Marine AC - Why Tie Neutral and Earth?

[Wotname]

Originally Posted by 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?

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"

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

Thanks for posting however all of the information you provided is only pertinent to a grounded neutral AC source. The thread is about a floating AC source.

[Thumbs Up]

Actually lost sleep pondering this last night. A gfci will still provide protection even if the ground wire is not connected because of the earth referenced neutral. But that is not a floating ground system. (And why I got it wrong earlier). I found this statement on Wikipedia: A residual current device can be incorporated into a system to reduce but not eliminate the risks caused by a floating ground.https://en.wikipedia.org/wiki/Floating_ground but it does not explain how.

[Frankly]

Think a lot of what is being lost in this is the prasitic capacitance to the environment (earth, water, conductive surface, whatever). Maybe not a large number but just does not take a lot of current to light up us humans (25 or 30 ma can be lethal if the heart gets in the way). A perfectly isolated/ floating AC system just does not exist in most of the real world. Draw capacitors from your both current carrying conductors to earth and then put your stick figure between a conductor and ground. The troublesome current path should be obvious.


Frankly

As I said before real hazard depend on specific conditions.

[s/v Jedi]

It’s good to see that people are actually starting to think it over and discuss specifics instead of parroting “ must be grounded”

So here are the reasons for having the ground wired to outlets as well as still using gfci outlets and double pole breakers.

If you do not wire the ground conductors to outlets then theoretically it is possible that two appliances with metal housings develop a short to the housing, with one shorting L1 and the other L2. This creates a lethal voltage on two exposed metal surfaces that can electrocute a person.
If the ground wiring is installed, this creates a hard short flipping the breaker.

Someone posted a diagram showing ground faults and a gfci outlet. So here we have a resistance instead of a hard short. The resistance limits current so that a breaker isn’t triggered, but it can potentially still hurt or even kill a person. The way the diagram is drawn, this will never trigger the gfci protection like mentioned in that comment. However, if you have two gfci outlets and ground faults develop in between them, then they trigger when the current exceeds the gfci trigger value. The outlets still protect even though the test buttons don’t work.

The above also suggests to make every outlet a gfci outlet and not use “downstream” normal outlets.

Double pole breakers are needed because both conductors are hot. For US installations, 220V circuits always have double pole breakers for this reason.

I guess everyone knows my wiring diagram by now but I’ll attach it again. This is for US wiring... for EU wiring you simply leave the auto transformers out.

Edit: in the diagram you can see that I simply eliminate the neutral by just not connecting it from the genset nor the 120/240 50A shore power. I simply only take L1 and L2. Where this isn’t possible is with a 120V 30A shore power connection. This is tackled by using L1 and N to power the primary windings of an isolation transformer, then jumpering its output for 1:2 240V and not grounding either output conductor.

[s/v Jedi]

Originally Posted by Thumbs Up

Pretty sure that the European standard and the newest AYBC standards allow floating grounds with proper residual current devices (RCD's). A lot of what has been said already is wrong. It is a contentious subject because the holy grail of boat safety is supposed to be about that green wire being a return path to ground that would trip a breaker in case of a ground fault. There are two definitions to the phrase ground fault though. The first is basically a short circuit that occurs when an energized conductor touches anything that is grounded and hopefully causes a breaker to trip. The second definition is a type of fault in which the unintentional pathway of the straying electrical current flows. It is this second definition that we refer to when talking about RCDs and GFCIs (ground fault circuit interrupters). These devices need no reference to earth ground (as some have alleged). They do not compare voltage (as someone said), they compare current between the two conductors. If there is a difference , the device trips. With a floating system (no ground reference), outlets do not need their ground wire connected. The scary thing about grounded systems is that they are tied to the bonding system, which is tied to the water (through the propshaft/thruhull bonding) If that earth wire inadvertently becomes live in a way that does not trip a breaker, the water around the boat as well as the boat itself become energized. The beauty of the floating system is that this can not happen. The problem with return path to ground logic is that a partial or intermittent short might not trip a breaker but can still transfer enough juice to cause an electrocution or electric shock drowning. The problem with RCD devices is nuisance tripping, and people who bypass them (instead of correcting the fault).

The ABYC is a bit slow but will catch up eventually. I see them more like a set of recommendations for a basic safe system, with more advanced systems like floating power distribution out of their scope.

[Wotname]

Originally Posted by s/v Jedi

..............

The above also suggests to make every outlet a gfci outlet and not use “downstream” normal outlets.

Double pole breakers are needed because both conductors are hot. For US installations, 220V circuits always have double pole breakers for this reason.

..........

OK, I hadn't considered downstream gfci outlets but it's makes sense to do so.

Re double pole breakers - still not sure why they are needed with a single phase floating source - neither conductor is hot except to it's mate.

Of course they are required in the two (or three phase) bonded earth neutral systems.

[s/v Jedi]

Originally Posted by Wotname

OK, I hadn't considered downstream gfci outlets but it's makes sense to do so.

Re double pole breakers - still not sure why they are needed with a single phase floating source - neither conductor is hot except to it's mate.

Of course they are required in the two (or three phase) bonded earth neutral systems.

The reason for single pole breakers is that the neutral is bonded to ground, which they then consider safe. If you want to work on a distribution circuit and you take the power off by flipping it’s breaker, you can still be using power tools etc. powered from another circuit that has that other conductor. This is the main reason for double pole breakers.

