Inverter help

[FNQCairns]

I think FNQ should scan & post the directions so we can decipher them for him. (HINT)

Ok paraphrasing a little but leaving nothing important out- stationary land based, earth terminal connected to metal earthing stake to a depth of 1.2m. if the battery powering the inverter has no connection to ground then one of the battery terminals (commonly negative) should also be connected to the earthing stake.

In a vehicle when the inverter is directly wired to the battery the earth terminal is simply connected to the vehicle. If temporary ie cigarette lighter plug, the chassis earth terminal should be connected via a short link to either the -ve DC terminal of the inverter.

cheers fnq

[frank100]

Very interesting !
Are'nt ships supplied deliberately not earthed ? ie the only way to get a boot is to grab both supply cables. Also I thought that with such a system protection is usually provided so that if either side of the supply is eathed in some way the protection isolates the supply or provides some sort of warning ie alarm buzzer or warning lamps.
The earthing of one side of a dc supply on metal ships / boats could lead to some interesting electrolytic reactions (eating a hole in the hull etc).

FNQ if you have to use 240v gear & an inverter, I would suggest you keep the inverter dry but ventilated, keeps DC connections tight & make sure the DC supply cable is more than sufficient to handle the current & has fuse / breaker (or both) protection and lastly keep the 240v cables(rated for at least 600v peak) short & well protected (mechanically that is).
Ca'nt see the point of bonding the chassis earth terminal to -ve battery though ( but instructions should be mostly followed or so I'm told ).

Frank

[oldboot]

I would not trust the directions as far as i could comfortably spit a medium sized mullet....( who was that cartoonist?)

The instructions almost certainly are not written with an understanding of australian "electrical philosophy".

In some counties I believe they still do not have a seperate earth connection.
many countries certainly do not subscribe to the MEN earthing system.

So you are going camping..... are you going to drive a 4 foot earth stake..... what are you going to do when you have finished......have you ever tried to pull up a 4 foot tent peg...... come to think of it have you ever driven a 4 foot tent peg.

In some areas driving an earth stake ( remember this is a tent peg that comes up to your chin) into the ground is a "major commitment".
Even then can the average consumer assess the earth resistance as being satisfactory.......try getting an earth on a sand hill.

Why is there a need to bond the negative of the DC side to an earth?.... there should be 3KV isolation between the 240V and DC side of the inverter.

I have no problem with an inverter sitting on a wooden table, plugged directly into an double insulated appliance and connected to a battery sitting on the floor....as long as it is all secure and dry.
Now before anybody has a go at this one..... think carefully.......what can possibly occur that bonding to the greater mass of earth would improve.
Even if you now substitute a metal cased & earth connected appliance.... show me a possible fault that bonding would improve.

We must understand that the earth reference is supplied by the supply device... the functioning of the earthing system within the appliance remains...as the 240V supply is with reference to the earth of the supply device.

everything changes though when you introduce a metal structure such as a table or a vehicle or an installed wiring system.

Now think a bit more..... we have a motorhome.... with an inverter "correctly installed" and earth bonded to the metal structure...... do we drive an earth stake every time we stop............it is precisely the same issue.

How about a plane....

Told you as long as the airconditioning is cold and the sandwedges last.

cheers

[TheRealAndy]

It is illegal for you to connect you genset/inverter earth to an earth stake unless you are a qualified electrician. All you can do is plug stuff in


Whilst none of this is legal to do without a qulaified electrician, if your genset/inverter has an RCD, see photo on how it is wired, or how it should be wired. If fitted to a boat with shore power the isolation switch should also remove the earth neutral bond when connected to shore. Note I have left out fuses/breakers, but the should be fitted to the genset/inverter after the RCD, but obviously before the GPO.

Me personally,a ground stake is waste of time as it does nothing. An earth stake is only needed for utility power. Not sure if there are any regulations around dealing with the issue but I am fairly certain there wasn't when I was a practicing sparky. IF there was I never knew about them.

