# Batteries and Inverter



## leseduts (Jun 3, 2008)

Advice please.
I am fitting an inverter. I understand that I need it as close to the batteries as possible, there is enough room in the battery cupboard, providing I shuffle things around. I have 2 batteries, but do not know if they are fitted in parallel or tandem, can someone tell me how I can tell.
I am then going to wire it up to a straight forward 13amp socket in a cupboard, what size cable should I use from inverter to socket?
Thanks for any help.


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## drcotts (Feb 23, 2006)

Hi
Yes put the interter as close as possible as this reduces the loss of power in the cables.
The batteries will be in Parallel as if there were in series you would have 24v going into everything and would have problems as 12v appliances would burn out of blow up.

You should see the positive of one battery connected to the positive of the other and likewise the negative to negative. Hopefully the connecting cables between the batteries will be thick to minimise losses also.

Consider soldering proper connections to the inverter cables and hard connecting the wires to the battert ie use electrical eyelets instead of the crocodile clips or *** lighter socket. and connect the eyelets to the battery terminals usingthe screws or bolts.

You will probally have one of your batteries that has all the calbe for the van connected to it whilst the second is used as a type of slave. You can connect the inverter to either.

Phill


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## tramp (May 25, 2005)

*a*

hi lesdutt,
ref cable type to plug, bare in mind the output of said invertor and make sure its got plenty ventilation. also calculate what wattage draw through the plug socket and convert to amps the get required thickness cable.

ie: invertor max 1000watts so max draw through plug say 900watts to be on safe side so cable needs to be max 1000w @240v = 5amp max possible twin core as no earth required.

tramp


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## gromett (May 9, 2005)

*Re: a*



tramp said:


> no earth required.
> tramp


Erm? Why no earth? My installation has an RCD, a bridging relay and full earth. The Bridging relay turn on when 240v is applied to EHU. This turns off the invertor (effectively) and brides the incoming EHU earth to the sockets earth. When no EHU connected it bridges the earth to the neutral on the supply side of the RCD. If there is a live fault then then the earth takes the current back to the supply skipping the RCD causing an inbalance that trips the RCD.

My setup is a little different in that the charger and invertor are one unit but the principle is the same I think. Frank will correct me on this if I am wrong as I am stating this from memory without the current circuit diagram to hand.


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## SaddleTramp (Feb 15, 2007)

*Re: a*



gromett said:


> tramp said:
> 
> 
> > no earth required.
> ...


Hi, I have to agree with Gromett here, I have had an inverter fitted and mine is earthed right through, I don't know about the amps etc But mine was fitted at Conrad Anderson so I would assume it was done as it should be and mine definitely has an earth, I am doing a bit of work on mine at moment so been and had a look to check, The earth then goes direct to Chassis.


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## camoyboy (May 9, 2005)

In the original posters setup there is no need for the "earth" connection, what purpose would it have and to what would you connect it to? With the 12v supply from the battery there is + and -, this is all you can connect to the 220v socket.
220v from the EHU is different, then you are using the domestic system where an earth is required.
In a 12v system the negative post is often referred to as earth, but this is more like the return in on mains electric.
Colin
My personal view on the issue only.


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## gromett (May 9, 2005)

12v Is not lethal and therefore doesn't need an RCD.
240V is lethal. An RCD is essential and therefore an earth is required.
I would not use any 240V equipment without adequate protection.

Its up to you if you don't want to have one in your vehicle but recommending to others not to use all safety precautions is a little bit inconsiderate to understate it a little.

Karl


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## AberdeenAngus (Jul 26, 2008)

I think there may be some confusion as the purpose of the 'Earth path' in conjunction with an RCD when used with an inverted supply.

Not going to get into it here because I don't think the forum is a suitable training arena.

Enough to say, with 240v, regardless of whether it is mains or produced from an inverter, is more than enough to kill.

If you are not competent to install such systems, do not attempt it.

In the same way, just because your gas bottles are not on the gas main does not make them any less dangerous.
(not a bad analogy now I come to think of it  )


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## gromett (May 9, 2005)

I am just surprised that two people have come on here and recommended no earth for a 240V system :roll: 

Karl


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## aultymer (Jun 20, 2006)

> I am just surprised that two people have come on here and recommended no earth for a 240V system Rolling Eyes


I have a 'coke can' type inverter. Should I open it up and make a connection from the earth socket in it to ??????????????Earth?

