Using Inverters In Vehicles

[Old.Tony]

Well, guys, here's an interesting topic. It raised its head because in our new van, I wanted to run the refrigerator off an inverted 240V supply so that the thermostat worked, and I was told that this was illegal in NSW.

So I got to researching and I can't find the legislation that disallows the use of an inverter in a towed vehicle that is in motion. If anyone knows where this regulation is I'd really appreciated being pointed in its direction.

What I HAVE found is a LOT of people doing it, and a LOT of people doing it the WRONG way.

The big trouble with inverted power supplies is the lack of residual current protection. If you have TWO earthed devices plugged into a single inverter and each device has a fault or a connection that brings part of its body into contact with that power, AND a human touches the two devices, they are electrocuted.

The problem exists (this is my understanding which may be slightly inaccurate but from what I've been reading it's close) because the earth point of one device feeds back to the inverter and out to the second device. This allows a circuit to develop where, given the faults, a full 240V can be developed across the two devices. A human bridging that gap dies. If some flammable or ignitable material bridges the gap there is a risk of fire.

Put plainly and simply, it is dangerous to put two EARTHED 240V devices on the same inverter.

This DOES mean that it is quite safe to use a SINGLE device on the inverter, and from what I can tell, you can do that while on the move. A corollary would be that you could use two unearthed devices, or an earthed device and an unearthed device if you wish.

Looking at the power requirements of the new van, I'm going to take up someone's offer of cheap heavy gauge cable. I've gotta do some thread searching to find who it was (the old grey matter has lost this info in the fog) so when I find ya, expect a pm. I'm going to run fresh cables from engine bay to tow hitch, then put some really heavy connectors on and run new cable down through the chassis of the new van into the cupboard near the fridge.

Naturally, if there is a law that says I can't have ONE device on an inverter while moving, I won't do it.

So, can anyone shed some light on this legislation?

 

[justdrinkbeer]

That was probably me Tony, the 10mm stuff, I just ordered 100m of it for a job.

I'll do some head scratching re. the inverter situation too, from what you've said it shouldn't be a problem as the two devices would be earthed back to the same point, with any fault current heading back to the Neutral from there, so Potential Difference would be zero, an issue would come if you had an appliance that was supposed to be earthed but wasn't, that developed a fault and you touched that appliance, and one that WAS earthed at the same time, hence completing the circuit.
Like I say, i'll do some head scratching but thats how it seems to me.

Rich

 

[Old.Tony]

Sounds like the cable I'm after. I'm going to need *counts fingers* 7 metres for the car and maybe 7 or 8 metres for the van. I might make it 20m of black and 20m of red so I've got enough to do the job. Where can I get it?

 

[Krankin]

So, can anyone shed some light on this legislation?

.

This is the bible

http://infostore.saiglobal.com/store2/Details.aspx?productID=1085701


or you can do it the way of it works, who cares if its not right or safe...

problem with inverters in vehicles is they're not grounded to the earth ground mass under your feet like mains power is.
Anyway, if you install as per AS/NZS 3001:2008 you're doing it to the best standard of the time.



have a squizz here also...have not read it all...seems a good read anyway..

http://caravanersforum.com/viewtopic.php?f=2&t=8782&start=20



.

 

[BravoBrad]

G'day Tony.

Id like to read the article about running two devices off an inverter being dangourous.(if you still have a link) The reason I say that, is we run multiple devices of inverters all day long (24/7all year). They are designed to do it. Even a cheapo large capacity inverter will have two sockets on it.

The only recomendations I can think of are as follows.
Make sure you earth the inverter to its frame, so that if the power earth gets displaced, you still have protective earth from the 2nd earth.
Don't overload the inverter, buy bigger than you need.
If it is running off your car Battery, turn the inverter off when you start the car, then restart the inverter.
You can also install a RCD off the inverter, and plug your devices into that (same for Generators)

 

[Krankin]

G'day Tony.

