# Inverters & getting down to earth



## shingi (Apr 18, 2008)

One for sparkies I think?

Been reading with great interest many of your informative posts on the fitting of 12v to 230v inverters whilst making provisional plans to fit one myself sometime. One question has come to mind which hopefully someone (& I know they will !) answer.

In a 230v EHU situation as we know, earth or grounding is provided from an external source. When EHU is not available and an inverter is in use to provide 230v from the 12v leisure batteries, what gives any appliance plugged into the inverter it's earthing should a fault occur?


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## VanFlair (Nov 21, 2009)

I think the answer will be that you ground the inverter to the chassis and make sure the power from the inverter is supplied via a RCD trip. I say think as I am no expert so I will watch with interest.

Martin


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## listerdiesel (Aug 3, 2012)

There is no earth protection as such.

What we describe as an 'earth' is in fact the centre point of a 3-phase source that is connected to both the ground point of our homes, usually the metal pipes used for water, and the neutral connections in our fuseboards and sockets.

You don't have any of that infrastructure in your motorhomes or on a portable generator, which is why you don't have RCD's on these appliances.

You have the option of leaving the output fully floating, which I prefer, or you can ground one pole of the output to the vehicle chassis, which I think is a waste of time.

If it is fully floating, you won't get a shock off either conductor should you inadvertently touch it while the inverter is running, while if you ground one side of the output, you are far more likely to get a shock as the other lead is now referenced to all earthed parts of the vehicle.

Obviously if you grab one output lead in each hand, we will be reading your obitury here! 8O 

Peter

Edit: There is nothing wrong with doing as Martin suggests, but personally I wouldn't bother. It is a 2-wire AC source that is fully floating and best left that way.


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## shingi (Apr 18, 2008)

Thanks to both Martin and particularly Peter for the very straightforward explanation to my query which is very much appreciated.

Could I be a little bit cheeky and ask another question, still about inverters, but on a slightly different tack? 

Assuming an inverter is correctly connected to the 12v leisure batteries, which will already be directly (or indirectly say through relays or the like) connected to the m/homes existing internal systems, is there any likelihood that the strong "draw" on the batteries from the inverter would have any adverse effect on the already present components within the vans electrics? I ask this because modern MH electrics with controls, printed circuits etc, relays and the like can sometimes be susceptible to, shall I say, "sudden unexpected demands" from the likes of an inverter being imposed into the system? Any thoughts would be interesting.


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## shingi (Apr 18, 2008)

Oh, and I forgot to say Peter......................

No, I wont be holding the red in the left hand and black in the right !!


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## listerdiesel (Aug 3, 2012)

shingi said:


> Oh, and I forgot to say Peter......................
> 
> No, I wont be holding the red in the left hand and black in the right !!


Should be Blue and Brown really.....  

Regarding the effect of turning the inverter on, as long as the batteries are in a decent state of charge, the transient voltage dip wouldn't do any harm, especially on a smallish inverter.

What 'would' cause an issue is a partially flat battery and a big inverter being switched on, then you may get a forced restart on things that need a good 12V supply to operate.

Many diesel cars get problems in the winter through their batteries going below the required support voltage for the ECU's and other electronics, causes mayhem.

Peter


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## VanFlair (Nov 21, 2009)

I had faith in Peter coming along and keeping us right.

Martin


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## rayrecrok (Nov 21, 2008)

Hi.

On my 3000 watt Ring inverter there is an earth screw/bolt that I lead a wire to the existing earth on the chassis..

I have one of those testers that are like a 13 amp plug you just plug in any 13amp socket to test for earth's etc, with various lights that come on inside the tester body to show faults and it always shows no earth on the van.

ray.


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## shingi (Apr 18, 2008)

Thanks Peter, you've answered both my little queries in style, and now armed with all the many posts that already exist on the subject of inverters on the superb MHFs pages, I can now plan ahead in confidence.

Ray: Yes I've seen those earthing screw/bolts on the casing of some inverters which I didn't mention previously as I didn't want to complicate things, but thanks anyway for your input.

P.S. I wasn't going to mention this previously because I didn't want to embarrass myself, but is all this work and expense really necessary only so that wifey can use her 230v hair dryer when wild camping? :roll 

Happy motorhoming, Regards Mike


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## teemyob (Nov 22, 2005)

listerdiesel said:


> shingi said:
> 
> 
> > Oh, and I forgot to say Peter......................
> ...


And on our German Motorhome. It is Brown and Black, with brown being earth. Despite knowing this and going over it time and time again, I fried and Inverter with no reverse polarity protection when I connected it up.

TM


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## listerdiesel (Aug 3, 2012)

The earthing stud on the casing isn't normally connected to the output of the inverter, so technically would have no effect electrically. You'd need a strange fault to get 230V onto it, involving a multi-component and insulation failure.

In my experience, the semiconductors fail long before that becomes likely.

If it WAS connected to one leg of the output it would contravene the Low Voltage Directive, which is why the outputs are usually completely free floating.

Peter


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## Jezport (Jun 19, 2008)

I wouldn't bother for a hairdryer as they are too power hungry.


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