What potential exists between a stand alone inverter and earth?


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## AberdeenAngus (Jul 26, 2008)

gromett said:


> I am just surprised that two people have come on here and recommended no earth for a 240V system :roll:
> 
> Karl


Its an unusual setup with Inverted supplies. There is no traditional "Earth" to speak of as you are hovering above the ground on 4 pieces of rubber.

An RCD trips when it sees a difference between current in the "Live" and "Neutral". Normally this will be because there is a fault current flowing along an Earth path back to the power station (or transformer).

There is also a school of thought that says earthed systems are more dangerous as they only require one fault to be dangerous whereas non-earthed systems require two faults.

Enough to say, isolated systems with no ready earth path are not straightforward and there are a number of ways of tackling them. 
However they should not be attempted if you are not trained.

Experience in normal domestic electrics is not sufficient.

I have some experience of power systems in the desert where there is no ready earth path and you get some VERY strange things happening.


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## gromett (May 9, 2005)

Here is a rough layout of my setup. It's missing a lot of detail. It shows where you connect the earth of the socket to with respect to your RCD.









I wouldn't recommend putting the earth to the chassis especially if going abroad. As the incoming earth from EHU may just be tied to Neutral and this can be volts different to real earth. This would put a potential difference between your vehicles chassis and the ground outside giving you nasty shocks when you get in and out.

On the coke can type inverters don't they provide some form of protect via the earth pin? This will be internal. The OP was asking about connecting his inverter to proper sockets.

I am a qualified electrician, and also have quals in electronics....
My setup is as follows.

EHU comes into vehicle and goes straight to the Multiplus via an input RCD.

The output goes via an RCD back to the distribution unit. 
The multiplus is grounded to the vehicle chassis.

The internal relays operate as follows
If EHU is present it disconnects the vehicles chassis from the earth and applies the EHU earth.

If EHU is not present it connects the earth to the vehicle chassis and to the neutral output.

After much research on this subject before installing the system I feel this is the best way to operate as it rules out human error.

Karl


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## gromett (May 9, 2005)

AberdeenAngus said:


> Its an unusual setup with Inverted supplies. There is no traditional "Earth" to speak of as you are hovering above the ground on 4 pieces of rubber.
> 
> An RCD trips when it sees a difference between current in the "Live" and "Neutral". Normally this will be because there is a fault current flowing along an Earth path back to the power station (or transformer).


I did explain this in my first post about attaching the earth to the neutral on the supply side of the RCD. Solves that issue.



AberdeenAngus said:


> Experience in normal domestic electrics is not sufficient.


Correct, and unfortunately most AutoElectricians do not have necessary experience of 240V systems  It really is a specialist area.

Karl


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## AberdeenAngus (Jul 26, 2008)

Gromett

Your set-up would certainly answer the question "where to put the earth" but I am not sure which failure mode you are protecting against.

Under what circumstances would the RCD trip ?

I assume the fault would be 'Live to Frame'.

But, with an Inverted supply, is there really any difference between the 'Live' and the 'Neutral' ?

With your set-up, you have tied the load frame to the 'Neutral'

Could it be that your protection introduces an equivalent fault to the one that you are protecting against.

Also, what are the consequences of 'Live to load frame' ?
I would suggest nothing. The same as 'Neutral to load frame'.
In fact the only dangerous failure mode would be two concurrent failures, one of which would be "Live or Neutral to frame".
But your system introduces this as a matter of course. 

I would therefore suggest that there is a choice between two scenarios.

With no earth, you need two concurrent faults to produce a dangerous situation, but we would not know if the first had occured.

With your arrangement we are deliberately introducing one of those two faults so that we may trip the supply if the second should occur.

Both strategies address the risk of an incident.

One relies on low likelihood of two faults occuring.
The other relies on mitigating the consequences.

Both are equally valid.


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## gromett (May 9, 2005)

AberdeenAngus said:


> Gromett
> One relies on low likelihood of two faults occuring.
> The other relies on mitigating the consequences.


I am not familiar with your terminology to be honest but I think I understand what you are getting at.
I prefer to force a system into a known state rather than rely on having two unknowns be capable of causing a fault.

