Marine AC - Why Tie Neutral and Earth?

[Thumbs Up]

This image is from the other threadhttps://www.cruisersforum.com/forums...um-109344.html
The protective wire is the outlet ground, third wire, pseudo ground or whatever we are calling it. It could trip a breaker but an imbalance of 30ma would cause it to trip the RCD first.

[s/v Jedi]

Originally Posted by Thumbs Up

I am pasting this from the 2013 thread:

But that was your old system, correct?

It was... but that part is still the same:

In a double outlet, the ground contacts and appliance grounding protect against any fault scenario with a floating power distribution. You don’t even need the outlet ground connected to wiring.

When two outlets are in play, we get the obscure theoretical scenario where two appliances get their metal housing energized with the first from L1 and the second from L2. In this case you achieve full protection by connecting both outlet ground connections to each other.

We can go one step further, where the isolation fault isn’t a hard short but a resistive or capacitive partial that does not trip the breaker. This is where the gfci outlet protects if the current through your body is greater than the gfci trigger rating... i.e. you may feel something when it can’t hurt you but it’ll trip otherwise.

[s/v Jedi]

Originally Posted by boatpoker

A few thousand surveys and I've yet to see a boat with a GI and an isolation transformer.

How many surveys had an isolation transformer? How many of those had two shore power hookups?

[Thumbs Up]

Originally Posted by s/v Jedi

It was... but that part is still the same:

In a double outlet, the ground contacts and appliance grounding protect against any fault scenario with a floating power distribution. You don’t even need the outlet ground connected to wiring.

When two outlets are in play, we get the obscure theoretical scenario where two appliances get their metal housing energized with the first from L1 and the second from L2. In this case you achieve full protection by connecting both outlet ground connections to each other.

We can go one step further, where the isolation fault isn’t a hard short but a resistive or capacitive partial that does not trip the breaker. This is where the gfci outlet protects if the current through your body is greater than the gfci trigger rating... i.e. you may feel something when it can’t hurt you but it’ll trip otherwise.

So these outlets have their grounds connected together, but if I understand correctly they are also tied to the boats other grounds as well as shore ground (with the 50 amp plugged in). They should instead tie into your center tap (N on your autotransformers).

[s/v Jedi]

Originally Posted by Thumbs Up

It would still trip in this case without the ground wire connected to anything. Introducing earth ground to this connection does nothing except create the possibility of an additional safety hazard in the water. If the the outlet grounds were instead connected to the auto transformer neutrals a fault to an appliance case would trip the RCD breaker. The way you have it a fault to an appliance case does nothing except connect one hot wire to the water.

? There is no connection to the water... I did write it would trip without ground wire connected, why do you repeat that?

In case of the 50A shore power connected, you can’t connect the neutral output of an auto transformer to ground. If you do, you get an equalizing current over shore ground. You can’t even connect the neutral outputs of the two auto transformers together because even with the exact same brand and model, small differences will exist and create phantom current paths.

If you have an ABYC wired boat that has an appliance which develops an isolation fault, it does the exact same thing: L gets connected to ground and thus the water until the breaker trips.

[s/v Jedi]

Originally Posted by Thumbs Up

This image is from the other threadhttps://www.cruisersforum.com/forums...um-109344.html
The protective wire is the outlet ground, third wire, pseudo ground or whatever we are calling it. It could trip a breaker but an imbalance of 30ma would cause it to trip the RCD first.

Exactly. So that diagram shows that isolation is the best, just what I have been promoting all these years.

The second scenario is for non isolated power and it demonstrates the need for ground leak/rcd/gfci devices to improve safety.

This all supports my case, why do you think different?

[s/v Jedi]

Originally Posted by Thumbs Up

So these outlets have their grounds connected together, but if I understand correctly they are also tied to the boats other grounds as well as shore ground (with the 50 amp plugged in). They should instead tie into your center tap (N on your autotransformers).

No.... they only connect to the boat AC ground busbar. There is no connection with DC negative nor with any ground plates, engine blocks, underwater metals etc.

Only when shore 50A is connected, it becomes a non-isolated system just like every boat without an isolation transformer. Shore neutral is grounded, but I don’t use it: when you zoom in to the EMS/surge suppressor you will see shore neutral go in, but not come out. Only L1, L2 and ground (via galvanic isolator) are connected. Nobody forces you to use shore neutral... if you want 120V from shore you have to, but I only use 240V. The inverter/chargers are 240V.

