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johnhaslam...
johnhaslam...

Posted: Fri Jul 06, 2012 2:58pm

Post Subject: Galvanic Isolator vs Isolation transformer

Hello, John Haslam here. The marina on which we are moored is being refurbishes and will soon have electrical hook ups for all mooring.( non at present) I believe we therefore need to protect our boat to a higher level than at present (anodes fitted) from galvanic corrosion. Which device do you recommend, galvanic isolator or isolation transformer and why? What testing regimes need to be in place for such devices to ensure there integrity?

Tony-B...
Tony-B...

Posted: Fri Jul 06, 2012 3:34pm

Post Subject: Galvanic Isolator vs Isolation transformer

Dear John, if you do not bring mains aboard then you do not need either device. If one boat in close proximity to you had a short to hull type fault whilst another on the other side of you had no GI or IT then you might still suffer corrosion, but so would you if you had either device installed. If you want to bring a shoreline onto your boat then I would fit a soft start isolation transformer. Airquip seem well spoken of by those who should know but you do have to mount it in your own insulated case (plastic tool box?). However having saying what I would do is not that helpful because I will not have mains aboard the boat apart from an extension lead directly connected to a power tool. I understand that the EU may be drawing up standards for Galvanic isolators but as yet I have not heard they are completed or in place and I have not seen any standards on adverts. Again those who have studied such things point out that the diodes in a GI can be subject to many thousands of amps under fault conditions and may well be damaged in the short time it takes for a circuit breaker or RCD to trip. In such an instant you would either be left with your hull directly bonded to the mains "earth" (short circuit) or you may be left with no earth protection at all (open circuit) in which case your RCD may not work. There are also some rarer situations where GIs can be forced into conduction when they will be useless in protecting your hull. This can not happen with an isolation transformer unless it burns out because there is only a magnetic connection between the mains and your boat. I am no expert in the regulations in respect of mains equipment but it has been suggested that it may be illegal to fit a galvanic isolator (it is to do with ensuring the integrity of the "earth" wire). Some GIs come with LEDs that claim to indicate their condition but again I have heard their reliability questioned. It is not a good idea to encourage people who's electrical competence is unknown to do things to any mains circuits so I am not going to tell you how to test a galvanic isolator but I am sure the vendor will. The considerable cost difference between GIs and ITs means that some people will find it hard to justify the cost of an IT so I would say that if you are going to leave the boat connected and unattended for long period then a IT would be the safest way to go. However if you only connect overnight now and again while you are aboard then a would be a justifiable compromise. Tony Brooks

johnhaslam...
johnhaslam...

Posted: Wed Jul 11, 2012 10:47am

Post Subject: Galvanic Isolator vs Isolation transformer

Thank you Tony, I found your reply very enlightening. There is certainly a big cost difference in the two systems and I have no plans to use a shoreline for any extended periods, if a all. Thank you.

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