For example in a no earth situation where someone doesn't earth the chassis of their inverter which is in the garage for example. It could be that the metal winding pole for the awning falls across the inverters chassis causing it to be 'earthed' to the chassis or a can of coke rolls and wedges between the case of the inverter and the chassis etc etc. If there is then a live fault in the equipment in the hab area. The user touches the equipment while also touching any part of the chassis...... Sounds unlikely that this number of events will occur but you are relying on 'unlikely' for protection.

My way is to force the system into a known state where only a limited number of failures can cause problems and then as you say mitigate (I call it protect myself).
As my chassis (off EHU) is grounded and the neutral is also bonded (via a relay) to the chassis the RCD will operate in any live fault condition.

One method relies on multiple faults not occurring, the method I prefer puts the system into a known failure state and protects against that failure.


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## AberdeenAngus (Jul 26, 2008)

My terminology come from a Risk Management based approach to hazards commonly used in the Nuclear and Oil & Gas industries.

Whilst this is perfectly valid in an environment where Risk Management is an accepted way of working, I can understand where you are coming from.

No obvious answer....Horses for courses I guess.

One last thing.
Having forced the system into a known failure state,
have you considered the likelihood that your protection won't work ?
Recent studies show that RCD's can fail to trip 7% of the time but this drops to less than 3% if tested regularly.

So the lesson is, if you're fitting an RCD, test it regularly.


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## gromett (May 9, 2005)

That report was back in 2006.

An update to the report reveals a failure rate of 23 out of 607.
However a number of these were failed because they had been shorted out because they kept tripping so this is a positive failure. If you remove these positive failures which are not a risk then the failure rate is only 2.8%.

Pretty small sample but the figure is much better than the original 7.1%.
They also state this figure would be reduced further with regular testing.

I prefer the 2.8% possibility of failure combined with the small chance of a fault to having the multiple unknown fault situation of having an unearthed system.

Karl
http://esc.org.uk/news-and-events/research/industry/rcd/january-08.html


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## AberdeenAngus (Jul 26, 2008)

Oooookay,

So about 50% of the failures were "Evident" and 50% "Hidden" which sounds about right for this kind of device.

For this type of electro-mechanical component, the failure rate distribution is random against time i.e. 1 yr old units are just as reliable as 5 yr old units;

Given an average value of 2.8% dangerous failures on demand;

Assuming a normal distribution, therefore 50% will be above this figure, 50% below;

In order to achieve a 90% confidence envelope, you would need to take a factor of (about) 3x the average failure rate.

Therefore you are looking at about a 90% chance that 1 in 12 RCD's fail dangerously on demand, excluding the ones the "Electrician" had shorted out (makes your blood boil - don't it).

Protective equipment fails to protect, frequently. That's why we test them so often. This probability of failure should be taken into account when considering the best course of action.

At the end of the day Reliability is a theoretical concept. What is more important is Availability. i.e. is it going to protect you when called upon ?

Availability of this kind of device is proportional to how often it is tested.

Like I said, IF you fit an RCD, test it often.
But fitting an RCD is not a perfect solution or the only approach.

Horses for courses. QED.


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## aultymer (Jun 20, 2006)

> On the coke can type inverters don't they provide some form of protect via the earth pin?


Could the qualified electrician with electronics experience answer this please?
The 'coke can' inverters have no connection other than to the vehicle battery.
What is the dangerous potential between this type of inverter and earth?
What is the potential between any stand alone inverter and earth?


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## sallytrafic (Jan 17, 2006)

Can I just introduce a note of realism concerning coke can type inverters. What is their output, does 75-100W sound right? What three pin devices ie with a functional earth are there at that low wattage that a motor caravaner would plug in, the only thing I can think of is a old fashioned metal caged wander lamp. Everything else is a double insulated device with no earth.


or am I wrong?


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## DABurleigh (May 9, 2005)

I nailed my colours to this topic's mast here:
http://www.motorhomefacts.com/ftopicp-432637.html#432637
here:
http://www.motorhomefacts.com/ftopicp-302446.html#302446
and here:
http://www.motorhomefacts.com/ftopicp-301759.html#301759

Nothing I've read so far in this thread makes me want to change my mind! 

Dave


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## aultymer (Jun 20, 2006)

Dave, at last a blast of sanity in this wondrous subject!! 

Frank, I believe it is not necessarily the watts involved but for some people the frequency can be "un-nerving"!! 
Glad you introduced the subject of functional earths. Now how do our electricians explain that away? If everything you plug in is effectively 2 pin with a dummy earth pin what difference does it make? 

