Inverter 12V to 240 V AC How to earth?

[Alex_Blackwood]

Having read this thread with some interest. Can I suggest that the OP would appear to have a very limited knowledge and understanding of the purchase and installation of the equipment, also of the professional advice given in the thread. Perhaps he would be better advised to seek local advice from a professional regarding the purchase and installation. I am in no way intending to be critical of the OP but we all have differing levels of expertise and competency and sometimes in the interest of safety and peace of mind leaving it to a professional is a better option.

 

[ylop]

Good question, i did ask what sort of output the OP was planning to fit. Some more information would be useful.

Indeed but you jumped down the throat of the person in post 2 who asked how many Watts which is essentially the same question!

 

[PaulRainbow]

Indeed but you jumped down the throat of the person in post 2 who asked how many Watts which is essentially the same question!

Watts are irrelevant in the context of whether an inverter needs an Earth or not. A low wattage inverter still produces 240V AC, which can kill you.

Make, model, power output and usage, etc have a bearing on how the inverter is installed or even if it is suitable for installing on a boat. Unfortunately, despite being asked more than once, the OP has provided zero information on his proposed installation.

 

[ylop]

Watts are irrelevant in the context of whether an inverter needs an Earth or not. A low wattage inverter still produces 240V AC, which can kill you.

Make, model, power output and usage, etc have a bearing on how the inverter is installed or even if it is suitable for installing on a boat. Unfortunately, despite being asked more than once, the OP has provided zero information on his proposed installation.

Well if it’s a 100W “cigarette lighter” style one it won’t have an Earth connection. I agree that’s a risk, but depending what you are doing with it (eg only using it to charge a powertool battery which was a double insulated charger, which sits on the chart table right next to the mini inverter) it might be an acceptable risk. Then the next “size” up typically aren’t wired via a consumer unit as you described but have an integral socket, but do have an Earth connection. Examples of this type from credible brands such as sterling come with boat installation instructions.

The OP did say at the end of post 8 that 1000W may be enough for his modest needs I suspect the OP hasn’t provided further detail because he doesn’t actually know. He perhaps feels 240V would be useful without a specific use in mind. He also mentioned installing in a caravan - and I can see if you were doing two installs that the same approach would have some appeal, especially if you were not particularly au fait with electricity.

If I was the OP, I’d go elsewhere for the advice, because whilst what you get here especially around electrics is probably good (once you can filter the bad) it’s often delivered in a particularly abrasive way.

 

[PaulRainbow]

Well if it’s a 100W “cigarette lighter” style one it won’t have an Earth connection. I agree that’s a risk, but depending what you are doing with it (eg only using it to charge a powertool battery which was a double insulated charger, which sits on the chart table right next to the mini inverter) it might be an acceptable risk. Then the next “size” up typically aren’t wired via a consumer unit as you described but have an integral socket, but do have an Earth connection. Examples of this type from credible brands such as sterling come with boat installation instructions.

The OP did say at the end of post 8 that 1000W may be enough for his modest needs I suspect the OP hasn’t provided further detail because he doesn’t actually know. He perhaps feels 240V would be useful without a specific use in mind. He also mentioned installing in a caravan - and I can see if you were doing two installs that the same approach would have some appeal, especially if you were not particularly au fait with electricity.

If I was the OP, I’d go elsewhere for the advice, because whilst what you get here especially around electrics is probably good (once you can filter the bad) it’s often delivered in a particularly abrasive way.

You just demonstrated that there are many variables that will affect the installation and without more information it's just a guessing game.

So, asking for sufficient information to allow a definitive answer is abrasive, really ?

See the final paragraph of post #6. I don't know why i ever bother to reply to inverter threads, they always end the same.

 

[ylop]

You just demonstrated that there are many variables that will affect the installation and without more information it's just a guessing game.

So, asking for sufficient information to allow a definitive answer is abrasive, really ?

See the final paragraph of post #6. I don't know why i ever bother to reply to inverter threads, they always end the same.

No, asking questions is a perfectly sensible thing to do. It’s how you ask them, or how your reply to the answer that the person answering them gives you (if they knew all you know they wouldn’t need to be asking for advice). Or indeed how you respond to others who contribute their own questions.

Have you considered the problem may not be inverter threads but how you choose to approach them?

 

[PaulRainbow]

No, asking questions is a perfectly sensible thing to do. It’s how you ask them, or how your reply to the answer that the person answering them gives you (if they knew all you know they wouldn’t need to be asking for advice). Or indeed how you respond to others who contribute their own questions.

Have you considered the problem may not be inverter threads but how you choose to approach them?

Only question i asked was;

"Where are you going to fit an inverter, boat/caravan, or camper ? Exactly what make/model are you fitting ?"