[TheRealAndy]

Well as far as gensets are concerned AS/NZS 3000:2000 The rules say this:

2.5.6.3.1 Connection of generating set bonding system. Where a generating set supplies an electrical installation that incorporates an earthing system, the bonding system of the generating set (see Clause 2.5.6.1) shall be earthed by connection to the earthing system of the electrical installation.

Connection to earth shall not be made by means of a separate earth electrode.

The generating set bonding system is required to be connected to the electrical installation earthing system in this situation but not via a separate earth electrode.

Further more:

4.2.3 Earth electrode
The connection of a generating set bonding system to the general mass of the earth through an
earth electrode is not required or recommended.”


Now I dont have a later copy of the standards, but looking as SA website suggest that they ammended the regulations circa 2004 regarding inverters. Perhaps someone who has the regs can take a look. I also see references to AS/NZS 3012.

So there you have it, dont bond your earth to an earth stake.

Further more, I made a mistake in my last post which I will correct, the breakers are fitted after the RCD. The isolation switch is fitted before the RCD.

[oldboot]

G'day Andy... would you like lemonade or ginger ale with your sandwedge

some of my points exactly..... but with references to back it up...

cheers

[Twisted_Pair]

G’day FNQ,

As stated previously by oldboot your inverter installation is an Isolated Supply or to quote from the new current which came into force 1/6/08 AS/NZS 3000:2007 Clause 7.4 now falls under Electrical Separation.

There are 3 types of Electrical Separation supplies (clause 7.4.2):
a) an isolating transformer
b) a generator (output separated from frame)
c) an isolated inverter to AS/NZS 4763 (that’s you)

There are 2 types of connection.

1) Single item of electrical equipment (clause 7.4.5) states:
“where a separated circuit supplies a single item of electrical equipment, any exposed conductive parts of the electrical equipment shall not be connected to the exposed conductive parts of any other circuit, including other separated circuits or earth”.

2) Multiple items of electrical equipment (clause 7.4.6) states:
“Where a separated circuit supplies more than one item of electrical equipment, the following shall apply:
a) Any exposed conductive parts of the separated circuit shall be connected together by an insulated equipotential bonding conductor that is not connected to –
i) earth; or
ii) a protective earthing conductor or exposed conductive parts of another circuit, including another separated circuit; or
iii) any extraneous conductive parts.

b) The designated protective earthing contact of any socket-outlet installed on the separated circuit shall be connected to the equipotential bonding conductor.
c) The designated protective earthing conductor in any supply cable or flexible cord to electrical equipment (other than Class II double insulated equipment) connected to the separated circuit shall be connected to the equipotential bonding conductor.
d) Exposed conductive parts of the source of supply that are earthed, shall not be simultaneously accessible with any exposed conductive part of the separated circuit.
e) A protective device shall operate to disconnect the separated circuit automatically in the event of two faults resulting in exposed conductive parts being connected to live parts of different polarity. If the protective device is a circuit breaker, the protective device shall open in all unearthed conductors substantially together.”

Andy, those clause numbers from AS3000:2000 you quote are not in any of my standards including 1991, 1986, 1981 or 1976. Can you check your AS source as to your references above (I’d really like to know which one). The earthing section in AS3000 for the last 30 years has always been section 5.

I agree with oldboot and therealandy, but we need to keep up with the current standards if quoting them to the general public.

My aircon is set to 22degC .

Regards, T_P

[TheRealAndy]

Well spotted twisted_pair, my apologies the reference is to AS3010:2005. My confusion lies as 3010 makes some references to 3000. A misquote indeed.

Do you have access to the 2007 version of AS3000? I did read on the standards australia website that they wer talking of appending 3000 or 3012 with some details on inverters.

[oldboot]

I think we should move this meeting to Twisted pair's place......if you don't like the cold bring a jumper

seriously.....I need to buy a new coppy 0f AS3000.......they had to make some ammendments for inverters and the like because they are all over the place now.

I think the important thing to understand is that the "earth" is supplied by the source of supply.
This nailing things to the greater mass of earth realy derives from the electrical distribution system...... more or less because the power station is nailed to the ground.... everything connected to is has to be..... but that is the MEN earthing system and many electricians don't fully grasp that philosophy..... they just install to the regs.

the bizare concept to grasp is that the neutral is connected to the earth in our system....at specific points.
some countries their 220V supply has what amounts to 2 actives

If this meeting goes on uch longer we'll have to call out for pizza.

cheers

[Twisted_Pair]

No worries Andy,
Yes I have AS3000:2007 as I'm still plugging along in my business.

