Csail
N/A
I have an 1800w Sterling inverter on board, should it be earthed and if so where?
Inverter
- Thread starter Csail
- Start date
fluffc
Well-Known Member
What you need to do is to go to the supermarket and buy a Can of Worms....
There has been much debate on the forums about 240v earthing, mainly pertaining to generators. A general concensus doesn't exist, although many forumites can express their views with a good degree of logic.
Personally, I don't bother with specific earthing for the inverter.
You could, if you were feeling generous, connect the earth to the 12V Negative supply. Assuming that the major metalwork of your boat is also connected to the negative supply then you have created an equipotential zone.
There has been much debate on the forums about 240v earthing, mainly pertaining to generators. A general concensus doesn't exist, although many forumites can express their views with a good degree of logic.
Personally, I don't bother with specific earthing for the inverter.
You could, if you were feeling generous, connect the earth to the 12V Negative supply. Assuming that the major metalwork of your boat is also connected to the negative supply then you have created an equipotential zone.
steve_cronin
N/A
Yes, the case has an earth connection on it which needs connecting to a hull mounted, sintered bronze earth plate which can be obtained from most on-line chandlers. Just connecting it to a metal skin fitting is not wise for a variety of reasons like galvanic action, insufficient surface area and personal safety.
Steve Cronin
Steve Cronin
fireball
Well-Known Member
Does the casing have an earth connection? If not (like ours hasn't) then no. I haven't tested if the Earth connection is connected to the battery 0ve.
Csail
N/A
The inverter has got a bolt with earth written on it that's why i ask.
fireball
Well-Known Member
Then they are expecting it to be earthed!
The purpose of the Earth connection is to provide an alternative route for the current should the appliance fail. There are then earth leakage sensors that cut out the circuit hopefully before the appliance has a chance to electrocute you.
The purpose of the Earth connection is to provide an alternative route for the current should the appliance fail. There are then earth leakage sensors that cut out the circuit hopefully before the appliance has a chance to electrocute you.
steve_cronin
N/A
[ QUOTE ]
You could, if you were feeling generous, connect the earth to the 12V Negative supply. Assuming that the major metalwork of your boat is also connected to the negative supply then you have created an equipotential zone.
[/ QUOTE ]
What you propose could turn out to be shocking advice.
Consider the reason(s0 why the inverter needs to be earthed.
1. To ensure safety if an internal fault makes the case of the inverter live.
2. To run to earth the results of any "live case" or "live chassis2 of any device connected to it.
What you propose would render all the "negative" sides of any devices in your "equipotential" system live too. In the case of a boat with a saildrive, that would also include the engine as this is not connected to earth via the gearbox and drive-shaft as in a conventional drive. Although, I suppose, whislt it's running, there Is a path through the cooling water but that cannot be relied upon to be 100% safe..
A proper earth shoe or plate is the ONLY satisfactory answer.
Steve cronin
You could, if you were feeling generous, connect the earth to the 12V Negative supply. Assuming that the major metalwork of your boat is also connected to the negative supply then you have created an equipotential zone.
[/ QUOTE ]
What you propose could turn out to be shocking advice.
Consider the reason(s0 why the inverter needs to be earthed.
1. To ensure safety if an internal fault makes the case of the inverter live.
2. To run to earth the results of any "live case" or "live chassis2 of any device connected to it.
What you propose would render all the "negative" sides of any devices in your "equipotential" system live too. In the case of a boat with a saildrive, that would also include the engine as this is not connected to earth via the gearbox and drive-shaft as in a conventional drive. Although, I suppose, whislt it's running, there Is a path through the cooling water but that cannot be relied upon to be 100% safe..
A proper earth shoe or plate is the ONLY satisfactory answer.
Steve cronin
rogerthebodger
Well-Known Member
I have been reading with interest all the posts on earthing and do have a problem with some of the comments made.
