Inverter earthing questions

[PaulRainbow]

Thanks for the video. It offers some reassurance about the quality but I'm still in the dark about earthing arrangements.

The manual isn't at all helpful.

Do not attempt to bond the "neutral" and Earth.

The Earth stud is exactly what it says on it, it must be connected to Earth. On a boat, that means the water. As you have no underwater metal you will need to fit something. All you need to do is fit a small button anode. Do not connect anything else to this anode, make no connections to the boats DC system. If you were to connect the shore power Earth to the anode you would need to fit a galvanic isolator.

If this inverter came with battery cable like the ones in the video above, don't use them. Use 25mm battery cables and fit a 150a fuse. I would make sure there is an isolator between the batteries and the inverter too.

Remember, this will put out 240v, just the same as your house electricity and can kill you just the same too.

 

[[2574]]

The manual isn't at all helpful.

Do not attempt to bond the "neutral" and Earth.

The Earth stud is exactly what it says on it, it must be connected to Earth. On a boat, that means the water. As you have no underwater metal you will need to fit something. All you need to do is fit a small button anode. Do not connect anything else to this anode, make no connections to the boats DC system. If you were to connect the shore power Earth to the anode you would need to fit a galvanic isolator.

If this inverter came with battery cable like the ones in the video above, don't use them. Use 25mm battery cables and fit a 150a fuse. I would make sure there is an isolator between the batteries and the inverter too.

Remember, this will put out 140v, just the same as your house electricity and can kill you just the same too.

Paul,

think you meant 240v.

Rob

 

[Alan S]

If this inverter came with battery cable like the ones in the video above, don't use them. Use 25mm battery cables and fit a 150a fuse. I would make sure there is an isolator between the batteries and the inverter too.

Bearing in mind it's a 48V inverter I used 16mm² cables total length <1m and 50A fuse downstream from the main 160A fuse ind isolator. Max current should be about 30-40A so do you think that's OK?
Your comments about earthing seem logical to me so I'll go along with that.
I found a BSS checklist online (see screenshot) which seems to suggest the output from the inverter should go through a consumer unit. Should I connect the inverter via a changeover switch upstream of the shore power consumer unit? Not really keen on that, my idea was to keep the two ac systems completely independent. Comments appreciated.

 

[PaulRainbow]

Paul,

think you meant 240v.

Rob

Yes, 240v, will edit the original.

 

[rotrax]

I have just fitted a 3000W - 1500W continuous - inverter. I followed the instructions and there is no mention of earthing it. Red and black heavy battery cables to the house bank bus bars, three pin 13 amp plug wired as normal to a new socket mounted in a convenient location for the outlet. Works fine too.

 

[Alan S]

I have just fitted a 3000W - 1500W continuous - inverter. I followed the instructions and there is no mention of earthing it. Red and black heavy battery cables to the house bank bus bars, three pin 13 amp plug wired as normal to a new socket mounted in a convenient location for the outlet. Works fine too.

Sounds good but is it absolutely safe under fault conditions and is it compliant with Boat Safety Scheme for inland waterways?

 

[PaulRainbow]

Bearing in mind it's a 48V inverter I used 16mm² cables total length <1m and 50A fuse downstream from the main 160A fuse ind insulator. Max current should be about 30-40A so do you think that's OK?

I forgot you're 48v Alan, so yes, that's fine.

Your comments about earthing seem logical to me so I'll go along with that.

I found a BSS checklist online (see screenshot) which seems to suggest the output from the inverter should go through a consumer unit. Should I connect the inverter via a changeover switch upstream of the shore power consumer unit? Not really keen on that, my idea was to keep the two actors systems completely independent. Comments appreciated.

I don't see where the inverter offers any RCD type protection, over voltage might be protected by the inverter, but it's not entirely clear. You did indicate in your first post that you would use a plug in RCD though.

I see two ways of making a decent job of it:

1) Fit a small enclosure, with a 6a RCBO in it, connect this to the inverter. From the RCBO connect a couple of sockets. This keeps it independent from the shore power system, it's safe and should comply with the BSS.