[Thumbs Up]

[QUOTE=s/v Jedi;3403477
So the ground wire (green/yellow, earth, bare copper) on the outlets all go to the ground busbar as shown in my diagram. This is where the ground wires from transformers, inverter/chargers, boat-side of galvanic isolator and isolation transformer etc. go. It is not connected to DC negative and not to AC Neutral. It’s only job is to connect all external metal surfaces of appliances together.
[/QUOTE]

Originally Posted by s/v Jedi

Exactly. So that diagram shows that isolation is the best, just what I have been promoting all these years.

The second scenario is for non isolated power and it demonstrates the need for ground leak/rcd/gfci devices to improve safety.

This all supports my case, why do you think different?

Because (according to the above quote) you have your outlet safety grounds tied into 50A shore ground (according to your diagram) and also, I am assuming, the anti corrosion bonding system on your boat (thus the water). Also shore ground is connected to AC shore power neutral (via the 50A power pedestal's source)

EDIT: I see that you have stated not to underwater metals

[s/v Jedi]

Originally Posted by Thumbs Up

Because (according to the above quote) you have your outlet safety grounds tied into 50A shore ground (according to your diagram) and also, I am assuming, the anti corrosion bonding system on your boat (thus the water). Also shore ground is connected to AC shore power neutral (via the 50A power pedestal's source)

You have to snap out of that... I have written multiple times that when connected to 50A shore power, which is almost never, then my system is NOT an isolated power distribution anymore. It’s simply a 240V system with just a galvanic isolator.

Also, I wrote that I do NOT connect my AC ground to any other anti corrosion or bonding systems. Your assumption is wrong and thus irrelevant.

[Thumbs Up]

Originally Posted by s/v Jedi

In case of the 50A shore power connected, you can’t connect the neutral output of an auto transformer to ground. If you do, you get an equalizing current over shore ground. You can’t even connect the neutral outputs of the two auto transformers together because even with the exact same brand and model, small differences will exist and create phantom current paths.

I am not saying to connect transformer neutral output to ground, I am saying connect it only to the outlet grounds. If you have each transformer supplying separate circuits, connect the outlet grounds to their respective transformer neutrals. You should not have your outlet grounds connected any where else.

[Thumbs Up]

Originally Posted by s/v Jedi

You have to snap out of that... I have written multiple times that when connected to 50A shore power, which is almost never, then my system is NOT an isolated power distribution anymore. It’s simply a 240V system with just a galvanic isolator.

Also, I wrote that I do NOT connect my AC ground to any other anti corrosion or bonding systems. Your assumption is wrong and thus irrelevant.

Sorry, I guess you didn't see my edit. Your auto transformers should still be able to isolate the supply. Maybe not?

2.4. Ground Relay
In most energy systems for residential or mobile use a TT configuration is used, which means the Neutral of the AC system is
grounded. This is to ensure the GFCI breaker will trip in case there is an earth failure (The connection N/PE will ensure a current
will flow in the secondary circuitry which is detected by the GFCI).
As an autotransformer is also able in some systems to “create” a neutral different from the incoming neutral, a ground relay is
included in the unit. This relay can be controlled by a Multi/Quattro (by disabling the internal ground relay in the inverter/charger
through VE Config or Victron Connect and interconnecting the “ground relay” terminal block in Multi/Quattro and Earth terminal
block in Autotransformer by Positive and Negative conductors. In some of the diagram examples in Section 2.4.1 through 2.4.3 it
is mentioned when it is possible to use the ground relay.https://www.victronenergy.com/upload...sformer-en.pdf

[s/v Jedi]

I know this gets confusing so let me make this a bit clearer:

A floating power distribution can only be realized when you use a genset, inverter or shore power in combination with an isolation transformer. A floating system doesn’t mean that the shore ground wire is isolated... even though that is the primary reason for an isolation transformer... it means that there is no galvanic connection between shore power and boat power.

All that the shore power does is create a magnetic field using the primary winding of the isolation transformer.

When we have a common 50A shore power in the US, you get 4 conductors, each 6AWG. You get ground/earth, L1, L2 and neutral. At the distribution transformer ashore, the neutral is grounded. L1 and L2 are both hot, have 240V between them and each has 120V to neutral. L1 and L2 are a secondary winding on the distribution transformer, with neutral being a center tap of that same winding.