If I remember my power distribution theory the supply side i.e. the substation has the neutral side of the transformed power connected to earth and it is this connection that will allow the return path if an appliance earthed case becomes connected to the line side of the supply, and with a RCCD between the supply and the appliance will trip as there is now a differance in the current flow in the line and neutral side of the circuit
Now this would mean that the case of the inverter or generator is also connected to the neutral so if the line side of the inverter had a fault that connected it to the case this would not trip the RCCD as it is not in circuit but may blow the main fuse inside the inverter if there is one.
As to connecting this earth / neutral to an outside plate under water I am not sure of the function of this in an enclosed system with inverter / generator.
If the boat has shore power this would give an additional earth path if the earth wire in the lead to the shore power commection became faulty of the galvanic isolator became faulty
This earth / neutral connection now makes it important to get the phase connection of the shore power correct at it could put live power on the wrong side of the power switch and where as normally the live does through the switch first then the element / motor / etc second this is reversed. The down side is that if a live fault to earth occures the RCCD would trip when the fault occured where as with the phase connection correct this would only happen when the appliance was switch on.
I know this is very technical but would like comments from some of the electrical engineers around
If I remember my power distribution theory the supply side i.e. the substation has the neutral side of the transformed power connected to earth and it is this connection that will allow the return path if an appliance earthed case becomes connected to the line side of the supply, and with a RCCD between the supply and the appliance will trip as there is now a differance in the current flow in the line and neutral side of the circuit
Now this would mean that the case of the inverter or generator is also connected to the neutral so if the line side of the inverter had a fault that connected it to the case this would not trip the RCCD as it is not in circuit but may blow the main fuse inside the inverter if there is one.
As to connecting this earth / neutral to an outside plate under water I am not sure of the function of this in an enclosed system with inverter / generator.
If the boat has shore power this would give an additional earth path if the earth wire in the lead to the shore power commection became faulty of the galvanic isolator became faulty
This earth / neutral connection now makes it important to get the phase connection of the shore power correct at it could put live power on the wrong side of the power switch and where as normally the live does through the switch first then the element / motor / etc second this is reversed. The down side is that if a live fault to earth occures the RCCD would trip when the fault occured where as with the phase connection correct this would only happen when the appliance was switch on.
I know this is very technical but would like comments from some of the electrical engineers around
nigelmercier
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[ QUOTE ]
I have an 1800w Sterling inverter on board, should it be earthed and if so where?
[/ QUOTE ]
Considering most (if not all) devices you plug in will be double-insulated with no earth lead, I wouldn't bother.
If you can, test if the case is connected to the negative input, if so, there is not much else you can do.
I have an 1800w Sterling inverter on board, should it be earthed and if so where?
[/ QUOTE ]
Considering most (if not all) devices you plug in will be double-insulated with no earth lead, I wouldn't bother.
If you can, test if the case is connected to the negative input, if so, there is not much else you can do.
boatmike
Well-Known Member
Spot on Steve! When I read this post I was going to say exactly the same thing. The point being that you are earthing the potentially dangerous high voltage current which should NEVER NEVER be earthed to battery negative. It should ALWAYS be seperately earthed to ground (meaning sea of course!)
graham
Well-Known Member
Personally if possible I would contact the manufacturers for advice on size and type of grounding needed.Difficult to sort the wheat from the chaffe among the replies on questions like this.
ean_p
Well-Known Member
Let me just play devils advocate here for a while..............so when you,ve conected the 'earth' tab of the inverter to the 'sea water', is not the negative side of most boat batteries then connected through the various sytems of 'bonding' etc that many people advocate...........also as the 'earth' on the inverter has to be internely connected to the neutral leg, have you not then connected the battery negative to the inverter neutral. And finaly as the 'earth', or neutral and/or line connections on the inverter have no original potential to the general mass of earth as they are not consious of it unlike a shore side supply ....then whats the point of it ?
answers please in 20 lines or less !
answers please in 20 lines or less !
boatmike
Well-Known Member
With respect your logic is faulty.
