Grounding an inverter

[Seagreen]

Tried searching past threads, but the server is slower than molasses in january, so here goes:

I've just bought a handy little 230V 300/600W inverter from Aldi (on of their famous thursday specials) which has to be grounded. How do I do this (or do it with a generator) on a boat? Do I hang a cable over the side, or will a wire welded to a keelbolt/or stud through the immersed hull work?
Does this affect the electrolytic current round the hull vis-a-vis the fastenings, prop and anode? Its an old wood boat with a mix of mainly SBronze, copper and some iron fastenings, with a cast iron keel and forged iron keelbolts.

Confused.

 

[VicS]

No you create an "earth" system on board. That should include the main metal lumps and the 12volt negative and also anodes that have internal connections but not those protecting non ferrous fittings if you have any*.

In most cases the negative, engine and anodes will already be connected to each other so it is just a question of identifying a good point to connect the inverter earth to. The negative battery connection on the engine would be good.
The "neutral" side of the output from the inverter should be earthed at the inverter (it's not a neutral until it's earthed) but you should consult the manufacturers advice about that. It may already be earthed.

It practice that will mean that there is a connection to the water.

There is another thread running on the subject at present. You should read that but it has got rather confused/ confusing.

* If anodes are used to protect non ferrous fittings they should not be connected to the same system that is protecting ferrous fittings

 

[steve_cronin]

I would, and have,...

..also fitted a sintered copper grounding plate to ensure that a good earth contact is made. Ours is only 2" x 8" but because of it's "crinckled" surface treatment, it has an effective surface area of several square feet. Because of this it also makes a suberb earth for the Navtex and SSB receiver.

Steve cronin

 

[VicS]

Re: I would, and have,...

[ QUOTE ]
also fitted a sintered copper grounding plate to ensure that a good earth contact is made

[/ QUOTE ] I don't think its necessary for electrical safety on board with an inverter or a generator for that matter. In Seagreen's case with a wooden hull and the collection of metals he has I think it would be advisable not to fit a copper plate. In fact I think he should ensure that there is no electrical connection between his non ferrous through hulls and the ferrous bits. the effect of electrolysis products on the wood is always at the back of my mind!

In my previous post I should have said that a generator should be treated in the same way as far as earthing is concerned (You don't normally expect to be considering both at the same time!)

 

[roly_voya]

Re: I would, and have,...

Think about what the earths do?

12v ground is in fact not an earth at all but simply the neg terminal on the battery. The 12v system does not care about the voltage to ground as long as it gets 12v btween pos and neg. 12v systems do not have a risk of electricution so don't need a safety earth.
Anodes (corrosion ground)- Although conected to the water this is not an 'earth' but in effect one plate of a dry cell battery, its job is to supply a tiny current that errodes away the anode and plates all the other underwwater metal. It does this because if it happens the other way round you are erroding your fittings. The only reason to 'ground' the 12v neg to the anode is that most alternators and engine sensors are not isolated so will conect the 12v neg to ground via the prop shaft if it is not isolated via the coupling and therefore the dc circit the ant-corrosion circit become combined. If the engine bock is not electrically conected to the shaft you dont need to connect the block to the anode but you do still need to protect the shaft outboard of the issolation point either via the hull anode or a shaft anode
240v - Compleatly different animal this is a SAFETY GROUND for a potentially lethal voltage. In the event of a fault the 240v earth takes the full fault current safely to ground which not only avoids it going through people but also makes sure there is enough current flow to trip the breakers/fuses. Without a proper earth a fault can lead to all the cases for your 240v gear staying live untill the do find a ground - possibly through you with fatal results. It is essential that this earth piont is directly to the water. all the cassings on 240v gear MUST be grounded including the case on any mains battery charger and inverter. The nutral line on the inverter is internally connected to the earth should not be grounded. The keel can be used as one ground provided it is external, metal and not isolated by paint which can be an issue particularly with epoxy coatings
Radio grounds. Thease are effectively part of the radio arial and essential for SSB etc to work (though not vhf) they should only take radio frequency and attaching anything else to them can cause interference.

So there are up to 4 seperate 'grounds' doing diferent jobs, why would thy be connected?

The 12v ground (ie the neg batt teminal) might be connected to the anode depending on the configeration of the boat, particularly engine system. If you are not sure McDuff will happily give adice if you email a description and have good recomendations on there site for common layouts

Radio ground - always seperate from averything else

240v. The only 'safety' ground. Ther are only 2 configurations allowed under European (ISO) standards and it depends on the shorepower conection. If the shorepower lead goes immediatly to an RCD then the 240v ground should be seperate from all others. If the shorepower lead does not go to an RCD i'e' it connects directly to any equipment such as a battery charger then the 12v neg MUST be connected to the 240v earth. IT IS VITAL that this connection is done right though. When crounding the 12v system it should go to a seperate stud on the ground plate. NEVER connect the 240v earth directly to the neg battery terminal or connect both earths to the same stud because if you do and it fractures due to corrosion or comes off then in the event of a fault the current will be grounded through the 12v system and all you 12v stuff plus possibly the engine block will go 240v live - not a nice thought!

