Should I earth my inverter?

[RAP77]

As the title Should I earth my inverter?
1Kw inverter supplying printer & microwave. It is wired as a TOTALLY separate circuit with no connection to the mains shore power circuits.
12 volt negative is connected to the shore power earth.

 

[VicS]

As the title Should I earth my inverter?
1Kw inverter supplying printer & microwave. It is wired as a TOTALLY separate circuit with no connection to the mains shore power circuits.
12 volt negative is connected to the shore power earth.

You dont say what inverter ( make and model) or if it is centre tapped or neutral earthed. If the latter does it have its own RCD or will you be using it with an external RCD.

 

[RAP77]

Not quite sure what you mean by centre tapped. Its not a transformer, it is a pure sine wave inverter 12 volt DC to 240 Volt AC.
The earth stud on the inverter is connected to the earth pin on the outlet (240 VAC) and nothing else.
The inverter is generic Chinese - can't remember the exact make.
Hope this helps
R

 

[superheat6k]

It is normal to connect the Neutral to earth at any power source and no where else. As it is not possible without very special equipment capable of panelling two separate supplies, to have more than one AC source at any one time, then the neutral should be grounded at the inverter, This might be an existing internal connection, and is simple to check with an ohmmeter - 0 ohms earth to ground at the inverter outlet with nothing else connected.

If you do not ground the neutral then the neutral can float to any voltage, and this could mean a risk if the neutral line became shorted to a non-earthed piece of metalwork somewhere.

 

[CLB]

It is normal to connect the Neutral to earth at any power source and no where else. As it is not possible without very special equipment capable of panelling two separate supplies, to have more than one AC source at any one time, then the neutral should be grounded at the inverter, This might be an existing internal connection, and is simple to check with an ohmmeter - 0 ohms earth to ground at the inverter outlet with nothing else connected.

If you do not ground the neutral then the neutral can float to any voltage, and this could mean a risk if the neutral line became shorted to a non-earthed piece of metalwork somewhere.

Thread resurrection, but having spent all morning reading through similar threads I though it might be easier to tag on to an existing one. Question for superheat6k, VisS and anyone else who knows a little on the subject:

If there is no continuity between the earth stud on the inverter casing and the neutral of the inverter outlet, is it safe to assume there is no internal connection between the two and that I should link earth to neutral at the inverter outlet.
There is full continuity, ie zero ohms, between the inverter casing/stud and the Earth pin on the inverter outlet.

I am planning on wiring it to the boat's shore power inlet wire through a 'break before make' two way switch so that the male pins of the shore power socket will never be live. This means that the current from the inverter will go through the boat's main breaker panel, which is fitted with an RCD.
Thanks

 

[PaulRainbow]

Would need to know the make and model of inverter, a link to data sheet/specifications etc would be useful. It's impossible to give detailed answers without. Be warned, connecting neutral and earth on some inverters will end in tears.

If you are fitting a changeover switch, it must be a two pole switch, so it switches the live and neutral.

 

[CLB]

Yep, just to confirm that switch is double pole.

The inverter is generic Chinese with very little in the way of specifications. Im struggling to post a link to it, but will try another computer.

Edit. This is the one.
https://www.solar-knight.com/index....-inverter-1000w-12-240v-pure-sine-wave-detail

 

[VicS]

Thread resurrection, but having spent all morning reading through similar threads I though it might be easier to tag on to an existing one. Question for superheat6k, VisS and anyone else who knows a little on the subject:

If there is no continuity between the earth stud on the inverter casing and the neutral of the inverter outlet, is it safe to assume there is no internal connection between the two and that I should link earth to neutral at the inverter outlet.
There is full continuity, ie zero ohms, between the inverter casing/stud and the Earth pin on the inverter outlet.

I am planning on wiring it to the boat's shore power inlet wire through a 'break before make' two way switch so that the male pins of the shore power socket will never be live. This means that the current from the inverter will go through the boat's main breaker panel, which is fitted with an RCD.
Thanks

I dont know if you have read this thread http://www.ybw.com/forums/showthread.php?517005-Wiring-in-2000w-inverter from about 18months ago but if you have you will realise the problem in answering what on the face of it is a simple question.


i think the best advice is to wire an inverter in the way the manufacturer specifies. If you buy a reputable make you should be able to get advice from them if necessary, but if you buy from an unknown far Eastern source you wlll be in the lap of whatever Gods or Idols are worshipped in the country of origin.

Do not connect the earth to the "neutral" unless the installation instructions say so. I suspect the output from many inverters mimics a centre tapped transformer winding, giveing the effect of two live conductors , each at 115 volts relative to earth.

The changeover switch you require is a 2 pole 2 way switch which breaks before it makes. You may find them described as a "transfer switch"

 

[Graham376]

My inverter is just wired into the boat supply before the rcd, via a double pole 2 way + off switch to isolate from deck socket, it works fine. As VicS mentions, unless the instructions for yours advise bridging, leave alone.

 

[PaulRainbow]

Yep, just to confirm that switch is double pole.

The inverter is generic Chinese with very little in the way of specifications. Im struggling to post a link to it, but will try another computer.

