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!

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4 thoughts on “Isolating AC power”

  1. 8/9/20
    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

    • Hi Charlie,

      I probably should not have posted the picture of the Battle Born batteries – that was an interim picture before the final two of 8 batteries were put in place, with some temporary connections both on the batteries and the jumpers.

      Just to address some of your points:

      1. Battle Born bank
      > The batteries are secured both side to side, top to bottom, and do not move hardly at all, let alone the 1 inch required (which seems like too much to me!)
      > All terminals, busses, and ends have insulating covers / heat wrap
      > This was definitely temporary just to have some house power while finishing the install. The takeoffs are at opposite ends of the bank.

      2. Interesting feedback on the Bridgeport. I was under the impression they were fully ABYC compliant, and this is very concerning. I am going to see if they can clarify their stance, as some of the verbiage on their website appears to have changed since I purchased the device….

      Victron’s isolation transformer is great, but it is also much larger, which was a problem with my setup. If Bridgeport can’t provide proper details in their response, though, I will likely be changing to theirs since I already have a lot of Victron equipment on board, and have used and loved them.

  2. Steve,

    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.

    • Hi Jim,

      Thank you for posting this. I wouldn’t say this is arcane and technical – this is why I post things – to share information with people about technologies and projects. If it is installed incorrectly, or the information I have is not right, I want to know. Not only do I not want my readers to follow it, but I personally do not want something wrong on my boat in any way, shape or form.

      What is very disappointing to me in general is that I had an ABYC-certified electrician review product prior to purchasing it, as well as be part of the installation. At no point were some of the things you brought up discussed. I will handle that conversation on my own, as I expected that by consulting someone versed in the standards more than me, and who does this for a living would have caught at least one or more of these items.

      I’m familiar with the difference between isolation and polarization transformers. I will admit my notes about galvanic isolation and AC isolation/protection are confusing. I guess I can’t be right all the time 🙂 The intent was to talk about the galvanic corrosion issues and whether a transformer or galvanic isolator were better/worse.

      I asked multiple times of Bridgeport as well as my electrician how capping the shore ground and not having anything beyond that was safe. The answer provided revolved around how the puck worked, etc. I should have persisted, as having worked on electrical systems for years, this made no sense to me.

      To make sure I understand:

      This product could likely only be used in the polarization configuration, and only if it were to have some sort of case ground. It would also need a galvanic isolator (which I already have). However, the product isn’t in a case, and provides no way to ground it that I’ve seen. They sell a version that has a “boost” add-on which is in a case, but I am not aware as to whether it includes some sort of ground.

      Beyond that, it does not comply with UL1561. If it were being used in the polarization configuration I assume ABYC E11 wouldn’t be applicable.

      I’m pretty disappointed in general with how this has turned out. It didn’t feel right throughout the process before purchase, and now it feels even worse.

      I went back after Charlie posted and re-read David Rifkin’s article from a long while ago on “Isolation or Polarization: Which is the Safest Transformer Installation?” and started doubting that this product is (a) really ready for boats in any way and (b) was correctly installed.


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