Fitting an inverter

[Guest st170dw]

I am going to replace the inverter on my boat in the new year and I am not sure how the earth should be wired.

 

When I took it off there was a wire from the earth post on the back to the negative 12 volt terminal. This wire appeared to have overheated at some time in its life.

 

I have a rcd and a polarity detector between the inverter and the 240 volt sockets.

 

Can anyone help?

 

Dave

[Guest]

I am going to replace the inverter on my boat in the new year and I am not sure how the earth should be wired.

 

When I took it off there was a wire from the earth post on the back to the negative 12 volt terminal. This wire appeared to have overheated at some time in its life.

 

I have a rcd and a polarity detector between the inverter and the 240 volt sockets.

 

Can anyone help?

 

Dave

We have had this one before! Here is how ours is wired (it is a 3kw pure sine wave sterling). Pos and neg from battery via isolator and 200amp fuse to inverter-nothing connected to earth on low volt DC side. AC 240v out via rcd and two way domestic fuse board combined ("garage" consumer unit from Screwfix). There is an earth terminal which is connected to the steel hull of the boat on the 240v side. Some inverters do not have such an earth terminal and the consensus of opinion was that these inverters did not require connecting to earth. If in doubt check with the manufacturer.

I can't understand why the 12 volt side had been grounded on your old unit though, unless your boat uses the shell as an earth return. This is not normal procedure now. If the insulation on this wire was melted it was probably not up to the current required or it was badly connected.

[Guest st170dw]

We have had this one before! Here is how ours is wired (it is a 3kw pure sine wave sterling). Pos and neg from battery via isolator and 200amp fuse to inverter-nothing connected to earth on low volt DC side. AC 240v out via rcd and two way domestic fuse board combined ("garage" consumer unit from Screwfix). There is an earth terminal which is connected to the steel hull of the boat on the 240v side. Some inverters do not have such an earth terminal and the consensus of opinion was that these inverters did not require connecting to earth. If in doubt check with the manufacturer.

I can't understand why the 12 volt side had been grounded on your old unit though, unless your boat uses the shell as an earth return. This is not normal procedure now. If the insulation on this wire was melted it was probably not up to the current required or it was badly connected.

 

 

I couldn't understand why the 12 volt side had been grounded either. The wire from the inverter's earting point to the negative was much thinner than those used for the 12v positive and negative. Would that not have had the effect of making the boat's shell negative?

 

I intend to attach a wire from the earth terminal to the bolts that hold the inverter on to the shell which would provide a good earth. If there is a problem with the inverter would that not then make the shell live? Obviously any problems within the cabin are covered by the consumer unit with rcd on the 240 volt side.

Edited December 21, 2005 by st170dw

[Guest]

I couldn't understand why the 12 volt side had been grounded either. The wire from the inverter's earting point to the negative was much thinner than those used for the 12v positive and negative. Would that not have had the effect of making the boat's shell negative?

Yes that wire would have made the shell negative-can't see the point in that personally.

I intend to attach a wire from the earth terminal to the bolts that hold the inverter on to the shell which would provide a good earth. If there is a problem with the inverter would that not then make the shell live? Obviously any problems within the cabin are covered by the consumer unit with rcd on the 240 volt side.

 

What make/spec is your new inverter? Has your new inverter got an external terminal with the earth symbol or similar on it? If so it is normal to earth that to the steel shell. All that will do is make the inverter earth and the shell at the same potential. If then in the unlikely event that a live wire came into contact with the shell, then the RCD would trip. Most people with the smaller type inverter which simply plug into a 12v socket dont seem to bother with an earth to the shell. When we are using our generator there is no provision from the generator for an earth to the shell.

[Gary Peacock]

 

This is how the BMEA and RCD regs say it should be.

 

In reality most modern installations feature some form of "Auto change over" between shore, generator and inverter the Main Circuit in the right hand diagram would be better described as a heavy load circuit for washing machine/cooker etc.

Edited December 21, 2005 by Gary Peacock

[Guest st170dw]

Catweasel,

 

Thanks for your replies. It makes sense to me now. It was the attachment of the wire to the 12v negative that threw me - I couldn't for the life of me see the reason for it.

 

I have not yet bought a new one since the old one is currently with the manufacturer to see what has gone wrong with it after only 18 months. If I replace like for like it will have an earth post. That was where the wire to the 12v negative was attached.

 

Gary,

 

Thanks for the diagrams. My changeover from shoreline is accomplished by either plugging the inverter or the shoreline into the input 240v socket. It is therefore impossible to have both operating at the same time. A piece of KISS engineering

 

Dave

Edited December 21, 2005 by st170dw

[Guest]

Catweasel,

 

Thanks for your replies. It makes sense to me now. It was the attachment of the wire to the 12v negative that threw me - I couldn't for the life of me see the reason for it.

 

I have not yet bought a new one since the old one is currently with the manufacturer to see what has gone wrong with it after only 18 months. If I replace like for like it will have an earth post. That was where the wire to the 12v negative was attached.

