Inverter earth confused

Submitted: Tuesday, Feb 13, 2007 at 23:52
ThreadID: 42287 Views:14467 Replies:13 FollowUps:13
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I have a 300w inverter but lost the instructions . From memory it said if the unit is connected to the car battery don't have to worry about earthing it as the negative terminal on the car battery is earthed to the chassis.

It has an earth screw on the metal cover of the inverter and mentioned something about connecting that to stake and ramming it into the ground if it isn't connected to a battery with a negative earth. The inverter will be mostly used in a 6 by 4 trailer . If the inverter is in contact with the trailer body does this count as an earth? I don't fancy zapping myself maybe I just put it away all too confusing

cheers
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Reply By: Member - Pedro the One (QLD) - Wednesday, Feb 14, 2007 at 00:11

Wednesday, Feb 14, 2007 at 00:11
Hi Pixiemops ................

Not really my field, but isn't the trailer insulated from EARTH by the tyres and jockey wheel ??? Unless it is still connected to the vehicle .................

Agree, this 12v stuff is very confusing for us lay people !!
AnswerID: 221574

Follow Up By: Richard Kovac - Wednesday, Feb 14, 2007 at 00:15

Wednesday, Feb 14, 2007 at 00:15
smarter people will answer

Tar Richard
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Follow Up By: pixiemops - Wednesday, Feb 14, 2007 at 00:16

Wednesday, Feb 14, 2007 at 00:16
Good point if it was connected to vehicle then I suppose it would be earthed .Didn't think that buying this inverter was going to give me such a headache. Thanks Pedro
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Follow Up By: Gerhardp1 - Wednesday, Feb 14, 2007 at 18:52

Wednesday, Feb 14, 2007 at 18:52
NEVER rely on the towbar to provide an earth. Mostly it does, but don't rely on it.

A separate wire via trailer plug and preferably anderson plug is needed.
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Reply By: Richard Kovac - Wednesday, Feb 14, 2007 at 00:13

Wednesday, Feb 14, 2007 at 00:13
Hi pixiemops

This may get the right reply

But Earth means earth, if your car trailer has rubber tires then it's not earthed' But for better protection hook the wire from the earth terminal to any metal part which is attached to the negitive battery terminal.

Richard

You cannot die ("maybe") from 12 volts

Please do not try this at home
AnswerID: 221575

Reply By: Mainey (WA) - Wednesday, Feb 14, 2007 at 02:00

Wednesday, Feb 14, 2007 at 02:00
First off... yes you can die from 12v :-(

Run the Pos+ cable to the Pos+ battery terminal.
Run the Neg- cable to the Neg- battery terminal, NOT the body.

Only use secured fittings.

Remember you are now 'playing' with 240 VOLTS
AnswerID: 221583

Reply By: Mike Harding - Wednesday, Feb 14, 2007 at 06:23

Wednesday, Feb 14, 2007 at 06:23
For an inverter used in a camping situation there is no need to earth it. It is arguable that doing so increases the risk of electrical shock.

Mike Harding
AnswerID: 221585

Reply By: Derek from Affordable Batteries & Radiators - Wednesday, Feb 14, 2007 at 08:14

Wednesday, Feb 14, 2007 at 08:14
Hi Pixiemops

Don't be scared of 12V unless there is high amps. DC current can be dangerous when the amps are increased or like already mentioned it is turned into 240v.

1 or 2 automotive batteries is safe to work with.

There is no need to earth the unit but it is 240V so same rules apply as at home.

No water, rain and handle with care.

Regards

Derek.
AnswerID: 221593

Follow Up By: pixiemops - Wednesday, Feb 14, 2007 at 08:24

Wednesday, Feb 14, 2007 at 08:24
Thanks alot everyone for the advice . I might watch a bit of telly camping afterall.
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Reply By: Member - Woodsy - Wednesday, Feb 14, 2007 at 08:33

Wednesday, Feb 14, 2007 at 08:33
Hu pixiemops

I don't want to delve into the possible safety aspects of your query but I had an inverter that I used in a cabin cruiser to run a 240V stereo. There was a lot of static in the radio reception.

I was advised to connect the earth to an earth point. Hey Presto! Static dissapeared.

Anyhow, that's my contribution.
Happy 4 wheeling

Woodsy

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AnswerID: 221599

Reply By: Willem - Wednesday, Feb 14, 2007 at 09:41

Wednesday, Feb 14, 2007 at 09:41
My inverter came with one positive wire and two negative earthing wires. One to the negative battery terminal and one earthed to metal in vehicle body frame.
AnswerID: 221607

Reply By: PhilZD30Patrol - Wednesday, Feb 14, 2007 at 09:58

Wednesday, Feb 14, 2007 at 09:58
Hi

Don't shoot the messenger but some of you won't like what you read below.