Edit. This is the one.
https://www.solar-knight.com/index....-inverter-1000w-12-240v-pure-sine-wave-detail

I'd agree with the comments not to bond the earth and negative of this particular inverter, unless instructions specifically say so, which i'd doubt.

What 240v equipment do you have onboard and what do you intend to run from the inverter ?

 

[CLB]

My inverter is just wired into the boat supply before the rcd, via a double pole 2 way + off switch to isolate from deck socket, it works fine. As VicS mentions, unless the instructions for yours advise bridging, leave alone.

Sounds like a plan

I'd agree with the comments not to bond the earth and negative of this particular inverter, unless instructions specifically say so, which i'd doubt.

What 240v equipment do you have onboard and what do you intend to run from the inverter ?

I intend to leave the 'sockets' circuit on when using the inverter. This will allow us to plug in a multitude of things, up to 1000w and taking into account the boat's battery capacity. Things like laptops (I work from the boat a lot) and probably the sub 1kw kettle when we are underway to save using gas. It's really a convenience thing that I will make some use of, but have until now lived without.

 

[PaulRainbow]

I intend to leave the 'sockets' circuit on when using the inverter. This will allow us to plug in a multitude of things, up to 1000w and taking into account the boat's battery capacity. Things like laptops (I work from the boat a lot) and probably the sub 1kw kettle when we are underway to save using gas. It's really a convenience thing that I will make some use of, but have until now lived without.

Be wary of statements such as "it works ok". Working "ok" and being safe are not always the same thing. I just finished re-wiring the shore power system on a boat that has been in the same ownership for 12 years, turns out, during those 12 years there has never been an RCD and the incoming shore power earth has not been connected to the boats earth circuit. All electrics, 32a inlet, everything worked, but hardly what you'd call safe.

I'd consider the inverter that you linked to a portable device, not something to be permanently installed, unlike something like a Victron inverter that can correctly be installed with an earth/neutral bond at source. It's likely that the inverter is centre tapped or pseudo centre tapped, which raises questions as to what happens if there is a fault, will the RCD trip, or will the inverter cut out (or will you get electrocuted) ? It's impossible to give definitive installation instructions without knowing how it works.

Some points though ;

Don't bond the earth and neutral unless the fitting instructions say so (i'll bet they don't).

You need to consider the earth connection and what happens in the event of a fault. Some of these types of inverters will shut down in the event of certain faults and it's claimed they don't need an RCD. Some may need to earth stud connecting to a suitable earthing point, that point will depend, to some extent, on the current installation. Is the shore power earth bonded to the boats bonding system (12v negative/anodes etc) ?

However you connect it, i'd get someone to connect an RCD tester and see what happens if there is a fault.

Rather than run laptops or phone chargers from the inverter, run them from DC-DC converters, most laptops can be connected with a car charger. Inverters are less efficient than a DC-DC converter.

Remember to turn the mains charger off when using the inverter, along with any heavy loads like water heaters.

 

[VicS]

I'd agree with the comments not to bond the earth and negative of this particular inverter, unless instructions specifically say so, which i'd doubt.

What 240v equipment do you have onboard and what do you intend to run from the inverter ?

Surely the DC negative will be earthed , unless the boat has an isolated DC system?

The question is whether or not one of the AC output conductors should be earthed to create a neutral. .... I say no unless the instructions say to do so because the earth connection in the the output sockets maybe a pseudo centre tap arrangement making each conductor 120 volt with respect to earth

Without a true neutral , ie one of the output connectors bonded to earth, the the boats shorepower system should be wired with double pole switches and double pole circuit breakers throughout as would be done for a "non polarised" shorepower system instead of with single pole switches and circuit breakers which we have on our more usual "polarised" AC shorepower systems

 

[superheat6k]

Thread resurrection, but having spent all morning reading through similar threads I though it might be easier to tag on to an existing one. Question for superheat6k, VisS and anyone else who knows a little on the subject:

If there is no continuity between the earth stud on the inverter casing and the neutral of the inverter outlet, is it safe to assume there is no internal connection between the two and that I should link earth to neutral at the inverter outlet.
There is full continuity, ie zero ohms, between the inverter casing/stud and the Earth pin on the inverter outlet.

I am planning on wiring it to the boat's shore power inlet wire through a 'break before make' two way switch so that the male pins of the shore power socket will never be live. This means that the current from the inverter will go through the boat's main breaker panel, which is fitted with an RCD.
Thanks

My way forward here would be ...

Firstly have you checked for nil continuity earth to neutral at a higher ohms scale. As long as their is no earth continuity at a higher scale, say k ohms rather than ohms (but not megohms), then, and in my workshop, I would plug in a small load such as a 60w light (do they still exist ???), apply to a decent 12 v source.

Measure output voltage between neutral and live - note this, then between earth and neutral and earth & live, if the reading from either earth to live or neutral is the same and around half the neutral to live then the thing is centre tapped and will not be suitable. If the levels are random and not balanced, or 0 volts, then likely the thing is not centre tapped.

So then next test, and note there is a minor risk something within the inverter might not like this test, with the 12 vdc power supply disconnected link the earth and neutral, then at a safe (non touching) distance connect to the DC supply.