The usual problem with inverter threads is incorrect input from people who don't know what they are talking about, but insist that they do, giving incorrect and dangerous advice.

I'm generally busy and tend to post between jobs, or as has been the case over the past 2 years when i've been feeling well enough, so my posts are often concise. But If you don't like my posting style don't read my posts, stick me in your block list.

 

[ylop]

Only question i asked was;

"Where are you going to fit an inverter, boat/caravan, or camper ? Exactly what make/model are you fitting ?"

Except it wasn’t! You started with this:

What relevance are Watts ?

But ironically asked the same question a different way in a later post:

What sort of output are you thinking of ?

And then this wasn’t a direct question but it did seem like a rhetorical “why are you ignoring me”

Not sure why you need to do a lot more reading up, i've told you how to wire it.

I'm generally busy and tend to post between jobs, or as has been the case over the past 2 years when i've been feeling well enough, so my posts are often concise. But If you don't like my posting style don't read my posts, stick me in your block list.

I don’t have anyone on ignore - I think ignoring responses you don’t like puts you in an Echo Chamber where you start to believe your voice is the only or best way to look at a situation. I have no issue with your technical advice so it would be counter productive to ignore you. I was actually trying to help you have a more enjoyable encounter with the forum - but perhaps you actually relish the hostility (I note that nobody has actually contradicted your technical advice as you predicted), but you set the tone from post 3.

 

[Cerebus]

I agree with a lot that has been said.

I noted NO abrasive replies.

I am grateful to Paul for his information.

I was thinking of having an inverter and wondered what it needed for installation.

I have decided I do not really need an inverter and will continue with my 12volt chargers.

I learned a lot however especially about the ‘magical’ earthing system that sellers of inverters I have seen DO NOT mention, so thanks for that.

 

[penberth3]

@PaulRainbow was right. Inverter threads should all stop at Post #4.

 

[Skipper Felice]

Victron have a downloadable .pdf on their website..."Victron Wiring Unlimited" which has a lot of informationn and explanation on earthing inverters.

This Victron paper is the best reading about power and wiering for a boat: I explains most things of importance !

 

[PabloPicasso]

Why bond the earth and neutral together?

How would the earth function differently from the neutral if they are permanently connected? Neutral would be connected to the hull button anode then?

In my ignorance this makes no sense? Can someone explain this for me?

(i am not fitting an inverter, just curious)

Thanks

 

[Alex_Blackwood]

I hear wet string, salt water rather than fresh, is the current wire of choice.

You may find some resistance and potentially a difference to that line of thought.

 

[JOHNPEET]

You need one where the Earth and neutral can be bonded at the inverter.

Not sure why you need to do a lot more reading up, i've told you how to wire it.

Connect the DC positive and live to the inverter, with a suitable fuse close to the battery. Bond the Earth and neutral at the inverter. Connect Live, neutral and Earth to a consumer unit, fitted with a RCD and MCBs for individual circuits. Connect an Earth wire from the consumer unit Earth busbar to the water.

Can I suggest that the AC Earth be terminated on the DC Neg Bus, then a single bonding cable taken from the DC Neg Bus to the “water earth” - be it an anode or the hull of a steel boat. This arrangement will ensure the AC supply RCD/RCBO trips, should a fault develop which results in 230v leaking onto the DC system or steel hull. Apologies Paul if you’ve covered this elsewhere within the thread (did check but may have missed it)

 

[jakew009]

Why bond the earth and neutral together?

How would the earth function differently from the neutral if they are permanently connected? Neutral would be connected to the hull button anode then?

In my ignorance this makes no sense? Can someone explain this for me?

(i am not fitting an inverter, just curious)

Thanks

RCDs work by sensing a current imbalance between the live and neutral wire.

Let’s imagine a live wire inside your water heater comes free and touches the metal case. Imagine the water heater is being powered by your inverter.

The metal case is now at 230v with respect to earth.

The metal case of the water heater is likely connected to earth via the green and yellow wire (in this case the sea water).

However, there is no path from the sea water back to the inverter. Therefore no current actually flows and the RCD doesn’t trip.

Now imagine you go fiddling around in the locker and manage to touch both the inverter case and the water heater case at the same time. Bang. You just got an electric shock.

If you had a bond between the neutral and earth, as soon as that live wire in your water heater touched the earthed case, the RCD would have tripped.

There are valid scenarios with an inverter when you don’t bond the neutral and the earth (known as an IT system) which is similar to the 110V systems used on building sites but that’s a bit beyond the scope of your question.

It’s also worth remembering that even in your house, the earth and neutral are bonded. Generally in the service cutout on the side of your house if it’s a PME earth.