The purpose of the inverter is to provide 240 volt AC energy. This is the same as you get out of a power point at home. 240 Volt AC is the same and can kill no matter how it is produced!

Australian Standard AS3000 Series describes how earthing of electrical installations is to be carried out. As far as I am aware, compliance to AS 3000 is a legal requirement in all Australian States and Territories. In certainly is the case in NSW, Queensland and the A.C.T. Failure to comply can be a criminal offence.

All installations and servicing of 240 volt AC electrical equipment and appliances must be carried out and tested by a licensed A Grade Electrical Fitter or Mechanic (Electrician).

A normal domestic safety switch typically disconnects the supply in 40 milliseconds (0.04 s) for a leakage of 30 milliamps because it has been found that currents higher than 30 milliamps passing through human beings can kill.

Don't forget that very young children's soft moist skin is highly conductive and they are could easily touch the side of a caravan while standing bare footed on moist ground.

So the safe thing to do with an inverter is to drive an earth stake into the ground and connect it with a suitable cable to the earth terminal on your inverter because when using a 240 volt AV appliance supplied by an inverter it is important to ensure that the electrical potential of the accessible metal casing of the appliance and the inverter is zero.

Simply put, a car, metal caravan or trailer can be classed as an appliance if 240 AC is distributed and used within the vehicle. There is an Australian Standard for 240 volt AC installations in a mobile vehicle, caravan and trailer.

If in doubt go and discuss this with your Electrical installation Inspector at your local Electricity Supply Organisation.

Cheers
Phil
Licensed A Grade Electrical Fitter and Mechanic (Electrician)
AnswerID: 221609

Follow Up By: Mike Harding - Wednesday, Feb 14, 2007 at 17:20

Wednesday, Feb 14, 2007 at 17:20
Hi Phil

I don't believe an inverter powered from a battery in a camping situation is classified as an "electrical installation" under AS3000 - just think what safeguards would be needed for the 25kV "installation" which powers your spark plugs!

With the domestic electricity supply it is essential to earth most appliances because earth and neutral are bonded together therefore if an appliance were not earthed and a fault occurred which caused it's casing to become "live" then current would flow through anyone who touched it via the earth to neutral and they would not like that :) As you will probably know one can happily hang on to the active line providing one is not touching earth and no shock will result. Working on live equipment is regularly done in this manner - up to many thousands of volts.

With an inverter (or a portable generator) it's neutral pole is not bonded to earth (ie the planet) and, therefore, you can happily stand in wet grass with bare feet holding the 240V active line from the inverter (gen) and not receive a shock (ensure the gen. frame isn't touching the wet grass too). However should you grasp the neutral in the other hand you will. By earthing a portable installation I would argue one actually increases the risk of electrocution by increasing the probability of someone coming into contact with both poles (and, probably, a couple of Hungarians too! :)

Mike Harding
Who has a few qualifications in the electrical area too.
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Follow Up By: Bonz (Vic) - Wednesday, Feb 14, 2007 at 18:13

Wednesday, Feb 14, 2007 at 18:13
I quote: "The principal application of this standard is to electrical installations in all types of premises and land used by electricity consumers"

That means bulidings etc connected to the electricity grid hence the term consumers.

It does not mean shacks out in the bush running off generators

It does not mean camper trailers running off generators or inverters

Check the definitions in your copy of AS/NZS 3000:2000 for definitions of premises and electrical installations and appliances. I am sure you'll see it doesnt mean a car or CT off an inverter.

There are regs for Caravans though as I recall.
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Follow Up By: Mike Harding - Wednesday, Feb 14, 2007 at 18:47

Wednesday, Feb 14, 2007 at 18:47
>There are regs for Caravans though as I recall.

And that's quite sensible because caravans often hook up to the domestic grid.

Mike Harding
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Reply By: PhilZD30Patrol - Wednesday, Feb 14, 2007 at 18:01

Wednesday, Feb 14, 2007 at 18:01
Hello Mike

The majority of scientists now believe death is permanent.

I realise I have opened up the proverbial "can of worms".

I do know what I am talking about as I was once employed working with Electrical Inspectors.

I wrote my response because there is a potential danger, it may only be 10,000,000 to 1, of receiving a severe electrical shock. About as much chance of winning lotto but then someone must win lotto sometimes.

I can assure you that if there was an accident, the police would call in the OH&S authorities, ( Workcover or Worksafe or whatever it is called in the State or Territory) and the Electrical Installation Inspectors would become involved.