2) Fit a changeover switch, connect the shore power and inverter to the switch, with the output going to the consumer unit. The inverter Earth should go to the consumer unit Earth busbar, with a new wire going from the busbar to a connection to the water (small anode in your case). You will then need to fit a galvanic isolator to the incoming shore power Earth. This is a proper fixed installation, it is safe and complies with the BSS and all other current regulations.

With option 2 you need to consider what is connected to the consumer unit, there may be things that you won't want to run from the inverter, water heater, battery charger etc.

Both systems still require the inverter case to be Earthed.

 

[PaulRainbow]

I have just fitted a 3000W - 1500W continuous - inverter. I followed the instructions and there is no mention of earthing it. Red and black heavy battery cables to the house bank bus bars, three pin 13 amp plug wired as normal to a new socket mounted in a convenient location for the outlet. Works fine too.

There is no mention in the instructions for the OPs inverter regarding an Earth, but the case has a clearly marked Earth point.

But not every inverter is the same, so there are no "one size fits all" fitting instructions.

Also, working fine and being safe in a fault situation can be two entirely separate things.

 

[Alan S]

Thanks Paul. I think I'll go with option 1. If I fit just one socket it stops me accidentally overloading the inverter with 2 or more appliances at the same time. RCBO is that a combined earth leakage and over current device? which I suppose is the bare bones of a minimalist consumer unit.

 

[PaulRainbow]

Thanks Paul. I think I'll go with option 1. If I fit just one socket it stops me accidentally overloading the inverter with 2 or more appliances at the same time. RCBO is that a combined earth leakage and over current device? which I suppose is the bare bones of a minimalist consumer unit.

That's correct, should comply with the BSS.

 

[Helidan]

Sorry to jump in here guys but I have a question that is essentially on topic. If one of those portable solar lithium power stations with inverter was to be used on a boat (GRP in my case) is there any special considerations to prevent shock hazards? We had the idea of using one to power a camping kettle, TV, laptop etc and also act as a emergency standby source for our main systems.

 

[rotrax]

Sounds good but is it absolutely safe under fault conditions and is it compliant with Boat Safety Scheme for inland waterways?

The BSS is not relevant. My vessel is on the ocean, not on a canal or river.

It came from a trusted supplier and has good reviews.

I am prudent and safety concious but also a very experienced mechanic with substantial general electrical, hydraulic and pneumatic experience.

If the device failed and allowed the casing to be live, I would be in trouble if I touched it.

But that goes for all sorts of household and leisure equipment. The chances of that type of fault are very low.

My maternal Grandmother was electrocuted to death by a faulty mains radio set in 1957.

Things have moved on a bit since then in regard to safety.

 

[Alan S]

2) Fit a changeover switch, connect the shore power and inverter to the switch, with the output going to the consumer unit. The inverter Earth should go to the consumer unit Earth busbar, with a new wire going from the busbar to a connection to the water (small anode in your case). You will then need to fit a galvanic isolator to the incoming shore power Earth. This is a proper fixed installation, it is safe and complies with the BSS and all other current regulations.

Paul, re-considering your option 2, it's probably a better solution for my needs. There is still one thing I'm not sure about, the earth wire in the 3 core cable from the inverter plug/socket seems to be redundant if I have understood your description. The attached sketch may show what I mean.

 

[Alan S]

The BSS is not relevant. My vessel is on the ocean, not on a canal or river.

It came from a trusted supplier and has good reviews.

I am prudent and safety concious but also a very experienced mechanic with substantial general electrical, hydraulic and pneumatic experience.

If the device failed and allowed the casing to be live, I would be in trouble if I touched it.

But that goes for all sorts of household and leisure equipment. The chances of that type of fault are very low.

My maternal Grandmother was electrocuted to death by a faulty mains radio set in 1957.

Things have moved on a bit since then in regard to safety.

The BSS is relevant to me, the OP.
Also I do not want to be electrocuted by a faulty appliance. Good installation practices should prevent this.