While we are on the subject - If I am standing in our bathroom on an insulated floor I would expect to be safe from stray 250 volt potentials, until that is, I touch a carefully earthed water tap, which until the (regulation) earth cable was applied, was insulated by virtue of having a plastic supply pipe and had zero potential.


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## sallytrafic (Jan 17, 2006)

gromett said:


> I wouldn't recommend putting the earth to the chassis especially if going abroad. As the incoming earth from EHU may just be tied to Neutral and this can be volts different to real earth. This would put a potential difference between your vehicles chassis and the ground outside giving you nasty shocks when you get in and out.


On this point Karl why do both the 16th and 17th edition of the wiring regs specifically require you so to do?


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## thePassants (Feb 9, 2009)

Hello all, just thought I'd contribute...

Aside from the pro's and con's of various approaches and strategies:
From the relevant bit of BS7671 (Sect 721), I've managed to glean the following:

For 230v installations in Caravans (inc Motorcaravans)

- Minimum conductor size = 1.5mm2 (so not solely determined by current carrying capacity; and this is for the fixed wiring, ie to fixed sockets etc.) and must be flexible or stranded. _-so not 1.5 T&E!_

- Every low voltage socket-outlet (ie 230v) shall incorporate an earth contact.

- All protective conductors (ie earth) shall be incorporated in a multicore cable or in a conduit together with the live (ie L&N) conductors.

- Each installation (ie EHU & inverter) needs a double pole isolator, suitably placed for 'ready operation within the caravan'.

- Structural metallic parts which are accessible from within the caravan shall be connected to the main earthing terminal within the caravan (and therefore to the earth of circuits).

So, I guess a 'coke can' inverter (presumably with no connection to the earth pin) isn't a suitable origin for fixed wiring within the vehicle, although it may be suitable to supply an appliance directly.
But a built in inverter, supplying sockets etc. via fixed wiring would have to provide an 'earth' via the cpc of the cable & the earth contacts of the socket. Assuming an overcurrent device or RCD on the 230v side of the inverter, this needs to connect to 'the chassis' of the vehicle/inverter.

(As an aside: I'm not sure where the principle of discrimination, whereby the device nearest the fault should disconnect first can be applied where there is a non-time delayed 30mA RCD on an EHU supply, and also one in the caravan..? -but I guess that's a new topic!)


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## aultymer (Jun 20, 2006)

Hi, the Passants, 
Great to hear from someone who has access to the appropriate regs. 
I am a bit concerned about one section you quote, viz, 


> Every low voltage socket-outlet (ie 230v) shall incorporate an earth contact.


Presumably this earth contact, to be effective, must be connected to an 'earth' point. Having had to bury an old boiler plate in a sandy location in order to satisfy the electricity boards requirements on earthing I am wondering how this is achieved 'on the move' with an inverter supplying an appliance when driving. eg, kids using 'toys' in the back.


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## gromett (May 9, 2005)

Frank, My comments were aimed at people going abroad. In France they sometimes tie the earth to Neutral. As this is not always going to be at 0 volts it will create a potential between the vehicle and the physical ground.
If you are only ever going to be using proper English hookups wired 100% to to the Regs this will not be an issue. Do the regs cover vehicles that are going to be used in other countries? I am not disagreeing with you over what the IEE regs say I wouldn't dare disagree with you on that as you are still practising. 

AberdeenAngus. Sorry your last post just lost me. You are now into theoretical failure rates and statistics and back into unknowns. I am not qualified or knowledgeable on statistical analysis and will leave that to those with an interest in it. I stand by my statements regarding known failure and unknown failures.

Aultymer, The OP was on about a fixed installation. My complaint on this thread was about people telling him to not use an earth. This to me was seriously bad advise. The coke can inverters are a portable appliance in their own right. I am sure they will have some protection built in but if not they still fall under a different set of parameters to a fixed installation.
I could sit here an theorise on the two faults that would be required to put these devices into full failure mode that risks life but there wouldn't be any point, I would just be being argumentative.

Frank, on the functional earth question. I guess you are correct there. However I have had a belt off a supposedly double insulated plastic device in the past but again that was a rare failure mode of that device.

Dave, Nicely put, it is a complex subject. My complaint in this thread was about 2 posters saying without reservation that no earth is required as though it was fact. I have gotten sidetracked and off topic with Aberdeenangus for which I apologise.

