Galvanic Isolator or Isolation Transformer

[s/v Jedi]

Originally Posted by Jammer

I think you will find that the problem was that you connected the ground from shore power to your Victron isolation transformer as though it were a USA-standard unit with a shield. Victron transformers have toroidal windings which do not allow a shield to be placed between the primary and secondary windings. USA/ABYC wiring practices require a shield, and the shore power ground is brought to the shield (only!) which has its own special clearly-marked ground terminal in the transformer enclosure.

European wiring practices don't require the shield. Use of the shield significantly increases the size, weight, and cost of the transformer. In European practice it is believed that a residual current breaker provides sufficient protection so the shield isn't necessary.


Had the isolation transformer been wired correctly, the shore power ground would not have been connected to anything, and so there would have been no place to connect the galvanic isolator.

I don’t see how such a wiring error is possible when following instructions. There is a ground jumper though, which may have been left connected and voids protection. The jumper is only to comply with code while hauled out and using shore power while on the hard.

[sailcrazy]

We did wire per the instructions, and then had our wiring verified by Victron a couple of telecons. And no, we did not put the ground jumper in. Basically, we ran the 3 conductors from the shore power inlet to the transformer input (live, neutral, and ground), and then the 3 conductors from the xfmr output to the dist panel. When I installed the galvanic isolator, I broke the ground conductor from the shore power inlet to the xfmr, and installed the isolator on that line. I replaced all the conductors with new, in the off chance there was a break or holiday in the insulation of one of the conductors, inside the wire bundle, that might be allowing a current path I didn't intend.

[s/v Jedi]

Originally Posted by sailcrazy

We did wire per the instructions, and then had our wiring verified by Victron a couple of telecons. And no, we did not put the ground jumper in. Basically, we ran the 3 conductors from the shore power inlet to the transformer input (live, neutral, and ground), and then the 3 conductors from the xfmr output to the dist panel. When I installed the galvanic isolator, I broke the ground conductor from the shore power inlet to the xfmr, and installed the isolator on that line. I replaced all the conductors with new, in the off chance there was a break or holiday in the insulation of one of the conductors, inside the wire bundle, that might be allowing a current path I didn't intend.

Right, so the install was correct and I assume you verified no connection between shore ground and ships ground using the multimeter.

There could have been a stray current field from the boat in the next slip etc. but one thing is sure, it was not your shore power.

[Groathill]

Hi,
I intend to install a smaller isolation toroid transformer without a shield. As I am in Europe, I understand this is OK.


Question 1: Should I or should I not connect the earth wire (usually with yellow/green colours) from the marina outlet to the internal boat AC circuits past the transformer?



There are an RCD and several parallel automatic fuses for the boat's internal 230VAC system.



Question 2: Can I or should I not use an isolation breaker in combination with an isolation transformer - if yes does it make sense?


A simple circuit diagram would be very much appreciated.


Thanks!

[smac999]

connecting the boats ground to the dock compleaty ruins the whole point of having an isolation transformer. which is to stop the ground. on the output the transformer you should be be connecting the boat ground and neutral conductor (blue over there?) together. creating your own ground return loop on the boat. if the isolatrion transformer has no ground input. then I guess the dock ground goes nowhere. the case of the transformer itself is likly on the ground output. so you don't want to ground the dock to the case.

you should have a main double pole RCD breaker before the transformer. and probably a double pole main breaker after as well (probably already on panel)

[Bycrick]

If one uses an isolation transformer, the safety ground doesn’t need to be connected on the boat unless the transformer has a metal case or a shield between the two windings. Either/both of those are supposed to be connected to the safety ground wire ashore.

[smac999]

Originally Posted by Bycrick

If one uses an isolation transformer, the safety ground doesn’t need to be connected on the boat unless the transformer has a metal case or a shield between the two windings. Either/both of those are supposed to be connected to the safety ground wire ashore.

The victron metal case is internally attached to the output (boat side) ground. So you defiantly don’t want to ground the case to the dockside. Or you have just re injected the shore ground to the boat ground.

[Bycrick]

In all cases, one should read the manual. In most cases, it’s a good idea to follow the manual. The question was general, I thought: with an isolation transformer, should one carry the shoreside safety ground into the boat's electrical system. The general answer is "no."

However, if the transformer has a metal case, you don’t want to leave it "unconnected" because various failures could leave it electrically hot. The few isolation transformers I’ve seen over the years have the metal case connected to the safety ground, so that an internal failure will cause a fault to ground.

Some transformers have a shield between the two windings to insure that you can’t get a failure that inadvertently connects the input and output windings. That too is normally connected to the shoreside safety ground for the same reason as the case.

But I’m sure that Victron knows what they’re doing. The only possible gotcha is the differences between US and non-US codes for AC electrical wiring.

[s/v Jedi]

Victron has a ground terminal for shore ground and a ground terminal for boat ground. Then they have a ground jumper which connects the two: this is normally -not- installed. Code requires to install the jumper when shore power is used during a haul out.

