Isolating AC power

You may notice that this article is quite short. After a few comments (scroll down) and a number of email discussions on the side, I decided to remove the content of this article and replace it with this info.
Steve Mitchell 5 min read
Isolating AC power

Hi there,

You may notice that this article is quite short.  After a few comments (scroll down) and a number of email discussions on the side, I decided to remove the content of this article and replace it with this info.

There are serious concerns over the way this product was installed, and whether it is fully ABYC compliant.

It is clear to me that the installation represents a credible shock hazard  – the exact opposite of what I was trying to achieve.

At this time, it does not look like this product is ABYC Standard E-11 compliant in how it is grounded and also in terms of UL 1561.

I pride myself in documenting projects with technically backed, facts based research. I consulted with an ABYC electrician prior to purchasing, and during the install of this product. I also contacted the manufacturer and asked questions about the product. At no point was it outlined that this product does not fully conform to all necessary ABYC standards.

As such, I do not recommend the product at this time, and have removed it from use on my boat.

If I get updated information from the manufacturer, I will be sure to post it here. Otherwise, I would suggest looking at traditional isolation transformers from Victron and other manufacturers.

Thanks for your patience!

Archived Comments

These are read only comments from the old system. Scroll down to participate in SeaBits Discussions, our new interactive forum attached to each article.

Charlie Johnson
August 9, 2020 at 7:13 pm
I enjoy your articles and the meticulous manner in which you do your modifications.
In your latest posting I saw some issues.
1. Your Battle Born battery bank is well executed with the following exceptions:
> The batteries are not secured IAW ABYC Standard E-10
> There are several B+ terminals and busses that have no insulating boot or cover on them.
> Both the B+ and the B- takeoffs from the battery bank are from one end of the paralleled batteries. The batteries furthest away from these connections will be under utilized under load and take longer to charge. Correction is easy: take the B+ from the fuse block end of the bank and the B- from the far end.
2. The puck isolation transformer is not compliant with ABYC Standard E-11.
> There is no apparent electrostatic shield between the primary and the secondary windings.
> A “standard” isolation transformer is required to have a safety ground connection between the electrostatic shield and shore safety ground. Since there is no shield, there is no redundant path back to the shore source.
> The N and G are required to be bonded together at the secondary of the isolation transformer (and all sources of power on board). This bond is not shown on the drawing.
I have been waiting for Bridgeport Magnetics to develop a compliant transformer. As an aside, the Victron Isolation Transformer uses a toroidal transformer with a proper shield and N > G bonding on the secondary.
Charlie Johnson
ABYC Master Technician

Jim Healy
August 9, 2020 at 9:04 pm
I apologize in advance for sounding critical. I like your articles and your work. I do have concerns with this particular piece.
I had the same observations that Charlie Johnson reported, so I won’t repeat. I will tag on what Charlie said to add, this particular transformer might be usable on a boat – and also be in compliance with ABYC E11 – 1) IF IT IS WIRED AS A POLARIZAtION TRANSFORMER AND HAS A PROPER GROUND PATH BACK TO SHORE, and 2) if it is tested and in compliance with UL1561. A Polarization Transformer configuration DOES NOT require the shield between primary and secondary, and does not require a metallic external case. The polarization transformer configuration would require a galvanic isolator for blocking DC galvanic voltages.
You begin this post by saying “The two most common ways of isolating your AC power are a galvanic isolator or an isolation transformer.” I found this a little confusing, because it’s not clear that what you are “isolating” is small DC voltages. Where galvanic isolators are used, they are used to block very small DC voltages, thereby blocking very small, damaging DC currents. Galvanic isolators DO NOT block transient AC fault currents in the AC safety ground. Isolation transformers (more properly called “shore power transformers” because they can be wired in ISOLATION or POLARIZATION configurations) happen to isolate DC currents, but they also cut the AC ground path back to shore. That creates two new potential issues when there is an AC fault. First, in the case of an ABYC-compliant ISOLATION transformer, a short between the shield and the secondary side of the transformer creates a path for current in the water, leading to the discussion of the relative safety impacts in salt vs fresh water. And second, the input side of the PUCK, with a “capped off” ground as you described in the article, leaves the shore power connection to the boat (the primary side of the transformer) without a safety ground of any kind, which is a clear violation of ABYC E11, and a not insignificant fire and shock risk.
The ABYC Electrical Standard, E11, calls out compliance to UL 1561, “Dry Type General Purpose and Power Transformers,” for all shore power transformers (isolation and polarization) and then calls out ( several additional requirements for transformers used in the “isolation” configuration. This PUCK unit does not appear to comply in either case.
In general, the most safe shore power transformer configuration is the polarization configuration, with galvanic isolator, precisely because there is a continuous AC safety ground to shore. But, ABYC does permit the isolation configuration. Please alert your readers to these concerns, which I know are arcane and technical.

craig sauer
May 19, 2021 at 1:00 pm
So what is the latest? Does Bridgeport or any other manufacturer produce something like this that can be compliant and work so as not to trip the pedestal breaker?
I would like to purchase one of these as soon as possible. Thanks

  • Steve Mitchell
    May 19, 2021 at 1:42 pm
    Nothing has changed since I wrote this post. There were some emails back and forth between me, the manufacturer, and various regulatory agencies, but it still does not conform to ABYC, so I won’t be using it aboard my boat. There’s a bigger discussion about the type of device it is versus a traditional isolation transformer, and which one is better, as well as the spec itself, but as it stands, I don’t feel comfortable using this aboard my boat until the basic compliance issue is addressed.
    It sucks since it is such a quiet and compact device….

E Smith
September 16, 2021 at 2:42 pm
From the Bridgeport Magnetics website:
“Our Marine-Puck family recently acquired UL Marine certification for the US and Canada. (E509703)”
“Marine-Puck complies with ABYC Standard E11.17.3.5, Polarization Transformers, except for the enclosure being non-metallic.”

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