The system I currently use is the same system as used by luxury yachts which are water based. If it's good enough for millionaires and mixes well with water it is good enough for me. Thankfully my electrical and electronic experience allows me to make judgements for my own use still.

My advice would be:
If you do not know for certain what you want to achieve, Get a professional to do it for you. At least that way if anything goes wrong at least you have someone to blame. If anyone tells you categorically that no earth is needed for any mobile system I would disregard that advice.

If you are doing it yourself. I wouldn't recommend permanently bonding the earth to the chassis if you are ever going to go abroad and will be using EHU's there. But you should get advise from a professional and not trust me as you don't know me from adam. However when not on EHU then your vehicles chassis should be bonded to the earth.

I would always recommend at a minimum having an RCD fitted to any 240V system. If it doesn't have a physical earth create one by bonding the earth to the neutral on the supply side of the RCD as stated in my previous thread. Even if you are just going straight from battery to inverter to a single socket. This is just an extra layer of protection.

Karl


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## aultymer (Jun 20, 2006)

> If you are doing it yourself. I wouldn't recommend permanently bonding the earth to the chassis if you are ever going to go abroad and will be using EHU's there. But you should get advise from a professional and not trust me as you don't know me from adam. However when not on EHU then your vehicles chassis should be bonded to the earth.


As a 'wallace' I have a natural affinity to 'Grommett' but your above comment highlights one of the problems with the present regulations and with trying to be helpful on open forumses or forii. 
If I go abroad I should not bond to the chassis but if I am not on hook up I must?
Does anyone supply a switch for this purpose?


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## thePassants (Feb 9, 2009)

aultymer said:


> While we are on the subject - If I am standing in our bathroom on an insulated floor I would expect to be safe from stray 250 volt potentials, until that is, I touch a carefully earthed water tap, which until the (regulation) earth cable was applied, was insulated by virtue of having a plastic supply pipe and had zero potential.


Earthing is frequently confused with 'equipotential bonding'; the purpose of which is to ensure that any Extraneous-conductive-part will be at substantially the same voltage (earth) as another one you might touch. This is so you don't get 'tingles' or worse by touching say, the tap and also the radiator (in a house). 
So a metal tap, unless part of a conductive system of pipework that is extensive does not require 'earthing' or bonding. Likewise metal sinks, metal door handles etc etc. However, the chassis, and the earth conductor of circuits, and obviously the supply; need to be 'bonded' to the Main Earthing Terminal.

A caravan has the same 'special' status as bathroom etc in a house, since the risk of electric shock is increased. That's why an RCD is a requirement for additional protection in such an installation.


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## aultymer (Jun 20, 2006)

> So, a metal tap unless part of conductive system of pipework that is fairly extensive does not require 'earthing' or bonding


Please tell that to the many qualified electricians out there who insist - if it is metal, it must be bonded. Tingles don't kill but an otherwise insulated and zero potential bit of metal can kill if 'bonded'. 
Tingles happen all the time if you are wearing the right (wrong) combination of clothes - they are usually only really painful when you touch a bonded component.


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## gromett (May 9, 2005)

aultymer said:


> If I go abroad I should not bond to the chassis but if I am not on hook up I must?
> Does anyone supply a switch for this purpose?


Don't take my word for this, check with a fully qualified person first who has experience of installing for vehicles that must work in other countries as well as to our own regs.

The Victron Multiplus has the relay for this built in. But a straight forward 240V relay would do the job just as well. The coil would go across the EHU input. Then the NC terminals of the relay would link chassis to socket earth. When the coil is energised by the incoming EHU it would open the NC points disconnecting the earth from the chassis.

Karl


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## gromett (May 9, 2005)

Sorry if my previous posts came across as either stroppy or know it all. I was quite angry that people were advising no earth in a motorhome without even finding out about the OP's actual installation. 

My installation is a really heavy duty one that involved ripping out some of the existing MH system and replacing it with my own. It was designed from the ground up and involved discussing the system with 3 Qualified people from different fields with me making the final decisions. Not one of those three people could give me a definitive answer. For example the Domestic/Industrial Electricians wasn't sure about connecting the earth to the chassis as it was also the 12V-. The Victron Specialist was telling me you should not connect the earth to the chassis when on shore supply but should be when off. The auto electrician was concerned about having 240V supplies in a vehicle full stop :lol: 

Anyway after finding out why each of them had concerns for a specific configuration I designed mine to cover out each of the concerns. for example. Not having the chassis earthed when on hookup was a concern because in some places there is no incoming earth. If the chassis of the vehicle was then connected to the incoming live it could give a shock. I protected against this by putting an additional RCD on the EHU input.