The new bible hasn't much on inverters, but makes mention in 4.12.1 & 2 that an inverter is also called a Semiconductor Power Converter and for selection and installation of such devices the AS 60146 series should be used for guidance (which I don't have).
Section 7.3 Electricty Generation Systems now also mentions inverters under 7.3.1 (b) Stand-alone power systems & Section 7.4 as mentioned earlier.

Regards,
T_P

[PADDLES]

i stand corrected oldboot and tp. you're absolutely right, i just had a read of the wiring rules and there it is in 7.4. i still don't understand it fully though, what is the purpose of the "earth" on a seperated circuit? is it purely to create a return path for the protection to operate? a bit confused now, i've always relied on bonding to minimise/eliminate touch potentials and now here we could potentially have a "live" external part of a device that is at a higher potential than what you are standing on. is this system relying purely on there being no return path to the source to keep you safe?

edit: just quizzed the boss and he was just as confused as me but came up with the same assumption that it must get treated as a floating supply and as long as there is no return path to the source you are safe (do you really trust it), i learn new stuff every day! oh yeah, aircon is about 23 here, bit sweaty outside just before but it's all nice now i'm back in here.

[oldboot]

prior to the advent of ELCB... it was considered that the primary reason for an earth connection and an earthed metal case was to provide a return path for the functioning of protective devices such as fuses and breakers... elcb just makes it work better and faster.
Remember the toaster luke.... use the toaster.
They still teach this and it will be in the exam.

the only time a metal case could become "live" is if the protective device did not function......
now in a the clasic "toaster example"...if the eliment became dislodged and contacted the case part way along, sufficeint to provide an operational load and not a short circuit, the earthed case diverted the flow of electricity providing a low impedance path back to neutral. and a measure of protection from shock....this is and always was a secondary function of the earth...important though it may be.
This situation will not occur with ELCB

the earth's function is to provide an auxliuary path back to the neutral of the power supply, primarily for the functioning of protecive devices.

now consider your portable supply device generates its voltage on its active in relation to its neutral which is bonded to its "earth" connection.... nothing has changed.... the earthed case of the toaster is still providing an auxliuary low impedance path back to neutral......so in both the long and short circuit faults the operation remains the same.

Ah this might be the missing bit...the earth is "bonded" to the neutral at source of supply.....inside the inverter.

However the whole system is independent of the greater mass of earth....unless the power supply device is bonded ( intentionaly or not) to greater mass of earth the person can not get a shock between the case and greater mass of earth.

Just like those isolation transformers we used to use in the 60's & 70's before ELCB

the only complication is when we introduce other unbonded metal parts into the equasion such as a metal table......if the earth conductor in the toaster is faulty and a secondary fault occurs allowing 240V contact to the metal case we now have a metal case that is live in relation to the inverters case. ( our "earth")....the inverters case is sitting on the metal table with poor contact & therfore poor earth resistance...the toaster has rubber feet......the protection circuits do not operate.
"Test person" touches case of toaster and table....." electrical incident " occurs.

similar with jamming the cord in the door of a vehicle where an unbonded inverter is operating.

There are many many issues that complicate the matter, when we start bonding things on a braod scale, like in our distribution system.....then we get earth potential rise, step voltages, significant earth inpedances, earth loops.....none of these situations will occur within a simple uninstalled system.

Where we have a portable supply device and a single appliance... it is the closest thing we will ever find to the textbook "toaster example".

the problem I think with "electricians" is that the day to day job has so many complexities....and sneaky regulations waiting to bite you on the bum....that when something very simple comes along.....they can not believe it is that simple..........

For those who don't get the joke... the toaster is used as the example in many texts and some standards to illustrate metal case earthing concepts.
Always go back to the toaster.

cheers

[Twisted_Pair]

Always go back to the toaster

Toasted sangers, now your talking!

T_P