Size weight and cost:
Transformers are big heavy and expensive so on that basis they lose.
Reliability:
Other uses:
Summary:
Additional information:
10 Comments
Paul
"As the currents that cause corrosion are almost always less than 1 volt " That's an interesting measurement unit for current. -P-
Lou Reynolds
While I agree with everything you said in your description. You should point out that isolation transformers block both AC and DC stray currents. While it's a given that DC stray currents are the worst offender when it comes to corrosion, AC stray currents cause corrosion as well. But the main point of a isolation transformer is to prevent electrical shock hazards and the Galvanic Isolator is not designed for that purpose. The only thing a galvanic isolator does is block DC stray current.
Simonosteopath
"As the currents that cause corrosion are almost always less than 1 volt the protection is achieved, while the diodes still allow higher voltage current to pass in the event of a fault. " Shore earth and neutral are often several Volts difference and shore earth often many Volts difference to the water itself. Surely this presents a problem for a galvanic isolator?
Peter Kennedy
The shore ground and shore neutral are connected to each other at the power source (the transformer on the dock) They are not supposed to be at a different potential to each other but it is possible that if there are bad connections in the system or if you are at the end of a long dock on a hot day when all the air conditioners are running there will be a difference between them due to voltage drop in the neutral. You are correct that when this happens the galvanic isolator will conduct for part of each cycle.
Ann-Marie Foster
Metal boats, aluminum in particular, have a built in voltage to salt water as high as 0.9 volts. This leaves only 0.3 volts protection remaining. The ground connection in docks can be 10 times this amount, typically due to mis-wired boats using the ground connection instead of the neutral. AC leakage can easily exceed the traditional protection this so on each 1/2 cycle DC will be passed through the isolator and cause electrolysis. You should use a 2.5 volt isolator. Search Google for "2.5 volt galvanic isolator".
Peter Kennedy
That's a very interesting comment, thank you for bringing that up. Most aluminum boats I have come across have had an isolation transformer. I took a look at some of the Galvanic Isolators on offer for aluminum boats and it seems that none met the ABYC requirements of either being 1) Self Testing or 2) Fail Safe
Kevin McNeill
I'm in the process of rewiring my boat starting with the AC system. I'm going to use the Nigel Calder suggestion for isolating the systems using the shore power connection to only the battery charger and using an inverter to power the AC side. Should I install an ELCI between the battery charger and the shore power input and if so before or after the 30 A main breaker? Secondly, should the onboard AC ground be connected to the shore power ground and will doing so negate the isolation feature? I've just added your blog to my DIY section under good ideas, thanks.
Peter Kennedy
The ABYC requires you to connect your AC Ground to the engine block. The simple explanation is that if you sit on the engine and reach over and touch the air conditioner you want the two to already be connected so you are not the one completing the circuit. As a result of this connection your engine and propellor ends up being connected to everyone else in the marina's engine and propellor so you are all one giant battery floating in conductive salt water. That's why you need either a galvanic isolator or an isolation transformer. Galvanic currents are DC Currents that arise because of different metals being immersed in an electrolyte. The purpose of the ELCI main breaker is different. As well as being a main breaker it is also checking for fault current. This is AC Current that can electrocute a swimmer in the water. The level of fault trip is set at 30 mA. The ELCI part and the breaker part are combined in one unit and this needs to be within 10 feet of where shore power comes on board the boat.
Bob Rohwer
I had an ELCI (BlueSea PW3116) and Isolation Transformer (Victron 3600W Auto 115/230) installed on my boat when I switched to lithium. They were installed SHORE - ELCI - Transformer - Victron Multiplus 3000. Shouldn't the order be: SHORE - Transformer - ELCI - Multiplus?
Peter Kennedy
Once shore power comes on board the boat the ELCI comes first then the isolation transformer.
Charlie So
I read your reply on March 28th about the sequential order of Shore -> ELCI -> Transformer -> Multiplus -> boat AC loads Are there any additional needs or requirements for an ELCI located anywhere after the transformer? My boat has GFCI on individual outlets in the galley and head. The main AC distribution panel on-board is a standard "Main Power", and 6 separate sub-circuits each on their own circuit breakers. My other question is that ABYC has an exception for an on-board ELCI if your transformer is within 10 feet of your shore inlet. The marina pedestal 35' away has a ELCI on it. So for this situation, does the exception for on-board ELCI apply?
Peter Kennedy
The ABYC standards require you to have an ELCI on board your boat right after where the shore power comes on board or within 10 ft as measured along the wire. The National Electrical Code requires new dock wiring to have an ELCI at the pedestal, but older docks did not have that requirement and are not required to upgrade unless they are rewiring. There is no requirement currently to have an ELCI on board after the transformer, but it is good practice to fit a GFCI on any receptacles near water. On a boat all receptacles are near water. An ELCI give whole boat protection with a 30 mA trip but ELCI's give higher more localized protection of 5 mA
Charlie So
Peter, Thank you for your response. In the manual for the Victron 3600W isolation transformer, "Wiring Example 3.7" on page 8 shows a "GFCI" on both the shore power and on the outlet side of the transformer. By GFCI on the shore side, are they referring to a 30 mA trip ELCI? And on the transformer outlet, do they mean to say a whole-circuit 30 mA trip ELCI or would individual GFCI's (5 mA type) in the galley and head suffice? I read about the ABYC exception to having a ELCI on-board before the isolation transformer in your blog at https://shop.pkys.com/abyc-standards-elci If the exception holds, that says that a boat with an isolation transformer within 10' of the shore power inlet (which is what I will have) does not need a ELCI. Am I missing something? Thanks again.
Peter Kennedy
ABYC standards in the US require an ELCI on the incoming shore power supply to the boat at a maximum of 10ft away as measured along the wire, and before connecting to any equipment on board. So you need an ELCI before the transformer. This ELCI is to protect swimmers in the water from electrocution, and doesn't give any protection for those on board the boat. An ELCI has a 30 mA trip. In the US there is no requirement to fit an ELCI on the output of the transformer, as there is in Europe. However in the US it is common practice to fit GFCI's on all receptacles near water. GFCI's have a 5 mA trip. On a boat all receptacles are near water. This is not a requirement in Europe and explains the divergence of requirements and standards.
Joe Payne
I have an existing galvanic isolator (ProMariner ProSafe ZincSaver 60), that I'm guessing does not meet the failsafe requirement. I'm adding EFCI breakers between the shore power receptacles and the main panel. Does the GI and ELCI provide the same or similar protection for swimmers as an isolation transformer?
Peter Kennedy
The purpose of both the galvanic isolator and the isolation transformer is to block low voltage DC leakage current in the water with the goal of protecting your underwater metals. The purpose of the ELCI is to block high voltage AC leakage current in the water with the goal of saving lives if someone falls in the water.
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