Marine AC - Why Tie Neutral and Earth?

[Lake-Effect]

Originally Posted by boatpoker

The OP said ... "Can someone explain the logic of using a tied neutral/earth AC system on a sailing boat?"

the OP also said

I understand why power.html" target="_blank">shore-IRJDSUNE9932123321222xxeww-power uses a Neutral / Earth connection but why do this with an onboard AC supply?

... so, to me anyway, it was apparent that they were asking about floating or not floating onboard AC sources.

[boatpoker]

Originally Posted by Lake-Effect

the OP also said

I understand why power.html" target="_blank">shore-IRJDSUNE9932123321222xxeww-power uses a Neutral / Earth connection but why do this with an onboard AC supply?

... so, to me anyway, it was apparent that they were asking about floating or not floating onboard AC sources.

I should know better than to get involved in these conversations.
This topic is beyond explanation on a public forum .... Need confirmation ? Look at some of the responses.

[Lake-Effect]

Originally Posted by boatpoker

I should know better than to get involved in these conversations.
This topic is beyond explanation on a public forum .... Need confirmation ? Look at some of the responses.

c'mon,BP... most of us here, including the OP, seem to get that you don't connect shorepower neutral and ground aboard the boat (shorepower neutral is already connected to ground ashore)

They were asking about onboard AC sources (eg generators, inverters, isolation transformers) and why these should have to have their neutral connected to ground.

Wotname, please confirm.

[Wotname]

Originally Posted by Lake-Effect

c'mon,BP... most of us here, including the OP, seem to get that you don't connect shorepower neutral and ground aboard the boat (shorepower neutral is already connected to ground ashore)

They were asking about onboard AC sources (eg generators, inverters, isolation transformers) and why these should have to have their neutral connected to ground.

Wotname, please confirm.

Confirmed!

I am not interested about shore power, I already know why the N and E are bonded when using shore power.

Is an apology needed because I didn't explain the question clearly enough??? It seemed to me it was obvious I was asking about AC sources generated on board.

Presumably the question is now clear and if any one wants to reconsider their previous posts, it would be most welcome. We can discuss shore power considerations later when the thread drift kicks in.

FWIW, I have great respect for the electrical knowledge the principle posters (so far) and I do welcome your input. I don't always agree with you at all times but we all know that electricity follows electrical principles and not our opinions.

To repeat, it seems electrically safer to me for onboard generated AC sources to have a fully floating output, i.e no earth conductor, no 'ground', just two conductors (let's call them A & N). However it isn't done this way (AFAIK) so why isn't it when it appears to be a safer arrangement?

[boatpoker]

Originally Posted by Wotname

it seems electrically safer to me for onboard generated AC sources to have a fully floating output, i.e no earth conductor, no 'ground', just two conductors (let's call them A & N). However it isn't done this way (AFAIK) so why isn't it when it appears to be a safer arrangement?

I rest my case.

[Wotname]

Originally Posted by Dsanduril

Here are a couple of interesting articles on the subject:

https://www.benderinc.com/know-how/t...loating-system

https://www.lsp-international.com/po...grid%20system.
https://www.eaton.com/content/dam/ea...ap083005en.pdf

Note that there are places in the current code world where floating systems are preferred (moist/wet environments being one of them), and there is reduced risk of things like fire in a properly configured floating system because the fault currents are not nearly so high.

I don't think anyone here is advocating that it is safe to just go out and float your boat's AC system, but it is a topic worthy of discussion and maybe a chance to get standards to catch up with the modern world.

Thanks for the links, I haven't had a chance to read yet but they are now on my reading list!

It looks like parts of the code world is thinking along similar lines as myself (?)
BTW, I concur with your last paragraph.

[dkenny64]

just my 2 cents...


if you're are talking about on board AC sources.
then its 120v or 240v.. but how and what do these mean..
in the US 120v is between 1 hot and neutral. 240v is between 2 hots..no neutral or ground..think about it... if its a generator, that outputs 120v or 240v..the 120v is 2 windings.. the 240v is 2 windings but tied in series not parallel( for 120v).. but what is GND...its the case of the generator...incase either hot is shorted to generator case..safety.. if the center tap of the 240v isn't tied to case(GND). then the whole system is floating..so touching an ac hot to DC GND means nothing( no current path)
unless I'm wrong this is what an isolation transformer provides. AC is floating..
-dkenny64

[Wotname]

Originally Posted by boatpoker

I rest my case.

Well then you haven't made your case very clear.

Let me make is easy for you.

Is it -

1. Fully floating is safer
or
2. A tied N&E with a AC ground is safer
or
3. Wottie doesn't have sufficient electrical knowledge to understand.

If it is 1 or 2, then please explain your reasons in electrical terms.
If it is 3, then you are either arrogant or have never read / understood thousands of my previous posts in the electrical threads.

I very much doubt you can confuse me regarding electrical principles but you may be able to demonstrate some understanding that I don't yet have. It is even possible I have a greater understanding than you but unless you engage, you will never know.

Or perhaps your case is something totally different.... (???)

[dkenny64]

hum
no mention for using GFCI for the AC.. of you want safe...use them..
gnd or not..they only check for the delta between hot and neutral...NOT GND
so they work on 2 wire systems just as well as 3 wire..
yes the cheap wall tester will fail..


