Grounding an inverter

[DotDun]

Originally Posted by rwidman

Dude! Being electrocuted is the same worldwide.

BTW: The inverter is made in China.

Do explain how the OP is in danger of being electrocuted.

The problem is you can't. Without a grounded source, the grounding conductor is useless. A floating source is not dangerous.

[billknny]

Originally Posted by zboss

Let’s simplify this... what is the majority of grounding situations for the majority of inverters on boats? Where do you run the ground to... if read a few inverter manuals and they generally say run to the engine block but a few just have a diagram with a grounding symbol and no clear instruction on where to run the ground.

The problem is that there is not a simple answer that applies to all boats.

Grounding, safety grounding, bonding, and DC negative can be wired and interconnected in different ways, all of which work, but you have to know how they are wired before you make a decision.

Portable inverters are also different than permanently mounted ones.

There is a reason that grounding topics take up many pages of any good book on marine electrics. If someone gives you a simple answer without understand how your boat is wired it MIGHT be right for your boat, or not--even if it is right for someone else's.

For example, on my boat, which is designed for a floating DC negative, interconnecting the DC negative and the AC safety ground would be a galvanic corrosion disaster. Yet most boats actually have such a connection and it is fine.

In most cases someone who gives a simple, one size fits all answer for grounding on a boat might be giving you an exactly correct answer for their boat, but it might be completely wrong for yours.

Getting it wrong can lead to VERY rapid stray current corrosion of underwater metals, or electrocution hazards in ways that aren't obvious.

[a64pilot]

Originally Posted by billknny

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For example, on my boat, which is designed for a floating DC negative, interconnecting the DC negative and the AC safety ground would be a galvanic corrosion disaster. Yet most boats actually have such a connection and it is fine.

I am under the understanding that connecting the two can lead to corrosion in almost any Boat on its external metals, and this is the reason for an isolation transformer, to disconnect the AC ground, and that if you inadvertently connect the AC and DC grounds together you can have voltage leak back to DC and set up corrosion.

[jeepbluetj]

Originally Posted by billknny

...

By your logic it would not be possible to be shocked by holding the hot wire output of a 220V inverter while standing in a wet bilge. Do NOT do this experiment at home!

Her logic is correct. A DC example: If I hooked up 20 12v batteries in series, hooked the negative to nothing, stand in my bilge full of salt water, and clamp my finger to the positive terminal - I'd be fine except for the pain of the clamp on my finger. Soon as I touch the negative with my other hand or connect it to part of the boat I'm toasty.

AC is the same way if it's not ground referenced - like an inverter or a generator that doesn't connect the safety ground to anything.

I think the confusion about safety grounds because all of our shore power (in a house, on your boat, even with a mouse) IS ground-referenced. At some point the grounding electrode(planet earth) is connected to the equipment grounding conductor(the green wire in the US) and it's connected to the neutral at the source. Therefore hot has the potential of whatever it's voltage is to all grounded things including dirt, the lake, the ocean, your faucets, the dryer, etc.. Conduct from the hot to any of those, zappers it is or you pop the GFI.

[CharlieJ]

From ISO 13297-20015 (The European Standard for AC systems):

4.8 The neutral conductor shall be grounded (earthed) only at the source of power, i.e. at the onboard generator, the secondary of the isolation or polarization transformer, or the shore-power connection. The shore-power neutral shall be grounded through the shore-power cable and shall not be grounded on board the craft.

From ABYC E-11 AC and DC Electrical Systems in Boats
11.5.3.2Grounded Neutral-A grounded neutral system is required. The neutral for AC power sources shall be grounded only at the following points:
11.5.3.2.1The shore power neutralis grounded through the shore power cable and shall not be grounded onboard the boat.
11.5.3.2.2The secondary neutral of an isolation transformer or polarization transformer shall be grounded at thesecondary of an isolation or polarization transformer(seeEXCEPTIONand DIAGRAM 5,DIAGRAM 6, DIAGRAM 7,DIAGRAM 8,DIAGRAM 9,and DIAGRAM 10).11.5.3.2.3The generator neutral shall be grounded at the generator(seeEXCEPTION and DIAGRAM 2or DIAGRAM 4).

By the way, the ISO document has required a full vessel RCD with 30mA/100mS trip for many years. ABYC has required it for about five years.

The Honda generator with an unbonded N > G connection is an accident waiting to happen.

The safety ground (green) wire is the holy grail of keeping people safe. The rest is just noise.

[billknny]

Originally Posted by a64pilot

I am under the understanding that connecting the two can lead to corrosion in almost any Boat on its external metals, and this is the reason for an isolation transformer, to disconnect the AC ground, and that if you inadvertently connect the AC and DC grounds together you can have voltage leak back to DC and set up corrosion.

Well...

Yes and no...

The corrosion you are referring to only happens when plugged in at a marina. An isolation transformer is the gold standard for preventing it, but a "zinc saver" installed to block DC voltages in the AC safety wire ground will stop it as well.

An isolation transformer lets you have a AC safety ground separate from the shore power ground, but you STILL NEED A SAFETY GROUND! You can not disconnect the AC safety ground on the boat and have a safe system. If you have done that on your boat, you need to UNDO it as soon as possible.

There are pluses and minus about connecting the DC negative to the boat's ground system. There are good boats that do it either way. People will make long and impassioned arguments about one vs the other... but both work if maintained well. This is obvious to me because I have owned a 40year old boat where they were connected, and I currently have a 20 year old boat where they are not. Neither boat had stray current corrosion problems.

All this is detailed in any good marine electric book.

