Inverter earthing questions

[Alan S]

I am installing a 1500 Watt 48 Volt inverter in my boat and want to make sure it is safe and complies with the boat safety scheme.
Small GRP cruiser powered by 48V electric outboard kept on inland waterways.
No underwater metal of any sort - no through hull fittings below waterline, no anode apart from on outboard which is clear of water when tilted.
Shore power consumer unit has 2 pole circuit breaker and RCD feeding two sockets. The incoming earth wire goes to the sockets and nowhere else. The inverter has one 13A socket and a frame earthing stud. There is continuity between this stud and the socket earth pin but not the neutral.

When I am away from shore power I plan to use an extension lead fitted with an RCD plug to power small appliances (less than 1kW) from the inverter independently from the shore power sockets.

Where should I connect the inverter earth stud to?
Should the neutral not be connected to earth at some point?
What about a connection to the water and/or the DC system negative? (I don't want to drill any holes in the hull to fit a ground plate or anode).

Sorry if this has been asked before but I couldn't find a definitive answer.

 

[PaulRainbow]

Need to know the make and model of inverter please.

 

[rogerthebodger]

Where should I connect the inverter earth stud to?
Should the neutral not be connected to earth at some point?
What about a connection to the water and/or the DC system negative? (I don't want to drill any holes in the hull to fit a ground plate or anode).

Sorry if this has been asked before but I couldn't find a definitive answer.

Where should I connect the inverter earth stud to? Nothing as its got no real function
Should the neutral not be connected to earth at some point? Yes most deffinatly
What about a connection to the water and/or the DC system negative? No not in my view

Others will be along soom to tell m I am complete wrong ad the its unsafe but this is how my inverter is connected on my steel boat except I have a switch to change from shore power to inverter

 

[PaulRainbow]

Where should I connect the inverter earth stud to? Nothing as its got no real function
Should the neutral not be connected to earth at some point? Yes most deffinatly
What about a connection to the water and/or the DC system negative? No not in my view

Others will be along soom to tell m I am complete wrong ad the its unsafe but this is how my inverter is connected on my steel boat except I have a switch to change from shore power to inverter

Would anyone reading this post please disregard it as it is extremely dangerous.

 

[pmagowan]

I just like the optics of the potential court case;

So sir, would you like to tell the court where you got the advice regarding the wiring in question?
An internet forum m'lud
And who on this 'forum' gave the advice?
A person named 'Roger the bodger' m'lud

 

[rogerthebodger]

I just like the optics of the potential court case;

So sir, would you like to tell the court where you got the advice regarding the wiring in question?
An internet forum m'lud
And who on this 'forum' gave the advice?
A person named 'Roger the bodger' m'lud

So how should it be done ???

 

[PaulRainbow]

I could spend all afternoon (i won't though) quoting installations where the advice in post #3 would result in either an inverter going bang or someone potentially getting electrocuted. This is one of the most dangerous posts i have seen on PBO for a long time.

I just happen to have the installation manual for an inverter sitting on my PC desktop, an extract reads:

"When connecting the inverter earth, please note
that the earth wires for AC input and AC output are
connected inside and both are connected to the
inverter case. Use a suitable earthing cable to connect
the inverter casing to the boat’s earth or a bonding
system, vehicle chassis or an earthing rod (for
stationary installations)."

 

[rogerthebodger]

Would anyone reading this post please disregard it as it is extremely dangerous.

Would you please explain why this setup is extremely dangerous ???

It th same as a double insulated power tool with only 2 mains leads as the boat being plastic without any metal in the enviroment and without the return path to trip the RCD the power in the case of a falut will not disconnect

 

[PaulRainbow]

Would you please explain why this setup is extremely dangerous ???

It th same as a double insulated power tool with only 2 mains leads as the boat being plastic without any metal in the enviroment and without the return path to trip the RCD the power in the case of a falut will not disconnect

For one example, see post #7

For another, have you ever tried connecting neutral to Earth with a centre tapped inverter ?

No connection to the water, that's now a requirement on all new bulid boats and has been for decades.

Inverter installations should always follow the manufacturers installation instructions and will vay greatly from one to another, you cannot give "one size fits all" instructions.

 

[pmagowan]

So how should it be done ???

I'm not an electrician and there is insufficient information from the OP. Just found the exchange with a potentially lethal device entertaining, no insult intended.

 

[rogerthebodger]

I could spend all afternoon (i won't though) quoting installations where the advice in post #3 would result in either an inverter going bang or someone potentially getting electrocuted. This is one of the most dangerous posts i have seen on PBO for a long time.

I just happen to have the installation manual for an inverter sitting on my PC desktop, an extract reads:

"When connecting the inverter earth, please note
that the earth wires for AC input and AC output are
connected inside and both are connected to the
inverter case. Use a suitable earthing cable to connect
the inverter casing to the boat’s earth or a bonding
system, vehicle chassis or an earthing rod (for
stationary installations)."