 

Gary,

 

Thanks for the diagrams. My changeover from shoreline is accomplished by either plugging the inverter or the shoreline into the input 240v socket. It is therefore impossible to have both operating at the same time. A piece of KISS engineering

Dave

That is what my mate has done on his NB. Simple and foolproof in my opinion. Gary's post is interesting in that it is the first time I have seen it in writnig that the protective conductor must be earthed. That solves that one then.

Edited December 21, 2005 by Guest

[ChrisPy]

. My changeover from shoreline is accomplished by either plugging the inverter or the shoreline into the input 240v socket. It is therefore impossible to have both operating at the same time. A piece of KISS engineering

 

Dave

better to plug the input 240V plug into the inverter or shoreline socket, no??

[Guest]

better to plug the input 240V plug into the inverter or shoreline socket, no??

I think it is the wording here! My mates boat has the standard blue inlet at the stern of his boat which feeds all 240v circuits on board. He can either plug his shoreline into it as normal, or the 240v outlet of his inverter into it. But not both!

[DHutch]

KISS engineering

Thats "Keep It Simple and Straightforward" then! (this is what one of our lecturers says as act of poltical correctness)

 

On a more serouse note, i think pluging the inverter into the shorline socket is a bit of a tacky way of doing it, and not what i would do.

- Also, ive you are replacing the inverter, i would consider fitting victron inverter/charger.

- Ive never used one, but i think if i ever wanted 240v on the boat thats what i'd be looking at doing.

 

 

Daniel

[Guest]

I like the Sterling pure sine inverter-no change over switch needed owing to UPS design. Reliable stand by mode saves power. Everything has worked fine that we have plugged into it. My one criticism is that the cooling fan is a little noisy. We need a seperate charger though (Sterling 40amp)

[DHutch]

I like the Sterling pure sine inverter-no change over switch needed owing to UPS design.

 

My one criticism is that the cooling fan is a little noisy.

Yeah, i think that even if you dont go down the combined charger/inverter route a inverter with built in 'UPS' is clearly the best way, they seem very reliable, and allows you to keep everything else simple and lodigical.

 

I also agree about the fan, we have a (now 15yo) sterling threeway mains charger, and the fan can be a bit annoying.

- One day i will rip it out and put a larger/quieter one in its place.

 

 

Daniel

[Guest st170dw]

Thats "Keep It Simple and Straightforward" then! (this is what one of our lecturers says as act of poltical correctness)

 

On a more serouse note, i think pluging the inverter into the shorline socket is a bit of a tacky way of doing it, and not what i would do.

- Also, ive you are replacing the inverter, i would consider fitting victron inverter/charger.

- Ive never used one, but i think if i ever wanted 240v on the boat thats what i'd be looking at doing.

Daniel

 

At the risk of being a heretic I agree with the principal arguments of John Orantes - If you want the luxury of a house buy a cottage!

 

I use my inverter to provide tv and M.A.S.H dvds in the middle of nowhere. I have used shore power once in the past year for 48 hours at Llangollen. I don't have a battery charger on the boat other than the engine and in my opinion that is a good way to persuade the OCM to cruise rather than sitting stationery!

 

Dave

 

better to plug the input 240V plug into the inverter or shoreline socket, no??

 

Sorry Chris,

 

Bad description on my part - a 240v plug is plugged into the inverter, then a second socket input into the cabin.

 

I can therefore use the inverter without energising the cabin 240v.

 

Dave

[Guest]

It is worth having an inverter just to watch MASH! Brilliant

[ChrisPy]

 

Bad description on my part - a 240v plug is plugged into the inverter, then a second socket input into the cabin.

 

............. I just hated the idea of someone getting an unexpected Xmas tingle from a live plug !!

 

stupidly I once did something similar. trying to rectify a fault on an electric drill connected to an extension lead, I took the plug apart and checked it. No problem. Then I did the same on the socket - WHAM !!

[hnb2907]

This is an interesting one. The schematic shows the neutral line connected to the hull, but what about the chassis earth on the inverter? I'm not surprised about the neutral connection as domestic mains is usually connected to earth anyway.

 

I've recently fitted a 2kw inverter to my boat. The installation isn't finished yet as it's not earthed yet due to running out of time on my visit.

I did get as far as powering it up and used the 500watt heater in the calorifier to test it. At this point, the inverter chassis gave me an almost pleasant 50hz buzz while holding on to the metalwork of the boat. Again, not too surprised by this happening, it is obviously because it's electrically floating and found a high resistance path around the whole setup (probably through the engine coolant water and then myself) .

 

So, my thought is that the schematics diagram above should have both neutral and its chassis earth point both connnected to the hull, which it doesn't show. Is there some narrative that goes with the schematic, as after a quick search I haven't found the directive it comes from. Anyone got any thoughts?

 

By the way, I don't condone doing daft electrical experiments like myself, we all know what happens with electrickery - I'm supposedly a professional electronics engineer and expected to get a small belt, rather than a tingle! And I'll be going back to finish it off before my parents get the chance to go anywhere near it.

 

 

Cheers,

Chris.