Is my isolation transformer working?

[Wrinkley]

That's it really. We are currently in a marina with about 20 other narrowboats around us. All on metal pontoons and all plugged into the mains. I have an Airflow isolation transformer fitted and it just sits there, gently humming in the background. But how do I know that it's protecting my boat from those around me ? The anodes are fine, no pits in the hull and every thing looks good, but how do I know! I have a multimeter and know I am looking for stray voltage but do no where to look. Any help would be fantastic.

 

Graham

[GUMPY]

As its obviously powering your boat that part is fine.

Disconnect it and measure for continuity between input earth and output earth/neutral

If there is continuity then its not working.

If its open circuit then it is.

 

You could spend months trying to find stray voltage/current and what you do find may not be relevant.

Edited January 25, 2016 by Loddon

[WotEver]

1. Pull the landline socket out of the input to the transformer.

2. Use a multimeter to check for continuity between the earth pin on the input of the transformer and the hull.

 

If you have continuity it's incorrectly wired and therefore not working. If you have an open circuit then it's working.

 

Tony

[George94]

Provided it is correctly wired, the beauty of the IT is that if the lights are on you know it's working.

[Paul C]

Isolation transformers, basically, don't have a "fail unsafe" mode in the same way that a galvanic isolator can "fail unsafe". In fact there's 2 ways a galvanic isolator can fail, one not that unsafe though: it can fail unsafe by allowing the earth to go open circuit; or it can fail short circuitting the earth, which would mean while its still safe (because there's an earth), its galvanic isolation has failed negating the reason for the device in the first place.

[Robbo]

Provided it is correctly wired, the beauty of the IT is that if the lights are on you know it's working.

It could be correctly wired but upstream may not be, ie. shore socket has earth going to hull.

[WotEver]

Isolation transformers, basically, don't have a "fail unsafe" mode in the same way that a galvanic isolator can "fail unsafe". In fact there's 2 ways a galvanic isolator can fail, one not that unsafe though: it can fail unsafe by allowing the earth to go open circuit; or it can fail short circuitting the earth, which would mean while its still safe (because there's an earth), its galvanic isolation has failed negating the reason for the device in the first place.

I can't see how either of those scenarios could happen with a correctly wired IT, Paul.

 

The earth on the boat side is simply a N-E link, so there's nothing to fail open, and as it's not electrically connected to the shore earth there's nothing to fail short either.

 

Tony

It could be correctly wired but upstream may not be, ie. shore socket has earth going to hull.

Sorry, I don't understand this at all. If it's correctly wired then the shore socket doesn't have earth going to hull.

[Paul C]

I can't see how either of those scenarios could happen with a correctly wired IT, Paul.

 

 

Exactly! That's the point I'm making. They are failure modes of a galvanic isolator, not an isolation transformer. The isolation transformer, unless something melted or welded inside it (or it was miswired plain wrong) "does what it says on the tin" and isolates all the conducting elements from its input to output - the energy being transferred by electromagnetic flux (or whatever the correct tech term is).

[WotEver]

 

Exactly! That's the point I'm making. They are failure modes of a galvanic isolator, not an isolation transformer. The isolation transformer, unless something melted or welded inside it (or it was miswired plain wrong) "does what it says on the tin" and isolates all the conducting elements from its input to output - the energy being transferred by electromagnetic flux (or whatever the correct tech term is).

Sorry yes, I misread your post. A GI has the possibility of failing in two undesirable ways, an IT does not.

 

And yes, I believe electromagnetic flux is indeed the correct term.

 

Tony

[Robbo]

Sorry, I don't understand this at all. If it's correctly wired then the shore socket doesn't have earth going to hull.

Unless you've done the wiring yourself never presume.

[WotEver]

Unless you've done the wiring yourself never presume.

See post 3

[Robbo]

See post 3

As you said, do the tests never presume.