The very best thing you can do with that 50A shore power when it comes aboard, is to put it into a so-called EMS which stands for Energy Management System. This isn’t just a breaker... it is a contactor (big relay) with a microcontroller deciding to open or close that contactor (it does have a manual override). This is much like the transfer switch on line input of a Multiplus. The EMS checks voltage range, line frequency, current, transient spikes etc. and only when it determines that the power is good, it will close the contactor and pass power on.

With that done, the best thing to do is connect that output to an isolation transformer. You connect L1 and L2 to it’s primary winding and ground to the transformer shore-side ground terminal. You don’t connect the neutral... you simply don’t need it, but you also can’t because it’s connected to shore ground which you are eliminating from the boat.
On the output you get a couple of secondary windings which are 120V, plus you get a terminal for boat ground which is isolated from shore ground (ignore people telling you to interconnect those two... it’s an isolation transformer). The secondary windings are jumpered in series for 240V service and if that’s all you want then you can use that jumper as your new neutral. You can even connect it to boat ground if you want to adhere to ABYC recommendations but this exposes your boat to corrosion problems, increase risk for swimmers etc.

There is a reason for not doing this isolation transformer: you need a 12kW transformer which is huge and expensive. If you don’t want that then you can opt for a galvanic isolator, which is what I did. Now you don’t get a floating power distribution so you increase risk and need more protection mechanisms, like grounded outlets, gfci outlets as well as rcd breakers.

Of course when you have a floating power distribution, you can still install grounded gfci outlets and rcd breakers. These improve safety beyond what is required but theoretically possible fault scenarios. The advantage of doing this... like I did.. is that you can go back to a polarized non floating system without changing much... in my case I have two shore power systems, one isolated and able to accept 120V as well as 240V and one not floating.

There are many reasons to have a floating power distribution but for a boat it’s mainly optimal safety for the boat as well as the crew. Shore power is much more difficult but for many boats hardly ever used. We are in a “foreign” marina right now but don’t have shore power connected... why would we pay for that when we get all the power we need for free from our solar panels and inverters? If we would use shore power here, we would use the 3.6kW isolation transformer, not the 50A one.

[s/v Jedi]

Originally Posted by Thumbs Up

I am not saying to connect transformer neutral output to ground, I am saying connect it only to the outlet grounds. If you have each transformer supplying separate circuits, connect the outlet grounds to their respective transformer neutrals. You should not have your outlet grounds connected any where else.

I’m sorry but not even ABYC recommends connecting neutral to the ground terminals of outlets. The ground terminals of outlets must be connected to the AC ground aboard, which can be earth (shore power) or chassis ground (floating isolated).

[s/v Jedi]

Originally Posted by Thumbs Up

Sorry, I guess you didn't see my edit. Your auto transformers should still be able to isolate the supply. Maybe not?

No, they don’t. There is no isolation in an auto transformer because it’s just one single winding with center tap.

The grounding relay in the auto transformer is used in combination with a Multiplus when using a 230/240V unit to create a split phase 120/240 service. The inverter can’t ground the neutral because it doesn’t have the neutral... but it can signal the auto transformer to do this.
This only happens in inverter mode because that creates a power source where the neutral needs to be grounded for grounded-neutral systems. When the genset or shore power is available, this relay is switched off before the input transfer switch forwards that power.

For floating systems the neutral isn’t grounded at all.

[Thumbs Up]

Originally Posted by s/v Jedi

I know this gets confusing so let me make this a bit clearer:

A floating power distribution can only be realized when you use a genset, inverter or shore power in combination with an isolation transformer. A floating system doesn’t mean that the shore ground wire is isolated... even though that is the primary reason for an isolation transformer... it means that there is no galvanic connection between shore power and boat power.

All that the shore power does is create a magnetic field using the primary winding of the isolation transformer.

When we have a common 50A shore power in the US, you get 4 conductors, each 6AWG. You get ground/earth, L1, L2 and neutral. At the distribution transformer ashore, the neutral is grounded. L1 and L2 are both hot, have 240V between them and each has 120V to neutral. L1 and L2 are a secondary winding on the distribution transformer, with neutral being a center tap of that same winding.

The very best thing you can do with that 50A shore power when it comes aboard, is to put it into a so-called EMS which stands for Energy Management System. This isn’t just a breaker... it is a contactor (big relay) with a microcontroller deciding to open or close that contactor (it does have a manual override). This is much like the transfer switch on line input of a Multiplus. The EMS checks voltage range, line frequency, current, transient spikes etc. and only when it determines that the power is good, it will close the contactor and pass power on.