Consider that you have a 12 v or 24 volt DC system which is totally independent of the 240v AC current generated by the inverter. Just as in your house a short to earth through you can kill. So it can on a boat with greater likelyhood of it happening when things are wet. If you have an RCD on the supply this is a very good safeguard and it will work very well regardless of any earth just as it does ashore. Regardless of this, 240V and water are potentially dangerous and I would like to be sure that no fault in any device, or the inverter itself can cause 240V to earth through any human being who may well be wet and standing in a puddle. Granted, as someone else said, most devices are double insulated, but not all. Earthing the inverter to a hull plate ensures that any short to earth in any device, or wiring will go straight to ground and cause no harm. If what you say is correct we would not have an earthing system on any domestic wiring at home. If you have it there, why not on a boat?
Consider that you have a 12 v or 24 volt DC system which is totally independent of the 240v AC current generated by the inverter. Just as in your house a short to earth through you can kill. So it can on a boat with greater likelyhood of it happening when things are wet. If you have an RCD on the supply this is a very good safeguard and it will work very well regardless of any earth just as it does ashore. Regardless of this, 240V and water are potentially dangerous and I would like to be sure that no fault in any device, or the inverter itself can cause 240V to earth through any human being who may well be wet and standing in a puddle. Granted, as someone else said, most devices are double insulated, but not all. Earthing the inverter to a hull plate ensures that any short to earth in any device, or wiring will go straight to ground and cause no harm. If what you say is correct we would not have an earthing system on any domestic wiring at home. If you have it there, why not on a boat?
boatmike
Well-Known Member
Simply, the 240v earth is the line of least resistance DIRECTLY to the water around you. Just like a lightning conductor it has to carry a high EMF. The wiring on the 12v system will NOT be affected by a direct short to earth through this earth line any more than a lightning conductor connected to an external hull plate would. Or would you advocate connecting the lightning conductor to your battery negative using the same twisted logic?
ean_p
Well-Known Member
ahhhh a twisted logic eh!!!............ advocate i may have been but I didn't advocate anything, I was just asking questions of you good people out there that know far more then a simple seeker after truth like me. i didn't ask if connecting the inverter 'earth' to the battery negative would cause problems , only was it so that the inverter neutral (internaly connected to the inverter 'earth') would be joined to battery negative via the various bondings etc through the sea water , through the inverter'earth' back to the neutral. and so has not the battery negative (and therefore all negative wires etc)then brought to the same potential as the inverter neutral line.
Csail
N/A
Another spanner in the works! What if we use the earth plate method then either dry out or out for the winter?
steve_cronin
N/A
In those specific instances, you havn't got an earth but then you wouldn't by any other method unless you care to drop over the side with an earthing rod, in the case of drying out and thump it into the sand. When laid up ashore, mightn't you be connected to mains supply and therefore not be using the inverter at all?
Steve Cronin
Steve Cronin
fireball
Well-Known Member
But not nessersarily ... I've used the inverter whilst ashore - because I didn't need a huge amount of power - and the inverter was quicker than connecting the shore power.....
steve_cronin
N/A
Fine but we are talking about a 1.5kW inverter going live casing
So. by probability you will get away with it.
What the original poster needs to address is a permanent installation that is as safe as it can be.
If his kids are using it down below to power the DVD player and he takes a green one through an open hatch which swamps the inverter or it gets old and internal insulation breaks down - can happen - then he wants to be sure that any stray current goes immediately to earth and not through young Gemima's legs.
Don't you think?
Steve Cronin
So. by probability you will get away with it.
What the original poster needs to address is a permanent installation that is as safe as it can be.
If his kids are using it down below to power the DVD player and he takes a green one through an open hatch which swamps the inverter or it gets old and internal insulation breaks down - can happen - then he wants to be sure that any stray current goes immediately to earth and not through young Gemima's legs.
Don't you think?
Steve Cronin
fireball
Well-Known Member
Re: Fine but we are talking about a 1.5kW inverter going live casing
But the DVD player is double insulated - so doesn't have an earth anyway....
But the DVD player is double insulated - so doesn't have an earth anyway....