Isolation Transformer Neutral Ground Connections

[twistedtree]

I’ve got a dinosaur
Xantrex Freedom Marine 25
2500 Watts
130 Amp Charger
Model: 81-2511-12(202)
SN: 281071
Date: 1999

It doesn't look like the bonding relay can be disabled. Perhaps there is a setting via the Link 1000? An inverter upgrade to a sine wave model with a controllable bonding relay could be a good investment as part of this projet.

 

[sunchaser]

For something that is so simple in concept, it can be very difficult to implement it correctly since there are so many ways things can be powered between multiple shore cords, generator(s), and inverters.

We could never quite figure out the optimum wiring around the inverter so when plugging into GFIC dock power the inverter was turned off. Once plugged into shore power, the inverter could be turned back on. Sometimes we would bypass the inverter when on GFIC shore power to isolate the inverter and potential trips.

This way we avoided the negatives to an IT such as space, noise, heat and cost.

 

[marcs]

2) Because you are using isolation transformers, you can simply tie all the neutrals together on the boat, and bond to ground at a single central point, typically at the load panel. This can often be a lot easier than trying to ensure only one bonding point is active at any given time.

All of twistedtree's advice aligns with my understanding and is very good, keeping in mind I'm an amateur and have only installed an isolation transformer once and very carefully studied E-11 at the time to do so.

I second the suggestion that a central bonding point probably makes this a lot easier to implement and understand both now and for any future modifications, but that won't work if your inverter can't disable its bonding. I don't think it can.

The other thing about your inverter is that it supports separate inputs for charger and transfer/passthrough. You don't have to use them.

NOTE: Freedom 25 Only. There are two options for configuring the AC input to the Freedom 25.
Dual Inputs: You may feed the internal battery charger separately from the transfer input which feeds the AC loads. In this case, connect one 30 Amp feed to the charger pigtails and another 30 Amp feed to the transfer switch input.
The advantage is to balance the AC loads when 2 legs of incoming AC power are available. These two feeds can be in or out of phase. Transfer will only occur when power is applied to both inputs. The charger can draw up to 27 Amps on one leg of power and the transfer switch can pass up to 30 Amps from the other leg of power.
Single Input: Feed both the battery charger and the transfer switch from the same AC input. In this case you will connect both pigtails together, Black to Black, White to White and Green to Green.

Side note. In reading E-11, it speaks on grounding on the metal case of the iso transformer. Because mine has a plastic housing, I wouldn’t need to ground there and my bonding would only be a jumper wire from my main ground bus to my main neutral bus?

Short answer, yes but only if using option 2. Option 1 requires tying them at the transformer so that the neutral is disconnected when that input isn't active, thus severing the connection. Ground is still connected but neutral isn't.

Other answer: Your isolation transformers (which brand/model are they?) can never comply with the current E-11 to the letter so that makes understanding things slightly more complex. A lot of parts of electrical safety aren't purely black and white and change as technology and understanding progresses.

This is where what twistedtree said about the content of the draft E-11 applies, which is what would cover your situation if approved and what brings in the RCD, so you won't be able to exactly mirror the published E-11. So you can no longer blindly follow advice in Steve's article or others.

To state that in different words, I'd probably be fine using your isolation transformers but would absolutely put a RCD before them. I haven't researched that scenario in depth though.

There is long running debate / accusations around just what is and isn't safe for isolation transformers and if standards are rigged to support certain manufacturer's products.

Peter:
We did this on our vessel even with no isolation transformer. Doing this cured our trips on the newer GFIC shore pedestals.

That seems odd and wrong at first glance if I'm understanding, without an isolation transformer the "source" of power electrically speaking is not on the boat and thus neutral and ground shouldn't be connected when on shore power. They are only connected when using a "source" that is on the boat, such as an inverter or generator. This is one of the reasons why two pole breakers / transfer switches are necessary.

Marcs:
Did you consider one 50 amp/240V vs the two 30 amp /110V shore power inlets?

I'm not the original poster, so not sure this is directed at me but ...

I absolutely would pick one 50 amp 240v over two 30 amp 110v any day for my uses. Gives you almost twice the total power and much more robust physical plugs and safety margins. But it really depends on what shore power connections are available where you boat. But that brings a whole other set of considerations into play and is a more involved project.