This is how it must be done with a Victron isolation transformer. AFAIK, it conforms to code worldwide, for sure in the EU and the US.

[Bycrick]

The approach you described sounds right to me. The case and shield normally connected to shore-side safety ground and isolated from the boat. When you’re on the hard, you connect the shore-side safety ground to the boat-side safety ground with the jumper.

[s/v Jedi]

Originally Posted by Bycrick

The approach you described sounds right to me. The case and shield normally connected to shore-side safety ground and isolated from the boat. When you’re on the hard, you connect the shore-side safety ground to the boat-side safety ground with the jumper.

It is not “my approach”, it is how it’s done by every installer and owner who read the manual

[Bycrick]

Please don’t try to put words in my mouth. I didn’t talk about "your approach." The original post was simply whether or not the shoreside safety ground wire was connected on the boat when one had an isolation transformer. The answer, as often happens, isn’t binary, as shown by your description of the Victron wiring.

So, being very specific:
1. The green or green-yellow wire must be carried through from the shore power connection. Hopefully the dock wiring is properly done and takes that back to the main feeder.
2. The shoreside safety ground is internally connected to any internal transformer Inter-winding shield and to the case of the transformer if it’s conductive. This is the responsibility of the transformer manufacturer. The implication here is that you always need a 3-wire shore power cable since every approved isolation transformer I’ve seen has a metal case.
3. If the boat is in the water, the shoreside safety ground is NOT connected to anything on the boat except as in the previous item.
4. If the boat is NOT in the water, then you are supposed to connect the shore- and boat-side safety grounds together temporarily so that anything plugged into the boat circuits are properly grounded.

Is that better?

It seems Victron follows those rules.

[alaskanviking]

Good morning!

I did a lot of research developing an AC power system similar to S/V Jedi, which started with power coming into the boat to an isolation transformer.

To answer the original poster. A galvanic isolator minimizes but does not disconnect the ground coming from shore power. It prevents minor voltage flow to and from the boat to stop galvanic corrosion. You have zinc, bronze, and stainless on the bottom of your boat ie electrodes, in a salt water bath making a battery. The electrodes on your boat are connected to electrodes on other boats by the shore power ground cable, to make a big battery. worse If any stray ac current happens the current will go to whichever closest ground connection (really eating your zincs).

An isolation transformer essentially disconnects all shore power from your boat completely isolating your power systems and ground. To simplify, think of it like 2 lightbulbs next to each other that influence and mirror the other. Power from shore goes in and lights the one. The coily lighted part inside is so close to the other that electricity flows through and lights the other giving you power to your boat. The wiring between the two is not connected at all.

[alaskanviking]

Lots of advantages to using an isolation transformer, with the primary one being it completely isolates your boat and power systems from whatever shore power is available and other boats that have power or wiring issues and stray currents. This does not protect you from bad wiring in your boat. Another advantage is the transformer can change shore power inlet power for 120v or 240v, and you can wire the boat side to always give you 120v or 240v regardless of the inlet. I found a couple transformers. For lower power requirements – 30 amp @ 120v/16amp 240v euro – Victron has an auto isolation transformer that automatically changes between 120v and 240v inlet. They also have the standard model where you change a wire jumper around to switch. You can wire these for 120v or 240v out (boat side). I found Bridgeport Magnetics Marine isopuck transformers - approximately $1200-$1500. These are toroidal transformers (Ring) that are lighter but you have to wire a switch into the system to switch or rewire to switch between 120v & 240v. HOWEVER Bridgeport Magnetics will wind you a transformer with 3 or 4 inputs for 120v, 208v, 230v single phase (Euro) and 240v double phase (us), so that you can easily wire with a switch and select whichever inlet power you’re getting, and always getting exactly 240 or 120v out. This really sets you up for traveling with your boat as you are set no matter what system of power you hook into. Because they can do a custom transformer wiring, Bridgeport Magnetics can also wire the outlet for 230v for those euro wired boats.

2 things to remember. 1) isolation transformers do not change frequency/hertz so if you’re getting 50 hertz in your getting 50hz out regardless of the voltage. 2) some electricians will still wire the shore power ground to the transformer outlet ground. This is called a referenced ground maybe. However this completely removes the point of having the transformer in the first place and you then still need a galvanic isolator device.

[alaskanviking]

Regarding the poster with 2 separate 120v inlets. IF your shore power plugs are of 2 different phases than you can wire the transformer for 240 v and wire the L1 from the second inlet to the L2 of the transformer. You can verify this if you measure the voltage between the 2 hot wires and you get 240v (or 208v also?). BUT this will not always be the case, and really depends on the marina. In some areas both shore power cables could be on the same phase and you won’t get any power connecting them like that, in this scenario you would have to have 2 separate transformers even if you have the Bridgeport Magnetics 4 input transformer.