Electronics > Beginners
Is my Isolation Transformer not isolated?
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Electro Detective:
some photos of the unit internals would get this resolved 100% without assumptions and guesswork
ez24:
There is a good YouTube video on this.  Does anyone remember it?  I forgot
AngraMelo:
Although taking the whole thing apart might seem a good idea, Im afraid I might not be able to put everything together and even if I could I would certainly loose my guarantee. If it is necessary to answer the question Im open to do so.

To answer a few questions...

I do not need a earth connection to have a current, using the 2 phases is enough, granted it is not as safe.

The gentleman that said about states in brazil having different mains specifications, you are correct, every state is different, some are 110V with phase and neutral, some a 220V, some are 127V... crazy south america, I know...

Do you guys have more questions about the transformer that could lead us to a more precise position about it being isolated or not?

Brumby:

--- Quote from: helius on May 05, 2018, 12:42:20 am ---
--- Quote from: AngraMelo on May 04, 2018, 11:58:09 pm ---Now the tricky situation, when measuring resistance from the primary to the secondary I always get a reading, it starts around 500K and goes up gradually. It does not matter which cables Im measuring, I always get a resistance reading. How in the world is that isolated?
--- End quote ---

Even with galvanic isolation, there is capacitance and mutual inductance between the windings. The mutual inductance is what makes it a transformer and is absolutely necessary for it to work, and the capacitance is unavoidable given the constraints of transformer assemblies (the primary is wound over the secondary unless you use a toroidal design). An ohms reading that starts high and increases is caused by the capacitance (just like when you connect DC across a capacitor, current flows briefly and then stops). It sounds like your transformer is correctly isolated.

--- End quote ---

This covers the 'worrying' observations you originally posted and explains what they mean.

I'm inclined to agree - that based on what you have told us, the transformer you have is an isolated one.
Electro Detective:
If you can't take it apart for a look, then going by your measurements earlier, regardless of what power arrangement is in your locality,

and ignoring return paths, be they phase +phase, phase+N, phase+CT, phase+Earth, phase+E/N  or whatever the earth and neutral relationships are
and any other power company non standard practices/penny pinching shortcuts to make consumer and service personel lives complicated etc 

as long as you have two 'power' wires coming in to the transformer, and two wires out, with no connection/s to the transformer case or transformer body,

and the tranformer box and YOU are both isolated with rubber mats and boots from the bench/table/floor/wall,ground/concrete/plumbing/swimming pool/EARTH itself!,

then I would say it's a good bet (not a winning one) that you have electrical isolation from your mains transformer primary and output secondary,

in other words a FLOATING electrical system isolated from any Earth return current/voltage   

i.e. you have your own isolated 'power station' limited only by the transformers output capacity


But then you have to think about the next device/s that will connect to this isolation transformer, and ensure it does not 'break' the isolation,
as well as wiring faults, loose connections that initally test ok, and halfassed electrical assembly etc



Whatever you do, gloves, eye glasses and rubber shoe/boot soles should always be part of the 'circuit'   8)


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