If it works then check the neutral to earth voltage is 0 vac, and that live to earth is ~ 240v ±~10%.

Worse that will happen is the thing has a hissy fit, which is why it is important not to touch the thing whilst testing. If it is earth tapped at 110 v then find another inverter.

 

[PaulRainbow]

Surely the DC negative will be earthed , unless the boat has an isolated DC system?

The question is whether or not one of the AC output conductors should be earthed to create a neutral. .... I say no

No that was not the question, question was;

"is it safe to assume there is no internal connection between the two and that I should link earth to neutral at the inverter outlet"


I said "I'd agree with the comments not to bond the earth and negative of this particular inverter, unless instructions specifically say so, which i'd doubt."

I said it before and i'll say it again, just so we're all clear...... This is a portable device, it should not be fitted as if it were an inverter designed to be part of a fixed installation. To be part of a fixed installation, the earth and neutral should be bonded at source.

The previous thread that you linked to gives plenty of feedback, i'm not going through all of that again.

 

[VicS]

No that was not the question, question was;

"is it safe to assume there is no internal connection between the two and that I should link earth to neutral at the inverter outlet"


I said "I'd agree with the comments not to bond the earth and negative of this particular inverter, unless instructions specifically say so, which i'd doubt."

I said it before and i'll say it again, just so we're all clear...... This is a portable device, it should not be fitted as if it were an inverter designed to be part of a fixed installation. To be part of a fixed installation, the earth and neutral should be bonded at source.

The previous thread that you linked to gives plenty of feedback, i'm not going through all of that again.

I was confused by the fact that the original thread has been hijacked but the question now being asked is fundamentally the same.

CLB says there is no continuity between what he calls the neutral of the inverter output and the earth stud ( but there is between the earth pin ot the output and the earth stud.) Technically therefore there is no neutral. A neutral is only created by earthing one of the output conductors. He is asking, in effect, if he should do that.

You keep saying the earth and the negative of this inverter should not be bonded ........... BUT the DC negative will be bonded to earth. At least it should be unless the boat has an isolated DC system for some reason. You cannot locally unbond them at the inverter! However the earthing of the DC supply negative is not the issue . The questions are about the AC output from the inverter

 

[PaulRainbow]

You keep saying the earth and the negative of this inverter should not be bonded ...........

CLB asks "is it safe to assume there is no internal connection between the two and that I should link earth to neutral at the inverter outlet"

My answer is NO.

BUT the DC negative will be bonded to earth. At least it should be unless the boat has an isolated DC system for some reason. You cannot locally unbond them at the inverter! However the earthing of the DC supply negative is not the issue . The questions are about the AC output from the inverter

CLB is asking if he should connect the earth pin in the 3 pin receptacle of the inverter output to what would normally be the neutral terminal of the 3 pin receptacle, i'm simply saying he should not.

FYI millions and millions of boats do not have the vessel DC negative connected to the AC earth, that's a relatively recent thing. But that's got nothing to do with the question above.

I'm not talking about un-bonding any DC neg - AC earth connections.

The really short answer is unless the inverter can have the neutral and earth bonded at source, it isn't suitable for the intended installation.

 

[rogerthebodger]

CLB asks "is it safe to assume there is no internal connection between the two and that I should link earth to neutral at the inverter outlet"

My answer is NO.



CLB is asking if he should connect the earth pin in the 3 pin receptacle of the inverter output to what would normally be the neutral terminal of the 3 pin receptacle, i'm simply saying he should not.

FYI millions and millions of boats do not have the vessel DC negative connected to the AC earth, that's a relatively recent thing. But that's got nothing to do with the question above.

I'm not talking about un-bonding any DC neg - AC earth connections.

The really short answer is unless the inverter can have the neutral and earth bonded at source, it isn't suitable for the intended installation.

Paul can you please post a circuit diagram as a center tapped inverter as I would like to understand how it works.

I fully understand how a center tapped transformer works and its advantages in the real world.

This is what I found from Mr Google asked for "center tapped inverter"

 

[lw395]

If it was meant to be permanently installed, its output wouldn't be a 3 pin plug.

There are interesting possibilities for creating earth loops if you connect even the earth pin of the 3 pin socket back to the DC zero volts via the shorepower grounding.
Imagine that the inverter is drawing 100A.
Say your 'mains' earth wiring is 100mohm?
Guess your inverter DC return is 5 mohm?
What's the current flowing in the mains earth bonding and is that a good thing?

These inverters are OK for plugging in double insulated portable stuff. In a dry environment. Mostly. If you're careful.

Floating Neutral is not unsafe as such, it is just not the normal system used on yachts and may be illegal to do in some countries or get you thrown out of the trade. It needs care and understanding IMHO.

Mains on yachts is a can of worms. If you want a qualified person to approve it, it isn't cheap.

 

[PaulRainbow]

Paul can you please post a circuit diagram as a center tapped inverter as I would like to understand how it works.

I fully understand how a center tapped transformer works and its advantages in the real world.

The output transformer is centre tapped, same way as any other centre tapped transformer Roger.