So what AC input an inverter will only have a DC input.

The earth of the chassey is connected to the earth pin on the AC output so if there is a short in an appliance metal case in the appliance how is that power going to return to the supply / the neutral pin so there will be a difference current through the RCD to cause it to trip.

In a fixed insulation the earth point is an alternative current flow path back to the neutral supply together with the wired return

In a vehicle setup the tires will insulate the body of a car from the earth so its the wired protective return that will carry the leakage back to the neutral so the RCD can trip.

I too have degree level qualifications in both mechanical and electric engineering.and industrial design and insulation experience both in the UK and South Africa. where RCD's have been a requirement for much longer than the UK as I found when I attired.

stationary installations are very different to mobile and a steel boat is also very different to an insulated mobile insulation and should not be confused

On an instulated mobile what is the point of connection the inverter earthed chassis to the ground as the ground has not return to the neutral pin on the inverter

What is your level of electrical engineering qualifications so we all know.

 

[PaulRainbow]

So what AC input an inverter will only have a DC input.

The earth of the chassey is connected to the earth pin on the AC output so if there is a short in an appliance metal case in the appliance how is that power going to return to the supply / the neutral pin so there will be a difference current through the RCD to cause it to trip.

In a fixed insulation the earth point is an alternative current flow path back to the neutral supply together with the wired return

In a vehicle setup the tires will insulate the body of a car from the earth so its the wired protective return that will carry the leakage back to the neutral so the RCD can trip.

I too have degree level qualifications in both mechanical and electric engineering.and industrial design and insulation experience both in the UK and South Africa. where RCD's have been a requirement for much longer than the UK as I found when I attired.

stationary installations are very different to mobile and a steel boat is also very different to an insulated mobile insulation and should not be confused

On an instulated mobile what is the point of connection the inverter earthed chassis to the ground as the ground has not return to the neutral pin on the inverter

What is your level of electrical engineering qualifications so we all know.

Best part of 50 years in the automotive and marine industries.

Not interested in getting into one of your endless arguments where you just post dangerous rubbish. You have no idea what the inverter is that the OP intends to fit so you have no idea how it should be done.

Once more, for anyone reading this thread, please ignore the dangerous advice given here.

 

[rogerthebodger]

I'm not an electrician and there is insufficient information from the OP. Just found the exchange with a potentially lethal device entertaining, no insult intended.

I an not an electrician but I am an electrical engineer with qualifications at that level and several years industrial mechanical and electrical equipment design under my belt

Centre tapped transformers and inverters have the center tap as the neutral and protective earth connected to the center tap and the RCD connected across the 2 live connections. This has the effect of lowing the voltage between either line tap and earth to halt the voltage between the live outputs

outside work transformers/ invertors are nornally 110 voilt the thus lowers the voltahe to erount to 55 volts low enough to be onsidered safer that supply at 110 of 220

 

[rogerthebodger]

Best part of 50 years in the automotive and marine industries.

Not interested in getting into one of your endless arguments where you just post dangerous rubbish. You have no idea what the inverter is that the OP intends to fit so you have no idea how it should be done.

Once more, for anyone reading this thread, please ignore the dangerous advice given here.

I have over 60 years in both automotive and industrial design both electrical and mechanical design and becoming a Chartered Engineer (CEng) on the way

"Once more, for anyone reading this thread, please ignore the dangerous advice given here. "

In your opinion as an electrical technician "

 

[PaulRainbow]

I have over 60 years in both automotive and industrial design both electrical and mechanical design and becoming a Chartered Engineer (CEng) on the way

"Once more, for anyone reading this thread, please ignore the dangerous advice given here. "

In your opinion as an electrical technician "

Nothing to do with my opinion. When i install equipment i install it according to the manufacturers instructions and follow industry standards. I don't invent off the wall, bizarre ways of doing things just to be different.

 

[Refueler]

Alastair Garrods

ELECTRICS AFLOAT

May be an old book - but it was produced in co-op with PBO .... and it details the risks when earthing etc. - even to potential problem for people swimming near your 'earthed' boat ...

ISBN : 0-7136-6149-6

The problem is that not every Marina is wired same .... and this can lead to problems ...... and I would usually talk to Marina's Electrician to make sure of that Marinas situation.

 

[Alan S]

Need to know the make and model of inverter please.

Hi Paul, it's one of these...
CNSwipower Pure Sine Wave Inverter UPS With Charger 12, 24, 48VDC to 230VAC | eBay

 

[Moderator]

Thread locked pending review

 

[ean_p]

Hi Paul, it's one of these...
CNSwipower Pure Sine Wave Inverter UPS With Charger 12, 24, 48VDC to 230VAC | eBay

you may like to watch this strip down vid on that brand......

 

[Alan S]

you may like to watch this strip down vid on that brand......

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