After lots of research and many circuit diagrams later I came up with a plan that all three 'experts' were comfortable with. It turned out to be a lot more simple than initial investigations indicated.

There are many details and questions left out of my above explanation so please don't try and pick it to pieces on the details. I wrote this to keep it simple.

Anyway, apologise if I came over badly in previous posts.

Karl


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## thePassants (Feb 9, 2009)

aultymer said:


> Presumably this earth contact, to be effective, must be connected to an 'earth' point. Having had to bury an old boiler plate in a sandy location in order to satisfy the electricity boards requirements on earthing I am wondering how this is achieved 'on the move' with an inverter supplying an appliance when driving. eg, kids using 'toys' in the back.


My understanding / interpretation of it all goes a little like this (for now!):
- The wiring regs BS7671 are for installations; fixed wiring of circuits etc.
- An inverter is a 'scource' of a supply at 230v.
- If you want to connect a supply to an installation (fixed wiring etc) in a caravan, and comply with BS7671, then you'll need an earth: an inverter can't magic one from no-where, I guess.
- Plugging an appliance into an inverter, powered off a 12v battery is not an installation. Using one to power installed circuits presumably is.
- ESQCR (google it; I'd never heard of it either) prohibit use of a combined Earth & Neutral system for caravans. (Implies a 'supplied Earth' system is required for hookup supply -and is presumably why generators ask for an earth electrode) I vaguely recall the instructions for an inverter I had on an old vehicle also saying one should be used...


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## aultymer (Jun 20, 2006)

> an inverter can't magic one from no-where, I guess.


This is the point I was hoping would emerge. 
If the inverter has no 'earth' connection then there is no point in creating one. 
The need for an 'earth' connection is a manufactured one from the UKs method of electrickery supply.
I would love someone to explain how a lethal potential can exist between a totally isolated inverter supply and 'earth'.
Oh, by the way, I am not going to hold the end of a wire to prove this one way or another.


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## thePassants (Feb 9, 2009)

aultymer said:


> > So, a metal tap unless part of conductive system of pipework that is fairly extensive does not require 'earthing' or bonding
> 
> 
> Please tell that to the many qualified electricians out there who insist - if it is metal, it must be bonded.


Indeed. I was told this practice dates from the 14th Edition (1966-1981) and is no longer a requirement.



aultymer said:


> Tingles don't kill but an otherwise insulated and zero potential bit of metal can kill if 'bonded'.


Really though; it's not the zero potential that's doing the killing here is it: It would be the faulty equipment or really, the non-compliant installation failing to protect the user from a fault or their own negligence. That's rather like blaming a stationary bus for smashing up your car; rather than your own faulty brakes or lack of concentration!

BS7671:2008 Sect 721.410.3.6 The protective measures of non-conducting location (Reg418.1) and earth-free local equipotential bonding (Reg418.2) are not permitted.

Rules is rules.
Re. Tingles: Perhaps nylon socks shouldn't be permitted either.

Ste P.


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## gromett (May 9, 2005)

Aultymer, this goes back to the double fault scenario.
Fault 1: 'IF' the chassis of the invertor was connected to the chassis of the vehicle
Fault 2: 'IF' an appliance developed a live fault.
Result: live potential between appliance and chassis = uncomfortable situation.

So you are relying on two faults not happening by not putting any protection in place. My argument is that you should not rely on two unknowns. 

I force the first fault (not really a fault) But as you are using an inverter you are not on EHU so you don't have an earth point. However you can tie the earth to the neutral which gives an alternate return path for the current. Providing this return point goes directly to neutral of the supply any fault condition will cause an inbalance in the RCD.

Two options here
1) rely on two faults not happening (how do you know if the first fault is not already there?)
2) Put the system into a situation where only one fault is possible and protect against it.

Again this is totally up to you, I prefer a known system.

Karl


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## gromett (May 9, 2005)

thePassants: regulations change over time fortunately. However these regulations are aimed at installations for use in the UK not motorhomes that will be used in a variety of circumstances and countries. I am not suggesting that we ignore the regs but we should not hold them as the absolute truth and ignore the realities of the situation.