 

[Refueler]

I refer again to Alastair Garrods excellent book .....

The matter of earthing is given serious write-up in the book and shows what can happen ... not only the dangers but also the interaction of boats near each other.
Recommendations read in the thread impact directly on whats written in that book ... I suggest caution and not to just be led by forum talk. For me - I have qualifications in AC and DC theory and applications ... but I do not wish to risk anything ..... because Marine installations cannot and should not be regarded same as in your house .... the environment has potential to kill.

To quote from the book :

Bringing AC shore power on board a boat in a marine environment is dangerous enough and it becomes more dangerous when people make the mistake of applying shoreside DIY practices to the world afloat. Conflict or confusion occurs between earthing the appliance, earthing the boat and earthing to the shore network.

I'd scan and post the pages - but its Copyright of AG and PBO .... given that the book deals with everything from choice of batterys (I accept pre Lithium) all way through to wiring up AC and DC .... charging ... etc. Its well worth the price .....

 

[PaulRainbow]

Paul, re-considering your option 2, it's probably a better solution for my needs. There is still one thing I'm not sure about, the earth wire in the 3 core cable from the inverter plug/socket seems to be redundant if I have understood your description. The attached sketch may show what I mean.

Option 2 is a proper fixed installation, this complies fully with the BSS and all current standards for new build boats.

In post #1 you said "There is continuity between this stud and the socket earth pin but not the neutral"

If that is correct, there will be continuity between the Earth connections of any appliance connected to the inverter, the inverter case and "Earth". When connected to shore power you will have a connection to the marina Earth and the water, when away from shore power you will have a connection to the water.

Any doubt whatsoever about continuity between the socket Earth and the stud, connect the Earth wire in the 3 core cable to the consumer unit busbar.

 

[Helidan]

Option 2 is a proper fixed installation, this complies fully with the BSS and all current standards for new build boats.

In post #1 you said "There is continuity between this stud and the socket earth pin but not the neutral"

If that is correct, there will be continuity between the Earth connections of any appliance connected to the inverter, the inverter case and "Earth". When connected to shore power you will have a connection to the marina Earth and the water, when away from shore power you will have a connection to the water.

Any doubt whatsoever about continuity between the socket Earth and the stud, connect the Earth wire in the 3 core cable to the consumer unit busbar.

what is the standard for new builds? Is it incorporated into the Recreational Craft Directive?

 

[PaulRainbow]

I refer again to Alastair Garrods excellent book .....

The matter of earthing is given serious write-up in the book and shows what can happen ... not only the dangers but also the interaction of boats near each other.
Recommendations read in the thread impact directly on whats written in that book ... I suggest caution and not to just be led by forum talk. For me - I have qualifications in AC and DC theory and applications ... but I do not wish to risk anything ..... because Marine installations cannot and should not be regarded same as in your house .... the environment has potential to kill.

This is good advice, people often forget that marine installations differ to domestic or commercial, land based installations.

The advice i have given the OP isn't some theory i've dreamt up (not suggestion you have said it is), it is industry standard and best practice. It is exactly how all current standards, ISOs etc say that it should be done.

Inverter installations are a particular concern of mine, a lot of people seem to think that, just because the power is coming from batteries, it is somehow different to the electricity that comes from the wall sockets in their house. I have seen some very shoddy and dangerous inverter installations and even had a few electric shocks when working on boats with bad installations.

 

[PaulRainbow]

what is the standard for new builds? Is it incorporated into the Recreational Craft Directive?

EU boats must comply with the RCD, UK boats now have to comply with the RCR, essentially the same thing. Both are subject to standards set out in various ISOs.

 

[PaulRainbow]

Sorry to jump in here guys but I have a question that is essentially on topic. If one of those portable solar lithium power stations with inverter was to be used on a boat (GRP in my case) is there any special considerations to prevent shock hazards? We had the idea of using one to power a camping kettle, TV, laptop etc and also act as a emergency standby source for our main systems.

Without knowing the exact specifications of the power station this is impossible to answer.