So if neutral and ground never get connected, why is it the Gen and Inverter connect them when running? What’s the difference? All 3 are AC power sources

The power source for shore power, without isolation transformers, is considered to be shoreside. That is where the neutral ground connection is made.


With an isolation transformer, the transformer is now the "source" of the power.

Corrections welcome if I've misstated anything in my attempts to clarify.

 

[SteveK]

For SeaBoy, something for your consideration....


When your shore connections run through isolation transformers, as yours do, ABYC allows for tying all the neutrals together, and bonding them to ground in one central location. I think I mentioned this in an earlier note too. This is my own preferred approach, and I think is much easier to implement, and much less prone to error vs bonding at each power source and ensuring that those bonds are always mutually exclusive regardless of what's powering what.

what you say makes sense if the ground on boat is not connected to the shore ground when an isolation transformer is used. The source of power is now the isolation transformer.

Residual Current Device (RCD). This needs more specific explanation. As I understand these when installed in dock pedastals are tripping if the boat has a leak. Is there a reason to get one on the boat before or after the Galvanic isolator?

 

[SeaBoy]

So because i cant disconnect the bond at the inverter when its running, that leaves me with option 1: creating separate neutral buses for Shore 1, Shore 2, and the inverter. Which brings me back to my original wiring schematic with the update to adding in breakers before the isolation transformers. my generator will run both shore 1 and shore 2 hot and neutral busses.

as for "grounding at the source" aka at my isolation transformers, can i just splice in a ground wire to the secondary side neutral out? in other words, crimp in a "Y" - iso Neutral crimped to ground wire. Note that i have a plastic casing and my iso does not comply with ABYC metal shielding/casing requirements

 

[SeaBoy]

Heres the link to the company i bought my isolation transformers from

https://www.bridgeportmagnetics.com/bmg-product/marine-puck-isolation-transformer-6000va/

 

[marcs]

So because i cant disconnect the bond at the inverter when its running, that leaves me with option 1: creating separate neutral buses for Shore 1, Shore 2, and the inverter. Which brings me back to my original wiring schematic with the update to adding in breakers before the isolation transformers. my generator will run both shore 1 and shore 2 hot and neutral busses.

as for "grounding at the source" aka at my isolation transformers, can i just splice in a ground wire to the secondary side neutral out? in other words, crimp in a "Y" - iso Neutral crimped to ground wire. Note that i have a plastic casing and my iso does not comply with ABYC metal shielding/casing requirements

I'm assuming the below diagram from Bridgeport Magnetic's site matches your transformer.

I would put ring terminals on the white and yellow and connect them to an enclosed bus bar, and also connect ground and your neutral feed continuing into the boat to that bus bar.

I'd take a separate bus bar (could just be a "terminal stud") and put ring terminals on black and red, then connect that to your hot feed continuing into the boat.

All AC connections should be enclosed to prevent accidental contact.

I don't like Y splices, especially for higher power circuits. Not sure if ABYC approves or not.

I'm not sure if your diagram includes all the things required to make this correct or not, I haven't studied it in detail or reviewed all of twistedtree's comments in detail.

 

[SeaBoy]

I'm assuming the below diagram from Bridgeport Magnetic's site matches your transformer.

I would put ring terminals on the white and yellow and connect them to an enclosed bus bar, and also connect ground and your neutral feed continuing into the boat to that bus bar.

I'd take a separate bus bar (could just be a "terminal stud") and put ring terminals on black and red, then connect that to your hot feed continuing into the boat.

All AC connections should be enclosed to prevent accidental contact.

I don't like Y splices, especially for higher power circuits. Not sure if ABYC approves or not.

I'm not sure if your diagram includes all the things required to make this correct or not, I haven't studied it in detail or reviewed all of twistedtree's comments in detail.

Perfect! makes sense. i can make this work. ill send an update to my electrical schematic to see what you guys think for some final comments

 

[twistedtree]

All of twistedtree's advice aligns with my understanding and is very good, keeping in mind I'm an amateur and have only installed an isolation transformer once and very carefully studied E-11 at the time to do so.

I second the suggestion that a central bonding point probably makes this a lot easier to implement and understand both now and for any future modifications, but that won't work if your inverter can't disable its bonding. I don't think it can.

The other thing about your inverter is that it supports separate inputs for charger and transfer/passthrough. You don't have to use them.