-dkenny64

[Frankly]

First off shipboard inverter/ inverter generator powered AC system and generator systems are different in significant ways. A 5 or 10 KW generator will typicaly deliver the fault current required to quickly clear a ground fault and trip the supplying breaker (there is energy in that thar rotating field). An inverter will usually trip off very quickly as a means of self protection of the solid state components.

An unmonitored ungrounded electrical system may be safer until the first ground fault has ocurred. Now you probably have a more hazardous situation if not discovered. Double insulation, ground fault receptacles, RCCB (GFI on steroids) are all making electrical systems safer but sometimes with reduced reliability. Combining the above in a typical system with the neutral and ground connected at the source is still probably safest.

I contend in most scenarios the much maligned Honda inverter generator can be operated with the neutral and ground connected or isolated with little difference in electrical safety.

Recently installed a 10 KW rooftop solar system on my home (grounded metal roof). The string voltage is 400 volts measured positive to negative, either end of the string measured to the roof less than 5 volts (even wet down with a garden hose). Feeling pretty safe eh. Ground fault in one of those collectors or connect the non galvanic iolated grid tie inverter, pretty deadly situation now exists.

Like most complex things in life, it depends.


Frankly

[Dsanduril]

Originally Posted by Frankly

An unmonitored... ungrounded electrical system may be safer until the first ground fault has occurred. Now you probably have a more hazardous situation if not discovered....

This is pretty much how the literature describes the prospect of ungrounded electrical systems - where there is lots of ground/other grounded components in the vicinity. It's a different story for a fully-isolated and independent system, and that is really what the OP is asking.

You use an example of a 400V DC system on your metal roof, which could be potentially fatal if the wrong conditions develop. And yet there are literally hundreds of thousands of Tesla automobiles running around with similar DC voltages (350-375) and even more Prii and these are all completely ungrounded, isolated systems. They're not AC (as the OP questioned) but they provide an example of ungrounded low voltage systems (in IEC terms low < 1000V) that are demonstrably safe, even when a person forms the bridge from ground to vehicle. Will there be accidents that cause electrocution? Eventually I'm sure there will be, and then increased safety standards, ....

[Wotname]

Several posters keep referring to 'ground' faults but exactly what is 'ground' fault in a two wire floating output?

How can a 'ground' fault exist if the potential difference (say 120V AC) only exists between the two conductors. AFAIK, there can't be any potential difference between either conductor (A or N) and any other surface.

The only possible time an operator could experience a risky potential difference could occur (AFAIK) is IF a fault (ie conductive path) exists between one conductor (say A) and a conductive case of an load and at the same time another similar fault occurs in another similar load between the other conductor (i.e. N) and if one touches both the conductive cases at the same time.

Put another way, in a fully floating two wire output, the only electrical risk occurs when one's body becomes part of the circuit between the two wires. The ground or earth or engine or hull or sea water or the man on the moon can never be part of the circuit (unless two separate faults (one on each wire) occur on two different objects , and your body connects the two seperate objects.

No????

[Wotname]

Originally Posted by dkenny64

hum
no mention for using GFCI for the AC.. of you want safe...use them..
gnd or not..they only check for the delta between hot and neutral...NOT GND
so they work on 2 wire systems just as well as 3 wire..
yes the cheap wall tester will fail..


-dkenny64

They work ONLY if one of the source wires (i.e N) is tied to 'ground'. In a fully floating (2 wire) output neither wire is connected to anything anywhere except the load.

[mitiempo]

Originally Posted by Wotname

Several posters keep referring to 'ground' faults but exactly what is 'ground' fault in a two wire floating output?

How can a 'ground' fault exist if the potential difference (say 120V AC) only exists between the two conductors. AFAIK, there can't be any potential difference between either conductor (A or N) and any other surface.

I assume you are referring to a GFCI without a ground connection - eg only hot and neutral. In this case a "ground fault" is when there is 5 millivolts or more difference between hot and neutral.

It is a ground fault because the user either becomes the grounded conductor or there is leakage to another item - moisture for example - from either the hot or neutral.

GFCIs work just fine without a ground connection.

[kish]

A boat with AC power will have many of the same electrical items as a house on land. There is no difference.

Electrons are electrons in both environments!
Similar standards must apply in both instances.

Check out
Why Do We BOND Neutral & Ground in ELECTRICAL SERVICE PANELS?

https://www.youtube.com/watch?v=_XM6rXjv0vc

Additionally a hot and neutral 2 wire system on board without a ground wire is very problematic and dangerous. .
If there is a wiring fault on board, it can cause current leakage into the water, resulting in a "hot" marina. The fault may be insufficient to cause an overcurrent trip, but:
Current in the water will find a path back to earth using the zincs and underwater metalwork of neighboring boats, who are correctly wired,
A ground wire on board will route this leakage directly back to the marina pedestal ground, saving zincs and shafts from damage

This current in the water is recognized as a Hazard for Electric Shock Drowning (ESD)

"Electric shock drowning carries an especially dangerous risk in marinas or near boat docks. Electrocution in water occurs when faulty wiring on a boat or a dock causes an electrical current to pass through the water"

https://www.youtube.com/watch?v=asm1SxwnZvU

From the National Fire Protection Association
https://www.nfpa.org/Public-Educatio...y-around-water


A Little Knowledge Is A Dangerous Thing
Alexander Pope, 1709