Be careful, in the event of an accident whoever installed the system can be held liable so if in any doubt consult a marine electrition - for a fee they may be happy to check a system you have installed.

Finally don't think that any of this is less important because you have a small inverter, even the smallest ones made can produce thousands of time mre current than it take to kill you - its the votage that matters not the power available!

 

[steve_cronin]

For the reasons you have identified.....

...I am sometimes dismayed as to why people don't realise the need for equi-potential bonding of all socket plates, sinks and waste pipes in domestic kitchen installations. I have spent the last two days restoring this in a flat we recently bought. I was also horrified that after my mother in law had a new bathroom fitted by "professionals" (pre Code P) that they had ripped all the bonding straps off and that they just lay there under her bath, not connected.

Thanks for pointing out the need for seperate connections to the ground plate. Ours has these. However the SSb shares with the battery charger as we don't often use it whilst connected up to shorepower so interference isn't a big issue.

Steve cronin

 

[bluedragon]

[ QUOTE ]

* If anodes are used to protect non ferrous fittings they should not be connected to the same system that is protecting ferrous fittings

[/ QUOTE ]

Haven't heard this before. I know it's not quite the topic being discussed here, but where can I find out more info? My hull anode is internally bonded to seacocks, shaft / prop, rudder fittings & engine. These are a mix of bronze and iron and possibly some S/S. In fact the prop shaft is bronze and attaches of course to the (iron) engine. So do I have a potential problem??

 

[lw395]

An RCCB is a VERY good idea whenever 230V is near water!
What are you going to run from the inverter? Many items are double insulated with no earth anyway. Its a difficult scenario because most boats will have lots of unbonded metalwork, the regulations are not really conceived with yacht installations in mind, and the anode dimension adds further doubt. Earthing will only kill the power if the earth loop can carry enough amps to blow the fuse. An RCCB will switch off when 30milliamps go astray.
What does the BSS for inland say?
Hope that helps,
Chris

 

[Seagreen]

Re: I would, and have,...

Wow. Unleashed a hornets nest. I can see I'm going to have to give the electrical system a complete shake up over the winter, not just rewire the panel!

There's a lot to digest here, and the suggestion I get a qualified marine electrician may help, though apart from the engine Alternator, the system is a simple 12v one.

As for the safety grounding of the 240V system, I presume this also applies to any 240V sockets put in as part of the shore power set up? I've a double socket (basically a permanent extension lead set up) into which a proper waterproof (dunno the standard spec) plug and lead combination fits. Does this also need to be earthed, or as it is merely a spur, can it stand alone? Should I put an RCCB in at the socket as well?

 

[VicS]

[ QUOTE ]
Haven't heard this before

[/ QUOTE ]MGDuff say in the Fitting instructions "Do not bond the same anode to ferrous and non-ferrous metals"

My interpretation of that is that non-ferrous and ferrous items should not be connected to the same system of anodes.

However in the MAIB report into the flooding of the fishing vessel Random Harvest one of the recommendations was: "Disconnecting all through-hull fittings from the vessel’s cathodic protection system"

Remember that to afford protection an anode must the reasonably close to the item(s) it is to protect and be "able to see it". Unless all the items you mention are close together they may not all be protected by one just anode. Bronze ( and DZR brass) should not normally need protection, hence the validity of the recommendation in the MAIB report.

Stainless steel has to be considered as though it were mild steel as far as cathodic protection is concerned as the normal protection, by means of a oxide film, is no longer effective once cathodic protection is applied.

You can take the engine out of the equation because the only way a directly cooled engine can be protected is by internal anodes (which it may not in fact have!). Bonding the engine or gearbox to the anode(s) is often done as a means of connecting the shaft and propeller to the system but the more effective method is with brushes running on the shaft (I think that is covered somewhere on the MGDuff website).

 

[Seagreen]

[ QUOTE ]
What are you going to run from the inverter?

[/ QUOTE ]
Substantially, nothing larger than a laptop, or maybe small DVD/TV for short periods. Anything that needs more power- a smaller sander- has a small petrol generator to do that, should it need it.

If this is the case, do I need to bother with an earth at all? I'm an electrical dunce.

 

[bluedragon]

Thanks. I'll have a read and maybe speak with MG Duff. I have disconnected some of the bronze connections anyway (Blakes sea cock in the heads for example). As nearly all the metal is bronze anyway (except for the transom-hung rudder pin which is S/S) I'm wondering if I even need an anode? The engine does have one. Worth a re-think this winter.