Short answer, yes but only if using option 2. Option 1 requires tying them at the transformer so that the neutral is disconnected when that input isn't active, thus severing the connection. Ground is still connected but neutral isn't.

Other answer: Your isolation transformers (which brand/model are they?) can never comply with the current E-11 to the letter so that makes understanding things slightly more complex. A lot of parts of electrical safety aren't purely black and white and change as technology and understanding progresses.

This is where what twistedtree said about the content of the draft E-11 applies, which is what would cover your situation if approved and what brings in the RCD, so you won't be able to exactly mirror the published E-11. So you can no longer blindly follow advice in Steve's article or others.

To state that in different words, I'd probably be fine using your isolation transformers but would absolutely put a RCD before them. I haven't researched that scenario in depth though.

There is long running debate / accusations around just what is and isn't safe for isolation transformers and if standards are rigged to support certain manufacturer's products.



That seems odd and wrong at first glance if I'm understanding, without an isolation transformer the "source" of power electrically speaking is not on the boat and thus neutral and ground shouldn't be connected when on shore power. They are only connected when using a "source" that is on the boat, such as an inverter or generator. This is one of the reasons why two pole breakers / transfer switches are necessary.



I'm not the original poster, so not sure this is directed at me but ...

I absolutely would pick one 50 amp 240v over two 30 amp 110v any day for my uses. Gives you almost twice the total power and much more robust physical plugs and safety margins. But it really depends on what shore power connections are available where you boat. But that brings a whole other set of considerations into play and is a more involved project.





The power source for shore power, without isolation transformers, is considered to be shoreside. That is where the neutral ground connection is made.


With an isolation transformer, the transformer is now the "source" of the power.

Corrections welcome if I've misstated anything in my attempts to clarify.

That all sounds right.


I will comment on this notion that keeps coming up that ABYC is loaded with vendors with their hands on the scale, and it's really not true, or at least not in any area that I have been involved with over the past 4 years.

 

[twistedtree]

what you say makes sense if the ground on boat is not connected to the shore ground when an isolation transformer is used. The source of power is now the isolation transformer.

Residual Current Device (RCD). This needs more specific explanation. As I understand these when installed in dock pedastals are tripping if the boat has a leak. Is there a reason to get one on the boat before or after the Galvanic isolator?

When you use an isolation transformer, the shore ground and boat ground are not connected, as you suspected.


RCDs are finding their way into more and more placed on boats. Most people are familiar with their appearance in the shore power infrastructure, and that is surfacing lots and lots of wiring errors on boats. It's a pain when it's your boat, but doing everyone a service in the long run.


RCDs are also now required under certain circumstances on the boat itself. I don't know them all off hand, but they are increasingly being used as the first breaker onboard after the shore power inlet.

 

[twistedtree]

So because i cant disconnect the bond at the inverter when its running, that leaves me with option 1: creating separate neutral buses for Shore 1, Shore 2, and the inverter. Which brings me back to my original wiring schematic with the update to adding in breakers before the isolation transformers. my generator will run both shore 1 and shore 2 hot and neutral busses.

as for "grounding at the source" aka at my isolation transformers, can i just splice in a ground wire to the secondary side neutral out? in other words, crimp in a "Y" - iso Neutral crimped to ground wire. Note that i have a plastic casing and my iso does not comply with ABYC metal shielding/casing requirements

Yes, that's how I would do it if pursuing a distributed n-g bonding strategy.

 

[marcs]

That all sounds right.
I will comment on this notion that keeps coming up that ABYC is loaded with vendors with their hands on the scale, and it's really not true, or at least not in any area that I have been involved with over the past 4 years.

Indeed, I don't mean to suggest it is loaded and thank you for clarifying. I just mean that on this specific issue of isolation transformers and grounding shields it has been suggested by some folks involved with the process that it is in existing manufacturers best interest to not allow other options. This was well over 4 years ago I was researching that though. It is always tricky to piece apart from afar because such manufacturers are often also subject matter experts and writing standards is hard.

I have no personal first hand knowledge.

 

[SeaBoy]

When you use an isolation transformer, the shore ground and boat ground are not connected, as you suspected.


RCDs are finding their way into more and more placed on boats. Most people are familiar with their appearance in the shore power infrastructure, and that is surfacing lots and lots of wiring errors on boats. It's a pain when it's your boat, but doing everyone a service in the long run.