If I get a tingle off something it means there is a fault somewhere in my book and I will correct it.

Karl


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## aultymer (Jun 20, 2006)

> Fault 1: 'IF' the chassis of the invertor was connected to the chassis of the vehicle
> Fault 2: 'IF' an appliance developed a live fault.
> Result: live potential between appliance and chassis = uncomfortable situation.
> So you are relying on two faults not happening by not putting any protection in place. My argument is that you should not rely on two unknowns.


My argument is that if the inverter is not connected to the chassis then your fault 2 can have no serious implications since no potential exists. Many inverters have plastic bodies so you would have to perversely connect their internal chassis to the vehicle.
We have reached an impasse here vis a vis UK shore supply, mainland supply and a vans inverter supply. This would appear to require a much more sophisticated control system than is offered on any production vans.


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## thePassants (Feb 9, 2009)

Karl,
I agree entirely; the IEE regs are guidance and not statute. So unless the Building Regulations definition of a 'dwelling' extends (!), or the MH is a place of work (please no), I'm sure they're not compulsory, but I gather most of the changes for the new edition were to do with European standardisation.

I was wondering though (as I'm new to MHs): do any manufacturers fit inverters powering the 230v circuits as standard? -if so what do they do? -if not, why?
Does anyone connect the chassis of their MH to ground with an earth electrode? -I saw a lorry the other day with power take-off sockets and it had a coil of wire and a copper stake clipped there next to them.
I suppose the real danger with an inverter is between its own terminals; until you reference it to something else.
Certainly sounds like you've thought it all through, and live to tell the tale!

Ste.


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## gromett (May 9, 2005)

Aultymer. You are correct if it is one of these coke can type ones then there is less risk. But the OP was on about a fixed installation, these type of inverters tend to have metal chassis and installed in lockers/garages?

I am using one of these, http://www.thepowerstore.co.uk/product.asp?ID=1379 with 880AH of battery bank. It is hard wired in with 2 RCD's and an MCB panel. Each battery is individually fused and has cuttoff switches and thermal protection. Not earthing a system like this is a little different from plugging a coke can into the cigar lighter socket 8O

Karl


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## JeanLuc (Jan 13, 2007)

Well!

I have followed this, sometimes quite heated, thread with interest and hope that I have learnt a lot from it. Thanks to all the contributors with much more knowledge than me. I have a very modest installation compared with the principal subjects of this conversation. I am one step up from the 'coke-can' inverter in that I have a Sterling 150W PS inverter which originally was supplied with a cigar lighter plug. However, having suffered from voltage drop when plugging it into the 12v socket in the (now empty) TV cupboard, I removed the cigar plug and wired it directly to the batteries via a switched relay on the +ve feed, protected with a 40A fuse. Then I used a 1.5 sq mm triple flex (an old PC power lead) to plug into the inverter output socket and wired this to a new 13A switched twin socket. All this is a stand-alone system not connected in any way to the van's 230V system.
But, there is no earth connection from the inverter body to the chassis or -ve side of the battery.

The point of this rambling account is that your learned debate on the subject of earthing prompted me to phone Sterling and speak to their technical support chap. Since I am only using small devices which are themselves double insulated (lap-top charger / powered PC speakers / camera chargers etc) and the 230v part of the system is a 'stand-alone' circuit, his advice was that earthing was not really necessary in my case.

I thought this information might be of use to others with small (plug-in) inverters.

Philip


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## gromett (May 9, 2005)

Hi Philip, That is another portable one. My comments re earthing relates to a fixed installation. However I have not actually heard of anyone suffering a fatal electric shock from an inverter. My preference for having a properly earthed system comes from being in the trade a number of years ago and wanting a "proper job". If your inverter is double insulated and all the appliances are it does reduce the risk dramatically. Sounds like you keep yours in an overhead cabinet or somewhere similar?

I just had another thought this morning however. The argument that the vehicle is on 4 rubber insulators only applies until you put the awning out. Thought about this while cleaning mine this morning..... I did a continuity check with my mega between the base of the leg and the van and there is an earth path there 8O Just need to think how that affects it all :lol: 

Karl


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## DABurleigh (May 9, 2005)

You could make a fortune Karl by designing a complex switch, driven by user-friendly menu software, to complicate the handbrake on, kettle on, arrival routine. I can see it now:

Are you in the UK? Y/N
Are you on EHU Y/N?
Do you have a genny? Y/N
Do you have an inverter? Y/N
Do you have an awning? Y/N

See, all earthing worries for Joe Motorhomer then disappear at a stroke! 