Id like to read the article about running two devices off an inverter being dangourous.(if you still have a link) The reason I say that, is we run multiple devices of inverters all day long (24/7all year). They are designed to do it. Even a cheapo large capacity inverter will have two sockets on it.

its not about overloading the inverter by running more than one device.

 

[Old.Tony]

I found some opinions on that Caravanner's forum but referred to the problem originally by the supplier of the caravan, who in every other respect gave me good and reliable information. I actually dealt with someone that didn't come across like a used car salesperson, which I must say made me feel very different to other caravan sales yards. It was just this one solitary point that stuck and my investigation led me to a bunch of opinions, hence my request for the legislation.

I've got some reading to do, it seems. I think the most likely path I'm going to follow will be this: heavy 12V cable coming in to a chassis-connected inverter employing an RCD, but only powering a single device. If I want a second device, I will get a second inverter - looks to me like that is the safest and probably the best path in reliability. I will need to make my fancy relay box up again, but hey that's all part of the fun!

 

[Krankin]

I found some opinions on that Caravanner's forum but referred to the problem originally by the supplier of the caravan, who in every other respect gave me good and reliable information. I actually dealt with someone that didn't come across like a used car salesperson, which I must say made me feel very different to other caravan sales yards. It was just this one solitary point that stuck and my investigation led me to a bunch of opinions, hence my request for the legislation.

I've got some reading to do, it seems. I think the most likely path I'm going to follow will be this: heavy 12V cable coming in to a chassis-connected inverter employing an RCD, but only powering a single device. If I want a second device, I will get a second inverter - looks to me like that is the safest and probably the best path in reliability. I will need to make my fancy relay box up again, but hey that's all part of the fun!

Personally I'd get a copy of the standard an go by that, then at least you know your covered,
keep in mind too that any 240vac 'fixed' wiring needs to be 'by law' done by a licenced elec.
Anyway run everything via an RCD box and if you dont overload the inverters capacity youll be ok
also make sure all your 240v gear is up to scratch and safe.

I dont have a copy of that standard, though i will try and get one,
and,
if anyone here knows someone that is going to uni and some other institutions, they are able to download ANY Aust Standard for only the cost of the paper its printed on...ie:FREE.

Oh, Tony, dont take that carvan forum thread as gospel, I had abit more of a read, the only right way is by the current standard atm.

 

[BravoBrad]

Whilst any item can be faulty, and cause harm, the only way I can think that an inverter would become a issue is if it was an old one that wasnt an isolation transformer. Providing you dont buy from an overseas suplier you should be save, as I think you can only buy isolation inverters in Australia these days (excluding ebay traders that could be flogging anything)

The thing to remember is how to set up the RCD. I would think that using the caravans earth is the best, as you are in the caravan, leaning on the caravan etc etc if your in using the powered device. I would be very hesitant to go down the path of attempting earth stakes etc.
a) its a job for a licenced sparky from memory
b) you could potentially kill yourself putting in the stake
c) If you are in the van, its not going to work to its full potential anyway.

Other things to remember

a) RCD is not a cure all (buts its as close as you will get)
b) if a device is faulty it will still bite you, doesnt matter if its at home of in the van.

The only reason I can think of for it being illegal to use an inverter whilst traveling is that in the event of an accident, emergency services could be exposed to a vehicle thats live(240v) that they wernt expecting.

 

[KraftyPg]

The only reason I can think of for it being illegal to use an inverter whilst traveling is that in the event of an accident, emergency services could be exposed to a vehicle thats live(240v) that they wernt expecting.

In the words of Mythbusters "plausible". It used to be (and maybe still is) illegal to run gas powered fridges while moving and the LPG stickers on car number plates are there for similar reasons, so it's conceivable for 240V appliances to be treated similarly

 

[Scottar]

Tony,

The issue may be not two devices but two different earths when the van is plugged in at a caravan park etc. A potential could well exist between the two if there is no connection. I know that with boats it is not uncommon to have some equipment running off inverters while the rest is off either shore power or a genset. Might be worth talking to a marine sparky to see if they use a connection to tie the earths together or other precautions??
The problem could also be related to the fact that the van is not truly earthed until it is plugged in to a grid connected supply (assuming the chassis has been connected to the earth of the input) as it is insulated by the tires. I would however attack your research from the electrical end rather than the caravan end. From my brief experience with a couple of vans the people that wire them don't always know what they are doing.