RCDs are also now required under certain circumstances on the boat itself. I don't know them all off hand, but they are increasingly being used as the first breaker onboard after the shore power inlet.

Twisted Tree - in my scenario with isolation transformers, if my dock power has shore RCDs, wouldnt an RCD before my transformer basically be useless? In the interest of money I’m thinking about a standard double pole breaker before the iso, and an RCD after to supply the panel

 

[Bmarler]

Twisted Tree - in my scenario with isolation transformers, if my dock power has shore RCDs, wouldnt an RCD before my transformer basically be useless? In the interest of money I’m thinking about a standard double pole breaker before the iso, and an RCD after to supply the panel

rcd at the boat inlet is best in your case.
not all dock power you come across will have one.

 

[twistedtree]

With the Bridgeport device, I think this is how it needs to be hooked up. With a distributed n-g bonding arrangement, it absolutely needs to be double pole because so when you disconnect the power source, you also disconnect the bonded neutral. And I'm pretty sure it's also required regardless of the bonding strategy, but a more careful read of E-11 would be needed to be sure.

 

[marcs]

Twisted Tree - in my scenario with isolation transformers, if my dock power has shore RCDs, wouldnt an RCD before my transformer basically be useless? In the interest of money I’m thinking about a standard double pole breaker before the iso, and an RCD after to supply the panel

My two cents, for what they are worth...

Your boat won't always be at your home dock and you aren't in charge of maintenance on the shore side. Unless it is literally your own dock, of course, and you never plug in anywhere else and this is your boat until you die.

It is key from a standards and safety perspective to not assume more than necessary about the shore side. Only you can judge that balance.

I'm also not sure offhand what the specs are for RCDs as far as trip current or response time on the shore power side versus the boat side, they may differ for good reason. Other than a difference in trip current or response time, electrically speaking I'm not coming up with a reason that RCDs on the shore side wouldn't provide RCD protection in case of isolation transformer faults. Again, not a professional.

I definitely understand the cost issues and wanting to figure out where to draw the line.

 

[twistedtree]

Twisted Tree - in my scenario with isolation transformers, if my dock power has shore RCDs, wouldnt an RCD before my transformer basically be useless? In the interest of money I’m thinking about a standard double pole breaker before the iso, and an RCD after to supply the panel

I'm not an RCD expert, but I think you are correct that an RCD both on shore and on the boat would be redundant. However there is no certainly that the shore side will have an RCD. And in the case of a toroidal transformer like the Bridgeport, it was viewed as a way to recover some of the protection afforded by an internal ground shield in a conventional transformer. That's why it's always required with a toroidal transformer.

 

[marcs]

With the Bridgeport device, I think this is how it needs to be hooked up. With a distributed n-g bonding arrangement, it absolutely needs to be double pole because so when you disconnect the power source, you also disconnect the bonded neutral. And I'm pretty sure it's also required regardless of the bonding strategy, but a more careful read of E-11 would be needed to be sure.

Ah yes, I missed that. My understanding about requiring a double pole breaker agrees with yours.


There may be some exceptions in E-11 for simpler systems based on the idea you can't have reverse polarity out of an isolation transformer (unlike a bad shore power hookup), but I don't think they would apply here if so.

 

[Bmarler]

I'm not an RCD expert, but I think you are correct that an RCD both on shore and on the boat would be redundant. However there is no certainly that the shore side will have an RCD. And in the case of a toroidal transformer like the Bridgeport, it was viewed as a way to recover some of the protection afforded by an internal ground shield in a conventional transformer. That's why it's always required with a toroidal transformer.

that was my take on it as well. the 10 foot exception doesn't apply here.

 

[SeaBoy]

With the Bridgeport device, I think this is how it needs to be hooked up. With a distributed n-g bonding arrangement, it absolutely needs to be double pole because so when you disconnect the power source, you also disconnect the bonded neutral. And I'm pretty sure it's also required regardless of the bonding strategy, but a more careful read of E-11 would be needed to be sure.

See new sketch. It’s simplified but I think we all get the point. Forgot to draw the Gen ground

 

[jhall767]

Marcs:
Did you consider one 50 amp/240V vs the two 30 amp /110V shore power inlets?