Dave


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## gromett (May 9, 2005)

Thanks Dave, My new business :wink: :lol: 

Karl


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## JeanLuc (Jan 13, 2007)

gromett said:


> If your inverter is double insulated and all the appliances are it does reduce the risk dramatically. Sounds like you keep yours in an overhead cabinet or somewhere similar?
> 
> Karl


Hi Karl,

I realised you were talking about a much more complex installation. Yes, my inverter is hidden away. I used to have it mounted in the old TV locker overhead, but that was where I was getting voltage drop as the standard Hymer 12v wiring to the socket in that cabinet was not heavy enough for the job. Now it is screwed to the floor under the L-shape settee where the battery box also sits (recessed below the floor). The wiring is all routed along the inside walls of the settee and only the twin 13A socket and relay activating switch are visible from the living area.

I am quite pleased with the result - I think it looks pretty professional anyway. I had thought of writing up my installation with some photos since many people seem to ask questions here about fitting inverters. They seem to cause a lot of misunderstanding. This would of course relate to a pretty simple installation only, but might be useful in the downloads section. However, I am not a qualified electrician - I just do a lot of research first and have always felt pretty comfortable dealing with basic electrics around the home. What do you (and other qualified experts) think? Would it be OK for me to do it?

Philip


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## thePassants (Feb 9, 2009)

Philip,
I'm sure a 'guide to...' would be useful for some. I reckon you'd need to fairly careful though about what you advise.
The installation you describe sounds fairly straight forward: basically a relay controlled by a switch on the ELV 12v system, and what could be regarded as an extension lead plugged into an inverter.
Quite possibly *not* a LV (230v) installation in a special location (specifically Caravans and Motor Caravans), for the purposes of BS7671; just an extension lead, plugged into a 12v appliance.
However;
If you take the view that a (or more) fixed double 230v socket, with _fixed_ wiring to a 230v scource *does* constitute an _installation_ for the purposes of BS7671, then it really ought to satisfy all the requirements of the standard; particularly Section 721 (Caravans...)

It's easy to take the view that this is all a bit pedantic, but consider the following scenario:
Fire in MH; Insurance claim (big one); Loss adjusters; DIY wiring additions found; Expert witness opinions as to compliance with relevant standards...

It soon begins to sound as defensible as non-standard tyres, chassis alterations, or home-made gas-lights.

I completely sympathise with the view that the 'Wiring Regulations' are not necessarily Gospel, or omnipotent. But:
Observation of them is widely held to amount to competence, and departure from them; under cross-examination would be asserted as incompetence. Now I doubt that as with Dwellings or Places of Work, failure to demonstrate competence could amount to a Criminal Offence, but it could certainly attract blame.
I reckon the best approach is try and find a way to claim compliance (jump a hoop), rather than attempt to dismiss what is a world-wide accepted Standard.

I realise this has all gotten a bit 'heavy', but in these litigious days it surely merits consideration!
Perhaps a carefully worded disclaimer should feature. ;o)

Ste. P.


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## aultymer (Jun 20, 2006)

> It's easy to take the view that this is all a bit pedantic, but consider the following scenario:
> Fire in MH; Insurance claim (big one); Loss adjusters; DIY wiring additions found


From the pictures I have seen of motorhome fires you would be pushed to find a wire far less a "wrongly" installed one!


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## AberdeenAngus (Jul 26, 2008)

gromett said:


> I just had another thought this morning however. The argument that the vehicle is on 4 rubber insulators only applies until you put the awning out. Thought about this while cleaning mine this morning..... I did a continuity check with my mega between the base of the leg and the van and there is an earth path there 8O Just need to think how that affects it all :lol:
> 
> Karl


It shouldn't affect things at all. Voltage does not have a natural wish to go down into the earth. Mains voltage tries to head to earth because the centre of the three phase generator (the neutral) is earthed at the power station. Hence 440v between phases and 240v between any phase and earth (neutral).
However in our own little private power station (i.e. the battery & inverter) nothing is earthed unless we make it so. The only potential is between the two inverter outputs, and there is actually no difference between the two outputs. We can call them Live and Neutral but which is called which, is arbitrary.


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