[billknny]

Originally Posted by CharlieJ

From ISO 13297-20015 (The European Standard for AC systems):


From ABYC E-11 AC and DC Electrical Systems in Boats
11.5.3.2Grounded Neutral-A grounded neutral system is required. The neutral for AC power sources shall be grounded only at the following points:
11.5.3.2.1The shore power neutralis grounded through the shore power cable and shall not be grounded onboard the boat.
11.5.3.2.2The secondary neutral of an isolation transformer or polarization transformer shall be grounded at thesecondary of an isolation or polarization transformer(seeEXCEPTIONand DIAGRAM 5,DIAGRAM 6, DIAGRAM 7,DIAGRAM 8,DIAGRAM 9,and DIAGRAM 10).11.5.3.2.3The generator neutral shall be grounded at the generator(seeEXCEPTION and DIAGRAM 2or DIAGRAM 4).

By the way, the ISO document has required a full vessel RCD with 30mA/100mS trip for many years. ABYC has required it for about five years.

The Honda generator with an unbonded N > G connection is an accident waiting to happen.

The safety ground (green) wire is the holy grail of keeping people safe. The rest is just noise.

LIKE HE SAID!

[DotDun]

Originally Posted by CharlieJ

The Honda generator with an unbonded N > G connection is an accident waiting to happen.

Do explain what accident you are imaging can happen.

[a64pilot]

Originally Posted by DotDun

Do explain what accident you are imaging can happen.

What comes to my mind is that the Honda can short internally, making the chassis “hot” if the chassis were connected to ground, this would of course make it go to direct ground and pop a CB or other overload device, but as the chassis is not connected to ground it is simply hot.
You touch it, and you could provide the ground, I say could cause assuming a clean dry fiberglass boat, maybe not.

However I agree in principle that the ungrounded Honda could be a safety issue

[billknny]

Originally Posted by a64pilot

You touch it, and you could provide the ground, I say could cause assuming a clean dry fiberglass boat, maybe not.

"Assuming a clean dry fiberglass boat"

My boat is usually clean... but assuming it to be dry as part of an electrical safety plan seems... well... a bit at odds with it being a boat!

[a64pilot]

Originally Posted by billknny

"Assuming a clean dry fiberglass boat"



My boat is usually clean... but assuming it to be dry as part of an electrical safety plan seems... well... a bit at odds with it being a boat!

I just threw that out there, cause obviously a squirrel can run down a high voltage line with no problem, but once in awhile you find a fried one, assumption is it bridged the high voltage with a ground somehow.
However the only safety thing I can come up with is if the chassis gets hot, cause nobody grounds these things, nobody in RV’s, construction etc.
Military when we set up the 60KW generators, we drove a ground rod in and connected it to the trailer, but I have not seen anyone else ground a portable generator, ever.

[DotDun]

Originally Posted by a64pilot

What comes to my mind is that the Honda can short internally, making the chassis “hot” if the chassis were connected to ground, this would of course make it go to direct ground and pop a CB or other overload device, but as the chassis is not connected to ground it is simply hot.
You touch it, and you could provide the ground, I say could cause assuming a clean dry fiberglass boat, maybe not.

However I agree in principle that the ungrounded Honda could be a safety issue

What you are describing is a failure mode of a grounded source. With an un-grounded source, you can touch either side without danger. In the OP's case, he can put one side of the AC from his inverter in his mouth, dance around the deck barefoot in his tights-whiteys touching mast, stanchions, he can even jump in the water, and not get hurt.

Most in this thread fail to understand why commercial power is grounded and the dangers associated with a grounded source system, they simply accept the fact that is the way it's done. A grounding conductor is not required if the source is un-grounded. A grounding conductor in a grounded source system delivers (arguably) comparable safety to an un-grounded source system (which has no grounding conductor).

One has to think about the path from/to the source to understand. The less number of paths, the less danger.

To be clear:
Grounded source = system where neutral is connected to ground at the source
Grounding conductor = green/yellow safety wire connected to ground at the source

[billknny]

Originally Posted by a64pilot

I just threw that out there, cause obviously a squirrel can run down a high voltage line with no problem, but once in awhile you find a fried one, assumption is it bridged the high voltage with a ground somehow.
However the only safety thing I can come up with is if the chassis gets hot, cause nobody grounds these things, nobody in RV’s, construction etc.
Military when we set up the 60KW generators, we drove a ground rod in and connected it to the trailer, but I have not seen anyone else ground a portable generator, ever.

On any generator the rule is that the safety ground is run back to the generator (the source of the power) where it and the neutral become one. This gives a path for current to take if there is a short between the hot wire and the case of the device being used other than the body of the user!

I assume that is what happens on any properly designed portable generator. In which case, as far as I can see, they are functionally the same as a fixed mount generator.

So I'm with you... I don't see the special hazard that was suggested for the portable model. Maybe the poster of that comment can elaborate on what he was thinking...

[smac999]

the cheaper inverters are floating grounds. connecting the AC ground to neutral as you should have, will likely just blow it up. if it doesn't have this bond. it should be repalced with a marine rated one that does. the pass through ones will bond and un bond automatically when you have shore power or not.

[transmitterdan]

Boy there is a lot of confusion in this thread. Under ABYC standards US boats must tie the safety ground to the neutral at the source. One reason ABYC requires neutral and safety ground connected at the source is so GFCI outlets will work. Also, the little outlet testers won't work without that connection. In most of the rest of the world this is not required.

Many "cheap" inverters output a balanced output and therefore cannot connect the neutral to the case or DC negative bus without shorting out 1/2 of the inverter. These inverters have no "neutral". So they cannot be used in an ABYC compliant boat. My guess is the OP has such an inverter since the safety ground is not connected to anything.

The simple truth is these cheap inverters often cause hum and there isn't a whole lot that can be done about it.