Caravan Earthing

Submitted: Friday, May 27, 2005 at 14:42
ThreadID: 23356 Views:10291 Replies:8 FollowUps:5
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Can anyone explain how the 240v system in a caravan is earthed? Is it to the chassis?

I have just bought an inverter and need to earth it on the AC side. I can run an earth cable from the earth connector on the inverter to a metal rod that is hammered into the ground, or can I connect up to an earth pin in a 240v plug and plug it into an available 240v socket on the basis it is earthed to the caravan's chassis?

How have others done this?
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Reply By: macka2 - Friday, May 27, 2005 at 16:44

Friday, May 27, 2005 at 16:44
I suggest you check with manufacturer as earth(s) are often in the walls too!
AnswerID: 113198

Reply By: Sparkie C - Friday, May 27, 2005 at 18:38

Friday, May 27, 2005 at 18:38
Why do you need to earth the earth pin on the invertor? Most invertors are set up with a system that does not require or relate to earth , they are suitable for a single appliance use.
It is not wise to connect to an indipendant earth stake as you cannot determine it real resistance and simply the electrode may become live if there is a fault.
Refer to the Electrical Safety Office in your state and get a qualified electrician who specialises invertors to advise you .
Please be very carefull as there have been several fatalities due to people connecting invertors wrongly!
AnswerID: 113219

Reply By: DerekH - Friday, May 27, 2005 at 19:11

Friday, May 27, 2005 at 19:11
Sorry for the long post, but here are some details of the inverter, its instructions and the set up I was hoping for.

The inverter is a Powertech MI-5106, 400W with 1200W surge.

I am a dunce when it comes to how electricity works, hence my request for some advice. Here is some stuff from the instructions which have half a page on the "grounding connection". Hopefully, it might help to explain how this particular inverter, which I bought from Jaycar, works - I will call them tomorrow to see what they advise.

The inverter has an earth terminal and the instructions deal with several different situations for earthing. For example: "in a land based installation, the earth terminal should be connected to metal earthing stake driven into the ground to a depth of 1.2m or more. If the battery system powering the inverter does not have a connection to ground one of the battery terminals (commonly the negative terminal) should also be connected to the earthing stake."

Then: "in vehicles where the inverter is wired directly to the battery, the earth terminal is simply connected to the vehicle chassis."

And: " if the inverter is to be used in a vehicle on a temporary basis and will be powered via the cigarette lighter socket, the earth terminal should be connected via a short link to either the negative or positive DC input terminal of the inverter."

Then again: "when using the inverter outside of the vehicle, use an earthing stake as above."

I was advised that I could use a powerstrip on the AC side of the inverter to connect a TV, VCR and antenna amplifier. I have a 12v socket inside the caravan where I was planning to plug in the inverter.
AnswerID: 113227

Follow Up By: drivesafe - Friday, May 27, 2005 at 20:53

Friday, May 27, 2005 at 20:53
Hi DerekH, I have the powertech inverters as well.

I think you will find that the earth connection, via the wing nut on the back of the inverter, is actually intended to reduce power hum, but as Sparkie C said, go and check with the relevant authorities or get in touch with Jaycar.

Cheers
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FollowupID: 369403

Reply By: Woobla (WA) - Friday, May 27, 2005 at 20:52

Friday, May 27, 2005 at 20:52
Hi Derek,
I am an electrician and have just read the speel on my digitor inverter and hope I can give you a little advice.
Iam assuming the vehicle is negative earth on the 12volt side. Things change dangerously if the vehicle wiring system is positive earth!
The metal case of the inverter is connected internally to the earth of the inverter power outlet. The 240 volt earthing system of caravans is also bonded to the frame and all metal of the van.
Quite simply, if you intend using your inverter in a van or trailer, make sure you physically fix the inverter to the metal of the van or trailer.
240 volts can kill and you should always disconnect the 12 volt power before working on anything connected to the inverter.
Probably sounds a bit simple but you dont get second chances with electricity too often.
Jeff
AnswerID: 113252

Follow Up By: kev.h - Friday, May 27, 2005 at 21:34

Friday, May 27, 2005 at 21:34
Hi Woobla
would i be right to say the earthing of the caravan chassis etc is through the earth pin on the power cord plugged in from the mains supply
(therefor you may not have an earth circuit i no power supply) so maybe with the inverter you would need an earth stake i always use one when the generator is plugged into my camper
Cheers Kev
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FollowupID: 369417

Follow Up By: DerekH - Saturday, May 28, 2005 at 10:17

Saturday, May 28, 2005 at 10:17
kev.h's point is what I had in mind. In my original post, I said I had thought of wiring the earth connector on the inverter to the earth pin on a 240v plug and simply plugging it in to a socket in the van, on the basis that I would then be connected to the van's earthing system. But I was concerned that with no power supply, the grounding would go "nowhere".