The AS 3000 series has many standards on electrical subjects. Have a look at the ones about earthing and earth bonding of mobile and stationary generators and other electrical equipment and the standard on electrical installations in mobile homes and caravans.

Cheers
Phil
AnswerID: 221715

Follow Up By: Mike Harding - Wednesday, Feb 14, 2007 at 18:33

Wednesday, Feb 14, 2007 at 18:33
Hi Phil

Will you please explain to me why connecting a portable generator or inverter to earth (ie the planet) makes the installation more safe?

Mike Harding
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Reply By: avro - Wednesday, Feb 14, 2007 at 21:41

Wednesday, Feb 14, 2007 at 21:41
I am very definitely with Mike on this one. Earthing an inverter or generator either to ground or metal chassis of vehicle just gives you a far greater chance of a person becoming the circuit in the event of a fault in an appliance attached to the device. As Mike explained you have to touch both an active and an inactive point on AC to form a circuit. Highly unlikely with an internal fault in an appliance that you would be able to do that, but if its "earthed" then highly likely that you could form a circuit (from "earth" to appliance.

Another issue is that a large number of inverters do not have an electrically isolated 12 volt section. I understand that this IS an OH&S issue. To my knowledge the Jaycar ones are isolated, dont know of any others.

This is my view only, I do not have any formal qualifications in this area, but plenty of practical exposure.

Regards avro
AnswerID: 221776

Follow Up By: PhilZD30Patrol - Thursday, Feb 15, 2007 at 09:03

Thursday, Feb 15, 2007 at 09:03
Hi Mike

The main purpose of my response to this forum is to address the original question about the use and earthing of an inverter.

The main issue is HANDLE WITH CARE because 240 volts AC is potentially very dangerous no matter from where it is sourced.

It takes a very low number of milliamps to cause a serious accident.

If in any doubt at all get professional advice. Good luck for anyone who is unfortunate enough to be in a position of trying to justify their actions that did not comply with the Australian Electrical Standards.

As far as your questions;

1. A possible dangerous situation could be a faulty inverter e.g. the active shorting to the metal case, and an appliance with loose or broken earth and neutral wires and poor insulation resistance to the metal case (e.g. as often found in old drills and Mix Masters). There are many different scenarios.

2. Earthing the inverter to a earth stake may prevent some potentially dangerous situations but cannot make the use of an inverter 100% safe in every situation. Like a home installation, it is obvious that the MEN system does not eliminate every potential electrical accident; however, it assists in limiting some dangerous situations.

I guess that there are some situations where the MEN System may potentially create a dangerous situation.

3. I have assumed that the earth pin and neutral in a common inverter are linked and connecting it to an earth stake makes it a simple MEN system. The advantages of MEN systems have been debated and are proven since beginning of time, electrically speaking of course.

I once did maintenance work in a Power Station where some GPOs were not earthed in special situations to isolate them from the system. It all can get very complex.

Cheers
Phil
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Reply By: pixiemops - Thursday, Feb 15, 2007 at 09:34

Thursday, Feb 15, 2007 at 09:34
Thnaks alot guys for all your responses. Yesterday I phoned about 5 different auto-electricians and from them got the following suggestions.

1. All we do here is wire the earth to the negative terminal of the battery. Another auto sparky said that is a no no.

2. Another suggested just wire the earth to a metal part of your car. Someone else said that is not right as the earth in 12v ie the car is very different to the earth in 240v .

3. Another suggested use the earth stake and a shop that specialises in inverter sales says he has never heard of anyone having to earth an inverter full stop and didnt think it necessary.

So now I am very confused even the auto electricians seem not to give a definite answer. I think I will use a stake . It will be a long way from the inverter and trailer up near the tow bar. Maybe there needs to be some very clear guidlines for people like me and the auto sparkies as well on this one.

thanks
AnswerID: 221841

Reply By: PhilZD30Patrol - Thursday, Feb 15, 2007 at 14:00

Thursday, Feb 15, 2007 at 14:00
Hi Pixiemops

Follow up from my other responses, I have just found the instructions to my inverter which confirm that the inverter must be earthed. I quote "WARNING: BEFORE USING THIS INVERTER YOU MUST PROVIDE A GROUND CONNECTION TO THE INVERTER".

They then describe how it is done, by connecting a heavy duty queen-insulated wire to the wing nut connection on the inverter which is connected to the earth terminal of the outlet.

The heavy duty queen-insulated wire should be connected to a metal earthing stake driven into the ground to a depth of 1.2 metres or more.

hope this helps
Cheers
Phil
AnswerID: 221880

Follow Up By: PhilZD30Patrol - Thursday, Feb 15, 2007 at 14:06

Thursday, Feb 15, 2007 at 14:06
Hi Again Pisiemops

Auto electricians do not have the qualifications or experience to provide professional advice about 240 volt AC.

