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Galvanic Isolator


Traveller

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As you have only posted an image there are no specifications or approvals (ANAYB?) so how can we say if it is any good. What you have to watch is the maximum current it is designed to stand under fault conditions. This can be thousands of amps for a very short while.

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ABYC (American Boat & Yacht Council) approved ones are supposed to be the best, but few available in the UK, and expensive. 

 

I recently opted for a Victron one. The one above looks similar to the safeshore inline type, but as Tony said, the specifications are everything. 

Edited by rusty69
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On 13/11/2019 at 00:04, Traveller said:

Thinking of getting one of the below. Any experience of them here? Any good?

1846581257_Screenshot2019-11-12at23_59_00.png.e03e67cf80c03b30b6c9920471323788.png

I've tried zooming in on the picture and it pixelates before I can make out any manufacturer name. One thing that does strike me is that it is enclosed in a bog standard waterproof electrical junction box, with bog standard cable glands for the entry and exit cables. I'm not saying that it is, but this is the sort of construction that could be home made, or very low production run. That isn't necessarily a bad thing, but can you be sure that the person responsible for its design has taken in to account the very high currents that may have to be dissipated in a fault as @Tony Brooks describes. More likely to be properly designed if it is from a larger manufacturer. Their isolators tend to have massive metal heat sinks as part of the casing. See Victron and Safeshore. A possible reason why this one is in a weather resistant junction box is that it is for mounting outside. Safeshore do models that look similar to this for outdoor use. What is the price they are asking compared with Victron and Safeshore? It is significantly cheaper there is a reason and it may be skimping on the size and power handling of the internal diodes and their heat sinking.

 

Jen

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I would be unhappy the long term reliability of any GI that could not handle a fault current of at least 1600 amps.  One rated at 500 amps fsult current capacity would need checking every time the shore bollard breaker tripped to see if the diodes have survived.

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11 minutes ago, cuthound said:

I would be unhappy the long term reliability of any GI that could not handle a fault current of at least 1600 amps.  One rated at 500 amps fsult current capacity would need checking every time the shore bollard breaker tripped to see if the diodes have survived.

Or worse gone open circuit 

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2 minutes ago, ditchcrawler said:

Or worse gone open circuit 

 

Certainly an open circuit failure is dangerous for human beings (risk of electrocution due to lack of protective earth), whilst a short circuit failure lavea tne boat permanently connected to the shoreline earth, risking galvanic corrosion of the hull.

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5 minutes ago, cuthound said:

 

Certainly an open circuit failure is dangerous for human beings (risk of electrocution due to lack of protective earth), whilst a short circuit failure lavea tne boat permanently connected to the shoreline earth, risking galvanic corrosion of the hull.

In my opinion a 30ma RCD will operate with no earth return wire on a steel boat floating in water. I think that would be more than an adequate return path to operate the trip but i doubt it would blow a fuse.

 

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13 minutes ago, ditchcrawler said:

In my opinion a 30ma RCD will operate with no earth return wire on a steel boat floating in water. I think that would be more than an adequate return path to operate the trip but i doubt it would blow a fuse.

 

 

An RCD depends on a current difference of 30mA or more between neutral and live conductors. It doesn't need an earth connection to operate.

 

However if the GI goes open circuit, and a live conductors comes loose and touches a metal part thst would be earthed, then that metal part will become live, rather than the supply fuse or breaker tripping.

 

If someone then accidentally touched the live metal part they would get a shock, if they were also touching say the steel shell of the boat which would be connected rather poorly to earth via the water the boat floats in. Only if the current going through the person to the water was greater than 30mA would the RCD trip, so it is possible the person would get a shock without tripping the RCD.

 

If the loose live wire were to touch the hull, it would nmake the hull live, which would present a danger of electric shock to anyone standing on the bank and then touching the hull.

Edited by cuthound
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11 minutes ago, cuthound said:

 

 

However if the GI goes open circuit, and a live conductors comes loose and touches a metal part thst would be earthed, then that metal part will become live, rather than the supply fuse or breaker tripping.

 

And do you not think 30ma imbalance would occur with 50 foot of steel floating in water if a live conductor was to touch the steel work.

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2 hours ago, ditchcrawler said:

And do you not think 30ma imbalance would occur with 50 foot of steel floating in water if a live conductor was to touch the steel work.

 

Depends on the conductivity of the water. Fresh water is not necessarily that conductive.

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