With that done, the best thing to do is connect that output to an isolation transformer. You connect L1 and L2 to it’s primary winding and ground to the transformer shore-side ground terminal. You don’t connect the neutral... you simply don’t need it, but you also can’t because it’s connected to shore ground which you are eliminating from the boat.
On the output you get a couple of secondary windings which are 120V, plus you get a terminal for boat ground which is isolated from shore ground (ignore people telling you to interconnect those two... it’s an isolation transformer). The secondary windings are jumpered in series for 240V service and if that’s all you want then you can use that jumper as your new neutral. You can even connect it to boat ground if you want to adhere to ABYC recommendations but this exposes your boat to corrosion problems, increase risk for swimmers etc.

There is a reason for not doing this isolation transformer: you need a 12kW transformer which is huge and expensive. If you don’t want that then you can opt for a galvanic isolator, which is what I did. Now you don’t get a floating power distribution so you increase risk and need more protection mechanisms, like grounded outlets, gfci outlets as well as rcd breakers.

Of course when you have a floating power distribution, you can still install grounded gfci outlets and rcd breakers. These improve safety beyond what is required but theoretically possible fault scenarios. The advantage of doing this... like I did.. is that you can go back to a polarized non floating system without changing much... in my case I have two shore power systems, one isolated and able to accept 120V as well as 240V and one not floating.

There are many reasons to have a floating power distribution but for a boat it’s mainly optimal safety for the boat as well as the crew. Shore power is much more difficult but for many boats hardly ever used. We are in a “foreign” marina right now but don’t have shore power connected... why would we pay for that when we get all the power we need for free from our solar panels and inverters? If we would use shore power here, we would use the 3.6kW isolation transformer, not the 50A one.

I knew all of this except for the part about the EMS.
.

Originally Posted by s/v Jedi

No, they don’t. There is no isolation in an auto transformer because it’s just one single winding with center tap.

The grounding relay in the auto transformer is used in combination with a Multiplus when using a 230/240V unit to create a split phase 120/240 service. The inverter can’t ground the neutral because it doesn’t have the neutral... but it can signal the auto transformer to do this.
This only happens in inverter mode because that creates a power source where the neutral needs to be grounded for grounded-neutral systems. When the genset or shore power is available, this relay is switched off before the input transfer switch forwards that power.
For floating systems the neutral isn’t grounded at all.

I admit to being out of my league on autotransformers. I thought it was more like an isolation transformer (I do understand what it is for just not how it works)

Originally Posted by s/v Jedi

I’m sorry but not even ABYC recommends connecting neutral to the ground terminals of outlets. The ground terminals of outlets must be connected to the AC ground aboard, which can be earth (shore power) or chassis ground (floating isolated).

I thought that ABYC doesn't recommend isolated power supply (IT) systems period. Neutral is normally bonded to ground at the source. With an IT supply, the source is the output of the transformer. It would seem normal to connect the outlet safety ground wires here, before the output breaker. Since there is no real neutral then either output would do, say L2. If the output breaker was also an RCD then that connection would act as a fault protective wire, because current on it would create an imbalance and trip the RCD. If it was only connected to the chassis of the transformer it would not have the protective feature. This is what I was studying before I decided to try to critique your system.

It started as more of a question because I was thinking about where to tie the outlet grounds. I was looking for an example when I found the other thread. Goboatingnow described it this way:

The solutions are

( a) re establish ground referenced output and earth wire and rely on breakers and RCDs. Hence the IT provides no security as most shock hazards are fault through human to ground

(B) establish a fault protective wire , connecting one live of the IT to appliance case with an RCD then ahead of the common protective wire and IT secondary.

Option B is what I am referring to.
So without getting wrapped up on how to apply this to your setup, Jedi, the question that I was looking to verify (and partially did from what goboatingnow had wrote) is: Is this a good way to do it? (and if not why, and what is the safest possible option)
My other takeaway, as an alternative was that if you happened to have a center tap, that you could lead the outlet grounds there.
We have established that dedicated GFCI outlets greatly improve the safety and would be considered best practice. The question (once again to be clear) is: Where is the best place to lead that third wire (the outlet grounds) on a fully isolated IT (floating) distribution system. Your opinion is appreciated. There doesn't seem to be a standard for this type of system on a small yacht and we are trying learn what we can because once we deviate from standard practice, any accident would implicate us.
The question is directed at Jedi but of course want to hear what the OP thinks and anyone else who is following this. (and goboatingnow and Steve DAntonio)