As recommended earlier, if in doubt ask the Installation Inspectors of your local electricity supply authority.

As my boss told me when I was an apprentice electrician, "Scientists agree death is very permanent"

After all you don't get a Pastry Cook to cook a Chinese Banquet, even though they are both in the cooking trades.

Cheers
Phil
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Follow Up By: Member - Beatit (QLD) - Thursday, Feb 15, 2007 at 14:39

Thursday, Feb 15, 2007 at 14:39
G'day Phil,

Appreciated your educated input and don't mean to make light of good practices. But are you saying that with any inverter used in a van one would be required to drive a 1.2 m stake in the ground to make it safe/compliant?

I'm not in the game so have no expertise to make a challenge but I've been to places where driving a tent peg into the ground was an engineering feat let alone pulling the bugger out later!

I am imagining a lot of lost/left stakes. Also I will need to start working out to have any chance to get a stake down that far.

Can't see anyone doing this but I might be wrong. So this is then just added to the growing list of law breaking on the margin such as being overladen, speeding and other indiscretions that will bite you when something goes wrong. I am surprised that no one has raised the matter of it effecting ones insurance etc

Kind regards
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Follow Up By: PhilZD30Patrol - Thursday, Feb 15, 2007 at 15:07

Thursday, Feb 15, 2007 at 15:07
Hi Beatit

The short answer is stuffed if I know.

You question has raised the age old problem of how does one apply bureaucratic laws, standards and regulations to the many different circumstances that are encountered.

One way is to grind a sharp point on the stake and pour a lot of water around the soil where the stake is to be driven. But, currently in most places in Oz the soil is harder than my mother in laws heart and a sharp stake and heaps of water, if any can be found won't make any difference.

Drive the stake in as far as you can and use the inverter with care. The main thing I think is important is to keep the inverter and appliances out of reach of children and away from moisture and metal.

Another safety item could be to purchase a 3 core lead with a safety switch, (RCD or ELB depending on how old you are and what school you went to). Safety switches are worth their weight in gold and should be used everywhere at all times.

Hope this helps
Regards
Phil
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Follow Up By: pixiemops - Thursday, Feb 15, 2007 at 17:09

Thursday, Feb 15, 2007 at 17:09
Interesting

Yes this inverter seems alot of trouble.I was wondering how on earth I would bang in a stake that far as I recall my instructions did mention something like that. I certainly see few people out when Im camping banging metal stakes into the ground. But if its what you have to do then I guess you must do it. More trouble than its worth . Glad I wont be dependant on this bloody thing was just for a few luxuries like tv .

I guess when you can't earth it with a stake when you are camping on rocks like you say keep it away from metal moisture and use with care.

Thanks.
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Reply By: Mike Harding - Thursday, Feb 15, 2007 at 18:08

Thursday, Feb 15, 2007 at 18:08
Hi Phil

>It takes a very low number of milliamps to cause a serious accident.

It’s actually about power rather than current; which is why you can touch a 12V battery with a couple of thousand amps capability or a coil ignition system with 25kV but a very low current capability without harm… however don’t try touching a 25kV, 2000A power supply! :)

>1. A possible dangerous situation could be a faulty inverter
>e.g. the active shorting to the metal case

That would cause one of the inverter fuses to rupture or destroy the output stages of the inverter, it would not cause any part of the installation to become live at 240V relative to the planet earth.

>and an appliance with loose or broken earth and neutral wires
>and poor insulation resistance to the metal case

If the appliance has a broken earth it doesn’t matter what you do! If it has a broken neutral then it simply won’t work. If it’s leaky from the appliance active to the appliance case then providing you _don’t_ earth the inverter you won’t receive a shock because there is no way for that leakage current to return to the neutral pole. This is exactly the situation in which earthing the inverter raises the danger level.

>Like a home installation

That’s the thing Phil – an inverter (gen) in a camping situation is nothing like a domestic installation because it’s not bonded to earth and does not need to be.

>I have just found the instructions to my inverter which confirm
>that the inverter must be earthed. I quote "WARNING: BEFORE
>USING THIS INVERTER YOU MUST PROVIDE A GROUND
>CONNECTION TO THE INVERTER".

They say that as a legal getout in case the inverter is (as they often are) used in conjunction with a solar system and the domestic mains, in that case there is good reason to earth the inverter or standby generator – in a camping, or stand-alone, situation there is not.

Phil: do you agree that with a non-earthed inverter or gen one could stand on the ground and touch the active connection and not receive a shock?

Mike Harding

mike_harding@fastmail.fm
AnswerID: 221928

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