 

[PaulRainbow]

RCDs work by sensing a current imbalance between the live and neutral wire.

Let’s imagine a live wire inside your water heater comes free and touches the metal case. Imagine the water heater is being powered by your inverter.

The metal case is now at 230v with respect to earth.

The metal case of the water heater is likely connected to earth via the green and yellow wire (in this case the sea water).

However, there is no path from the sea water back to the inverter. Therefore no current actually flows and the RCD doesn’t trip.

Now imagine you go fiddling around in the locker and manage to touch both the inverter case and the water heater case at the same time. Bang. You just got an electric shock.

If you had a bond between the neutral and earth, as soon as that live wire in your water heater touched the earthed case, the RCD would have tripped.

There are valid scenarios with an inverter when you don’t bond the neutral and the earth (known as an IT system) which is similar to the 110V systems used on building sites but that’s a bit beyond the scope of your question.

Just for clarity, fixed inverter installations must have the earth and neutral bonded.

It’s also worth remembering that even in your house, the earth and neutral are bonded. Generally in the service cutout on the side of your house if it’s a PME earth.

 

[jakew009]

Just for clarity, fixed inverter installations must have the earth and neutral bonded.

Yep and that’s because the “second fault” condition on an isolated system is really really nasty.

Live wire in kettle touches metal case - that’s now live but there is no risk as no return path back to inverter.

Some time later a neutral wire in the bilge makes contact with water inadvertently “earthing” it.

Now someone stood in damp salty cockpit with bare feet touches kettle bang you are now dead with no RCD to save you.

 

[wonkywinch]

As they say, "it's the volts that jolts but the mills that kills". Mills being milliamps.

100mA (0.1A) can kill you so even a 25 watt inverter is potentially dangerous.

 

[PaulRainbow]

Can I suggest that the AC Earth be terminated on the DC Neg Bus, then a single bonding cable taken from the DC Neg Bus to the “water earth” - be it an anode or the hull of a steel boat. This arrangement will ensure the AC supply RCD/RCBO trips, should a fault develop which results in 230v leaking onto the DC system or steel hull. Apologies Paul if you’ve covered this elsewhere within the thread (did check but may have missed it)

Current new build regs state that the AC Earth be connect to water (for want of a better phrase). That's irrespective of whether or not an inverters is fitted, i always mention it in inverter queries as they are often on older boats where this connection would likely not exist.

With a steel hull, if AC live came into contact with the hull something would trip (if the AC Earth was correctly connected to the hull), so no concerns there. Mostly DC systems have a connection to the water, so again, something would trip if a live wire touched exposed DC equipment. If there was no connection to the water i can't think that it would do any harm making one.

If live came into contact with an exposed part of an isolated DC system you wouldn't get a shock from it if you touched it but if you were simultaneously touching something that was earthed the RCD would trip, so you should be OK there too. Great care would need to be taken with isolated DC systems to ensure that engines and/or transmissions that should remain isolated do so. To be safe i would not make any Earth connections to isolated DC systems.

 

[JOHNPEET]

Current new build regs state that the AC Earth be connect to water (for want of a better phrase). That's irrespective of whether or not an inverters is fitted, i always mention it in inverter queries as they are often on older boats where this connection would likely not exist.

With a steel hull, if AC live came into contact with the hull something would trip (if the AC Earth was correctly connected to the hull), so no concerns there. Mostly DC systems have a connection to the water, so again, something would trip if a live wire touched exposed DC equipment. If there was no connection to the water i can't think that it would do any harm making one.

If live came into contact with an exposed part of an isolated DC system you wouldn't get a shock from it if you touched it but if you were simultaneously touching something that was earthed the RCD would trip, so you should be OK there too. Great care would need to be taken with isolated DC systems to ensure that engines and/or transmissions that should remain isolated do so. To be safe i would not make any Earth connections to isolated DC systems.

The research that I undertook during my build led me to the configuration as per my previous comment - AC earth connected to the Neg Bus and a single bonding cable connecting the Neg Bus to the hull. I have a steel hull with isolated DC systems throughout. By connecting the AC earth to the Neg bus, should a fault occur resulting in 230v being present on the DC circuitry, the RCD will trip without relying on any human contact to force to do so. Thus avoiding the small risk of the RCD not operating with the required disconnection time.
Bonding the DC Neg bus to the hull in one location only, protects the hull against corrosion (galvanic?) should a DC fault occur connecting the DC pos to the hull - this will result in a final circuit fuse operating. This arrangement then allows the accessible single hull bond to be disconnected periodically, to allow a continuity test to be carried out between the Neg bus and hull to ensure that the DC circuitry remains isolated from the hull. Thus preventing current flow through the hull.