence, so can't decide how to respond.  I drive: driving is risky.  However, these risks are understandable, and therefore mostly avoidable.  With this I am happy.

What I don't like, is what I call the Witch Doctor syndrome.  Some unknown (to me - and that includes that whole army of "celebrity" advisers) person uttering mumbo-jumbo, and expecting me to follow his advice merely because he says so.  In other words the man in the white coat, the "expert", who says this or that is safe, or a good product or practise, and I should rely on his advice because he is an expert in a white coat.  Michael Winner on car insurance comes to mind.  Michael Winner on humping, maybe - but would you buy car insurance from this man?  :-)

I just like to know that the "expert" in question actually has some relevant, genuine, proven, expertise, or else to make a rational judgement for myself based on my own understanding of the pros and cons.  So, yes, I'm a member of the awkward squad.