Isolation Transformer Neutral Ground Connections

[SeaBoy]

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.

That’s how mine is set up now. However I already have a sub panel that currently is not in use. I like the identification of knowing what is/isnt inverter loads for future owners. And it’s impossible to back feed the inverter too (well, almost impossible)

 

[Bmarler]

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

There are some very talented people here to shed light on things like this. Many of us are skilled with electrical in general, but if you want to be abyc compliant, some of the little nuances of e-11 can be difficult to sort out. Folks here with that knowledge are willing to share, and it’s a great resource.
If I remember correctly, you and I are in about the same place in rotator recovery. Going well for you? I getting back to being able to do things again, been a long haul.

 

[marcs]

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:

Without an isolation transformer, you need to separate the neutral bus for circuits on the inverter or you risk tripping shore side ELCIs. (This thread may come full circle...) https://www.pysystems.ca/resources/articles/elci-breaker-with-an-inverter-charger/

It intuitively feels like this may not be needed if you are behind isolation transformers (and in fact is one reason people install them) but just because it feels that way doesn't make it true as there can be multiple reasons for doing something. I have less experience in that aspect.

I also want to call out that you shouldn't trust the inverter manual too closely as it was never written with ABYC compliance in mind and things have changed since then.

 

[SeaBoy]

Without an isolation transformer, you need to separate the neutral bus for circuits on the inverter or you risk tripping shore side ELCIs. (This thread may come full circle...) https://www.pysystems.ca/resources/articles/elci-breaker-with-an-inverter-charger/

It intuitively feels like this may not be needed if you are behind isolation transformers (and in fact is one reason people install them) but just because it feels that way doesn't make it true as there can be multiple reasons for doing something. I have less experience in that aspect.

I also want to call out that you shouldn't trust the inverter manual too closely as it was never written with ABYC compliance in mind and things have changed since then.

I’ll give it a read.

And yes. All AC power sources will have individual neutrals. Except when the Gen is online. It will share shore 1 and shore 2 neutral busses

 

[marcs]

I’ll give it a read.

And yes. All AC power sources will have individual neutrals. Except when the Gen is online. It will share shore 1 and shore 2 neutral busses

Just to be clear, I'm suggesting you may need separate neutral busses for the loads powered off the inverter, unless that is not required with an isolation transformer.

Many installs don't do this because it requires tracing down the neturals for each circuit on the inverter.

Apologies if you already do understand this.

 

[Trawlerman]

Without getting into the grounding issue on the output side of transformers, the first thing that caught my eye in your schematic is that you have the outputs of the two transformers directly paralleled, but since you are running these from two 30 amp shore-power cords, and normally, these are are 180 out of phase relative to each other, things could get very exciting when you plug them in, depending on how the wave-forms at the two secondaries are (either in same phase relationship or anti-phase relative to each other). . In addition, and perhaps of even more importance, your schematic is liable to get somebody killed. For example, the secondary winding of transformer #1 is connected directly to the secondary of transformer #2. Bearing in mind that one-to-one transformers "work" equally well in either direction, this means that the minute you put power on to the primary of transformer #1, it will energize the secondary of transformer #2, and that will in turn energize the primary of transformer #2 and electrocute the guy working on the shorepower leg that he thought he had killed at the breaker. Here you could very well be making "hot" the "shore 2" in your diagram. Strongly suggest you get some help on the project.

 

[SeaBoy]

Without getting into the grounding issue on the output side of transformers, the first thing that caught my eye in your schematic is that you have the outputs of the two transformers directly paralleled, but since you are running these from two 30 amp shore-power cords, and normally, these are are 180 out of phase relative to each other, things could get very exciting when you plug them in, depending on how the wave-forms at the two secondaries are (either in same phase relationship or anti-phase relative to each other). . In addition, and perhaps of even more importance, your schematic is liable to get somebody killed. For example, the secondary winding of transformer #1 is connected directly to the secondary of transformer #2. Bearing in mind that one-to-one transformers "work" equally well in either direction, this means that the minute you put power on to the primary of transformer #1, it will energize the secondary of transformer #2, and that will in turn energize the primary of transformer #2 and electrocute the guy working on the shorepower leg that he thought he had killed at the breaker. Here you could very well be making "hot" the "shore 2" in your diagram. Strongly suggest you get some help on the project.