The downside of this is that a 240V isolation transformer won't like being connected to a 120V single 30 amp if that is all that is available. At least according to the engineers of my transformer.

 

[SteveK]

So because i cant disconnect the bond at the inverter when its running, that leaves me with option 1: creating separate neutral buses for Shore 1, Shore 2, and the inverter. Which brings me back to my original wiring schematic with the update to adding in breakers before the isolation transformers. my generator will run both shore 1 and shore 2 hot and neutral busses.

as for "grounding at the source" aka at my isolation transformers, can i just splice in a ground wire to the secondary side neutral out? in other words, crimp in a "Y" - iso Neutral crimped to ground wire. Note that i have a plastic casing and my iso does not comply with ABYC metal shielding/casing requirements

In my understanding loads that are fed by or through the inverter use the inverter auto switch for bonding neutral/ground when inverting and not bonding when AC is pass thru.

If I need more than the 30amp shore power provides I turn off the feed to the inverter and let it supply the inverter loads separate from shore loads.

 

[twistedtree]

See new sketch. It’s simplified but I think we all get the point. Forgot to draw the Gen ground

That's looking good. I would probably still replace the inverter and build with a single neutral bus with central grounding. I suspect it's just a matter of time before you will want/need a sine wave inverter anyway, and I think a single neutral bus will be much easier to keep track of and keep sorted correctly in the future vs three separate neutral busses. You might even find that the existing inverter trips the RCDs on the boat. It's hard to predict, but not uncommon to encounter older inverters where the bonding relay switches slower than the RCD response time, and trips the RCD everytime it switches back and forth between shore power and inverter-only. It might be worth bench testing it before getting too far down one path.

 

[Bmarler]

See new sketch. It’s simplified but I think we all get the point. Forgot to draw the Gen ground

i like it, but where are you inserting the inverter?

 

[tiltrider1]

The downside of this is that a 240V isolation transformer won't like being connected to a 120V single 30 amp if that is all that is available. At least according to the engineers of my transformer.

My boat is all 120v except a dryer. Here I use a step up transformer. This allows the boat to function when only 120v is available. I have been considering the Bridgeport IT because it can be wired in such a way as to be functional when only 120v 30a is available and when 250/125v 50a is available.

Last time I checked ABYC required ground shield connection and since this is not possible with a Bridgeport IT it wasn’t ABYC approved although they mentioned they would be looking into a rewrite to include toroidal IT.

 

[SeaBoy]

i like it, but where are you inserting the inverter?

Thinking about coming from Shore 1 main breaker. It’ll go from there, to the inverter, then to a sub panel, with circuit protection. Here’s a snip from the inverter manual:

 

[Bmarler]

Thinking about coming from Shore 1 main breaker. It’ll go from there, to the inverter, then to a sub panel, with circuit protection. Here’s a snip from the inverter manual:

I see. If everything on shore 1 is going to be inverter loads this might be of interest.
I had a xantrex freedom 2000 watt inverter/charger with a 30 amp pass through relay. When I loaded the pass through heavily, it would drop out. I think the 30 amp rating was not continuous, and I didn’t realize the inverter would disconnect the loads when on shore power.
I ended up upsizing the inverter to one with a 50 amp pass through, problem solved. I can fully load my 30 amp panel as designed.

 

[SeaBoy]

Not everything on shore 1 will be inverter loads. Shore 1 will cover:
-water heater
-12v battery charger
-24v battery charger

Inverter will piggy back to a sub panel which will feed:
-Outlets
-galley outlets
-refrigerator

Shore 2 will cover:
-mid cabin air conditioner
-aft cabin air conditioner
-raw water pump for air conditioners

 

[Bmarler]

Not everything on shore 1 will be inverter loads. Shore 1 will cover:
-water heater
-12v battery charger
-24v battery charger

Inverter will piggy back to a sub panel which will feed:
-Outlets
-galley outlets
-refrigerator

Shore 2 will cover:
-mid cabin air conditioner
-aft cabin air conditioner
-raw water pump for air conditioners

Sounds good. On my last boat I had a split panel for inverter/ non inverter loads. I was able to split the busses behind the breakers for the respective loads, and didn’t have to put in a separate remote panel.

 

[PierreR]

This thread is of great help for me to even get started on figuring out what I have installed on my boat.