[Lake-Effect]

Originally Posted by s/v Jedi

The ABYC is a bit slow but will catch up eventually. I see them more like a set of recommendations for a basic safe system, with more advanced systems like floating power distribution out of their scope.

This is the crux of the issue - safety for the most possible users. A Jedi knows enough to weigh the pros and cons, and to implement a floating AC system with double-pole switches and breakers, the right sort of RCDs, etc. And how to get a surveyor to pass it.

And ABYC isn't a great big binding standards body like NEC, and certainly don't have the budget or mandate to create and test a complete new AC standard for boats. They apply the existing NEC and other "terrestrial" standards to boats, with appropriate marine adaptations (stranded wire, no wire-nuts, "marinized" breakers, reversed hot/neutral warning, ELCI on shorepower in, etc)

Originally Posted by Thumbs Up

Pretty sure that the European standard and the newest AYBC standards allow floating grounds with proper residual current devices (RCD's).

Nobody allows floating grounds.

Current ABYC standards don't allow floating 110 VAC systems.

[Thumbs Up]

Originally Posted by s/v Jedi

The outlets still protect even though the test buttons don’t work.

Here is the thing. The test button on the gfci outlet does still work. I have an inverter powering a single GFCI outlet with no ground wire and the test button works. I looked this up. A plug in GFCI outlet tester will not work (without the ground). The test button on the outlet itself does work.

[Thumbs Up]

Originally Posted by Lake-Effect

Nobody allows floating grounds.

Current ABYC standards don't allow floating 110 VAC systems.

I had it mixed up with bonded vs unbonded systems. Had to give myself a refresher course.

[bdgWesternMass]

Originally Posted by s/v Jedi

It’s good to see that people are actually starting to think it over and discuss specifics instead of parroting “ must be grounded”

So here are the reasons for having the ground wired to outlets as well as still using gfci outlets and double pole breakers.

If you do not wire the ground conductors to outlets then theoretically it is possible that two appliances with metal housings develop a short to the housing, with one shorting L1 and the other L2. This creates a lethal voltage on two exposed metal surfaces that can electrocute a person.
If the ground wiring is installed, this creates a hard short flipping the breaker.

Someone posted a diagram showing ground faults and a gfci outlet. So here we have a resistance instead of a hard short. The resistance limits current so that a breaker isn’t triggered, but it can potentially still hurt or even kill a person. The way the diagram is drawn, this will never trigger the gfci protection like mentioned in that comment. However, if you have two gfci outlets and ground faults develop in between them, then they trigger when the current exceeds the gfci trigger value. The outlets still protect even though the test buttons don’t work.

The above also suggests to make every outlet a gfci outlet and not use “downstream” normal outlets.

Double pole breakers are needed because both conductors are hot. For US installations, 220V circuits always have double pole breakers for this reason.

I guess everyone knows my wiring diagram by now but I’ll attach it again. This is for US wiring... for EU wiring you simply leave the auto transformers out.

Edit: in the diagram you can see that I simply eliminate the neutral by just not connecting it from the genset nor the 120/240 50A shore power. I simply only take L1 and L2. Where this isn’t possible is with a 120V 30A shore power connection. This is tackled by using L1 and N to power the primary windings of an isolation transformer, then jumpering its output for 1:2 240V and not grounding either output conductor.

Thank you for this information and other informative posts.

Would it also be true that in addition to electrical safety issues that galvanic corrosion is simpler to manage with central grounding?

[Thumbs Up]

Originally Posted by Wotname

Of course they are required in the two (or three phase) bonded earth neutral systems.

Is easy to get confused when talking about phases. The correct terminology (for 240v with L1,L2,) is split single phase.

[s/v Jedi]

Originally Posted by Thumbs Up

Here is the thing. The test button on the gfci outlet does still work. I have an inverter powering a single GFCI outlet with no ground wire and the test button works. I looked this up. A plug in GFCI outlet tester will not work (without the ground). The test button on the outlet itself does work.

WTF it -does- work! Or at least the ones you and me have. Diagram attached. It appears the resistor is switched between L and N in such a way the the current through the resistor does not go through the measuring transformer. This is cool!

That said, there must be other (RCD?) devices that use the ground conductor because I’m sure I encountered those in the past.

So GFCI outlets are great to use in floating power distribution systems. I still recommend ground conductors though

[s/v Jedi]

Originally Posted by bdgWesternMass

Thank you for this information and other informative posts.

Would it also be true that in addition to electrical safety issues that galvanic corrosion is simpler to manage with central grounding?

It is completely eliminated. The one worry I have is with engine and genset blocks that are used as negative return path. Also, the anchor windlass. I have seen a 4V potential between a ground plate attached to the hull and the anchor chain while anchored in 12’ deep water. The chain was the very expensive 12mm stainless and it was half eaten away in 2 weeks time. The windlass metal parts must not be connected to battery negative nor to a ground/bonding system aboard.

[bdgWesternMass]

Originally Posted by s/v Jedi

It is completely eliminated.

It seems between that and the safety....

Originally Posted by s/v Jedi

The one worry I have is with engine and genset blocks that are used as negative return path. Also, the anchor windlass. I have seen a 4V potential between a ground plate attached to the hull and the anchor chain while anchored in 12’ deep water. The chain was the very expensive 12mm stainless and it was half eaten away in 2 weeks time. The windlass metal parts must not be connected to battery negative nor to a ground/bonding system aboard.

I'm not advocating that you switch to positive ground but I think the above issue was one of justifications I found for using positive ground on a boat.

Do you have an opinion?