Trawlerman - can you please point out on my schematic how I have the transformers in parallel?? I fail to see what you’ve identified

 

[Helmsman]

Seaboy, I am not an electrician, but I have studied these transformers and have two Victron IT’s on my boat. I would be wary of having the shore side ground unattached in case of a failure of the transformer itself. The concern is that the transformer fails through an inherent defect, lightning, extended overloads, etc. There is a reason the ground wire is attached to the shield. The SP breaker would then disconnect if there is a ground fault. Unlikely? Yes. Consequential? Certainly could be.

When I looked at the Bridgestone Toroidal a year and a half ago, the lack of the ground connection, and if I remember correctly the wires were not potted, which could result in problems. I also remember some discussion that Bridgestone was planning to address those concerns. I am not sure whether they have.

I hesitated to post this because I lack the expertise to. If there is an ABYC electrician on the forum, perhaps they could weigh in on the above concerns.

 

[SeaBoy]

I would like l to hear your thoughts about your comment on me “killing someone” with my current wiring set up. That was a pretty bold statement to say and then not address on a public message

Also, if I get a short in the unit, the casing is insulated and plastic, and with the primary side or secondary side RCD breakers would pick it up. And I don’t even know how wires wrapped around a core would short but stranger things have happened

 

[twistedtree]

Trawlerman - can you please point out on my schematic how I have the transformers in parallel?? I fail to see what you’ve identified

I think the part that Trawlerman is missing is that the pairs of breakers are interlocked so only one can be on at a time. This was in your earlier drawing and discussed, but is not show in the latest drawing.

 

[Helmsman]

Seaboy, You may have already seen this in regards to the Bridgestone products. Please take a look at the comments section of the SeaBits article. Both Charlie and Jim are long time advisors on electrical issues. Charlie is active on Cruiser Forum. Jim works with ABYC on E-11. He is extremely knowledgeable and his website has excellent information on all things marine electric. He is a member of both the AGLCA and MTOA and has helped me with several electrical concerns.

https://seabits.com/isolating-ac-power/

Jims website

https://gilwellbear.wordpress.com/category/boat-technical-topics/electrical-topics/

 

[Helmsman]

Notice the wording in the second paragraph limits conformance (with the exception of no shield) to the ABYC standard to a polarized set up, as opposed to it being set up as an isolation transformer. It does state that the wiring is potted which was one of my two original concerns with the product.

From the Bridgeport site:

“Marine-Puck feature toroidal (ring shaped) isolation transformers which are much lighter and more compact than traditional transformers. When turned on they may experience a brief Inrush Current surge, which may in a rare event cause the input circuit breaker to trip. In our experience an efficient remedy is selecting a D-curve (delayed action) circuit breaker. – Another solution is to mitigate the Inrush surge by pre-magnetizing the core briefly as the transformer is turned on. A convenient way to do this is to install resistors in the form of quartz halogen bulbs across the contacts in the input circuit breaker. The circuit breaker is opened before the shore cable is plugged in causing a low current to pass before the transformer is fully turned on by closing the input breaker. The bulbs are only on at reduced power during the time between plug in and turn on and will never need to be replaced.

Marine-Puck complies with ABYC Standard E11.17.3.5, Polarization Transformers, except for the enclosure being non-metallic. A grounded metallic enclosure would run counter to the general trend towards composite or plastic junction boxes, and ne-gate Marine-Puck’s status as a class II device. The Marine-Puck ABS enclosure combined with the solid epoxy potting com-pound eliminates shock and fire hazards due to broken or loose conductors touching a metallic case besides effectively pre-venting sea water from entering the transformer.“

 

[twistedtree]

Seaboy, You may have already seen this in regards to the Bridgestone products. Please take a look at the comments section of the SeaBits article. Both Charlie and Jim are long time advisors on electrical issues. Charlie is active on Cruiser Forum. Jim works with ABYC on E-11. He is extremely knowledgeable and his website has excellent information on all things marine electric. He is a member of both the AGLCA and MTOA and has helped me with several electrical concerns.

https://seabits.com/isolating-ac-power/

Jims website

https://gilwellbear.wordpress.com/category/boat-technical-topics/electrical-topics/

I've been looking at all this today as part of the revision work on E-11, and both Charlie's and Jim's comments touch on something that I also came across today, which is that the Bridgeport device doesn't meet UL1561, and that is required for compliance even with the proposed language to accept toroidal transformers in general. So even with the revisions that are currently on the table, the Bridgeport device still wouldn't comply.

 

[Helmsman]

Seaboy,
When I looked at the Bridgestone Toroidal

Bridgeport, not Bridgestone!