 

[Krankin]

Theres no need for speculation.....

AS/NZS 3001:2008 has the answers.......

 

[jjohn]

The only reason I can think of for it being illegal to use an inverter whilst traveling is that in the event of an accident, emergency services could be exposed to a vehicle thats live(240v) that they wernt expecting.[/QUOTE]

Very good point, Thanks!

 

[Old.Tony]

My goal - and it's how I have this running in my current caravan - is to have the inverter power down when the 12V source is removed (either turning off the ignition or unplugging the trailer). I know a couple of electricians, I'll see if I can get my hands on AS/NZS 3001:2008 and I'll read up on it.

Thanks for the standards info, that was what I was looking for!

Now, to get the document and make sure that everything complies.

 

[Peter ST_R]

Inverters are isolation step-up transformers which means there is no reference to earth, generators in most cases are the same. Normal transformers that power your house have their nuetral connected to the mass of earth throughout the electrical network and at each main switchboard which means the ground form part of the electrical circuit.

There is no problem with only one faulty earthed appliance on an inverter as the current has no return path to the source (inverter) through the ground. Put a second faulty earthed appliance onto that transformer than two seperate voltage potentials could exist between the two appliances and if you make contact between the two current will pass through you and you will get an electric shock.

If you run all your appliances through an RCD (must be Residual Current Device not power board with overload protection) than any earth fault will trip the RCD, isolating the power supply to the appliances. I am not sure about the legal side of this but I know the theory is good.

 

[justdrinkbeer]

Inverters are isolation step-up transformers which means there is no reference to earth, generators in most cases are the same. Normal transformers that power your house have their nuetral connected to the mass of earth throughout the electrical network and at each main switchboard which means the ground form part of the electrical circuit.

There is no problem with only one faulty earthed appliance on an inverter as the current has no return path to the source (inverter) through the ground. Put a second faulty earthed appliance onto that transformer than two seperate voltage potentials could exist between the two appliances and if you make contact between the two current will pass through you and you will get an electric shock.

If you run all your appliances through an RCD (must be Residual Current Device not power board with overload protection) than any earth fault will trip the RCD, isolating the power supply to the appliances. I am not sure about the legal side of this but I know the theory is good.

Then you'd need to create an MEN point at the transformer and earth everything and put the RCD upstream of that or you would never get an imbalance

 

[Krankin]

my rcd outlet box works straight out of the inverter in my workvan with no mods,
thats not to say though that it complies with 3001:2008.

 

[Old.Tony]

Looks like I'm reworking my power system in the current van anyway, and will be introducing this "newfangled" system in the new van as well. I'd like it to comply with the standards, and an RCD is going to be involved for safety.

It appears that RCDs work by detecting a difference in the current flow in the active and neutral lines - the general rule of thumb is that in a properly working system without any faults, the amount of current in the active and neutral lines is equal. When a fault develops, or a human is exposed to the power drawing some of that current away, the balance is lost and the RCD trips.

Okay, now that I know how one of these suckers works, I can see how you could use it to protect the output of an inverter - just put it in series with the output. Would connecting the case of the inverter (its earth point) to the chassis be sufficient to become a relative earth point? Would that reference provide a means of allowing the RCD to trip properly?

 

[Krankin]

will the inverter ouput/sockets in the van be seperate to the 240v installation that is powered by the c/park site supply?

 

[Old.Tony]

Yes and no. What I've wired up in the van at the moment is a relay whose coil is energised by the incoming 12V supply from the car, the relay is NC with the mains power driving a power point, and when energised the inverter (also powered by that incoming 12V) supplies power to the power point, from which a battery charger (C-Tek) charges the battery.

In other words, there's no actual connection between the outputs, only a relationship based on the state of the input from the tow vehicle.