Also, what defines an earth stake?
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FollowupID: 369447

Reply By: Woobla (WA) - Saturday, May 28, 2005 at 10:32

Saturday, May 28, 2005 at 10:32
Hi Kev,
If you fix your inverter, so that it is solidly connected to the metal frame of your van, you will not need to have an earth stake.
The earthing thing is to ensure there is no difference in potential between the metal surfaces where you are likely to come in contact with a live wire.
ie If there was a fault in your microwave and it shorted to the earth of the micro cabinet and your microwave was not earthed and you touched the frame of your van that was earthed, you would get a boot, if, however, the van and the microwave were both the same potential (both earthed to the same point, through the earth cables of the appliance), this would cause a short and the fault would blow a fuse etc.
This may seem a tad confusing but realistically if you tried bashing an earth stake in every time you went in to a caravan park, sooner or later you would bash your stake through a power conduit and end up with singed eyebrows!
If you are using the inverter in your van, conected to a 12v power supply that is negative earth..(most vehicles) then just make sure you fix the inverter to the metal frame of the van. if I have not made this clear enough, and I may not have, I suggest you take your van, your inverter and a slab of beer to your nearest electrician.
Regards,
Jeff
AnswerID: 113301

Follow Up By: kev.h - Saturday, May 28, 2005 at 18:01

Saturday, May 28, 2005 at 18:01
Thanks Wobbla
I was never sure so i erred on the safe side with the generator. What you say makes sence with the inverter earther to the van
Kev
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FollowupID: 369492

Reply By: DerekH - Saturday, May 28, 2005 at 10:49

Saturday, May 28, 2005 at 10:49
I just called Jaycar. The guy said I did not need to earth this inverter and that I would only have a problem if one of the devices connected had been wired up incorrectly.

This conflicts with the advice posted so far and with the instructions which say the inverter must be grounded.

Will the earth pin on one of the van's 240v sockets connect to the van's earthing system? Can I use it rather than fixing the inverter directly to the van's metal chassis/frame?
AnswerID: 113302

Follow Up By: Mad Dog (Australia) - Saturday, May 28, 2005 at 11:53

Saturday, May 28, 2005 at 11:53
Confusing isn't it Derek.

From what I've read it doesn't matter too much one way or the other if the inverter is earthed or not except in the case of non double insulated inverters where there may be some potential for the 240 volt side to leak back to the 12 volt side if a fault should develop. In this case if the insulation should break down and the invertor is earthed to the chassis then someone could get fried. There is no need to be banging in earth stakes.

Have a read of this article

http://www.aroundoz.com/diy_archive/inverter.htm

Where one manufacturer of non isolated inverters states that the above scenario is impossible with his inverters.

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FollowupID: 369455

Reply By: drivesafe - Saturday, May 28, 2005 at 18:27

Saturday, May 28, 2005 at 18:27
Folks, the original suggestion by Sparkie C is the one you should go with if you are not absolutely sure you know what you are doing.

Tampering with the the earth in a camper trailer, caravan or motor home could easily result it serious harm being caused to yourself or to someone that may at sometime have to work on your vehicle.

There are stringent laws pertaining to the wiring in such vehicles and if you ever intend to use a caravan park power supply, then your vehicle will not only have to comply with the rules but if you have wired the earth incorrectly, you may not be able to use the park power as they all, by law have to have safety switching on the power outlets and as such, an incorrectly wired vehicle may cause the power to continually trip.

Cheers
AnswerID: 113366

Reply By: DerekH - Sunday, May 29, 2005 at 11:33

Sunday, May 29, 2005 at 11:33
Thank you all for your feedback. In the end, we decided our need for an inverter wasn't warranted anyway - we don't need the TV, which was teh only reason we were considering it - so I will take it back to Jaycar.

We can then enjoy the peace of the bush uninterrupted, except for the bugger next door with the inverter, the TV, the boom box, etc....
AnswerID: 113448

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