Transformer blowing fuse

[Hornyskunk]

Anyone understand why this is happening?

I recently bought a 2000w step-down transformer to use with 120v electronics I brought from the US.

With the transformer off and nothing connected to it, I tried plugging it into an outlet at my condo. When I did, the outlet loudly and visibly sparked (once) and the transformer blew its fuse (also loudly). Meanwhile, the circuit breaker for the room tripped.

The transformer was the heaviest and most expensive that I could find at my local Amorn. This actually happened twice. After the first time, I exchanged the transformer for a new one and tried again with the same results.

I wonder if it is a problem with the wiring at my condo, but I doubt it. My condo is not exactly cheap and it was very recently built (2 years ago) in downtown Bangkok.

With the second transformer, I had the store test it before I took it home and it worked. Neither the first nor the second worked after blowing the fuse. The outlet seems to be fine, though.

Any ideas? Thanks in advance.

[Crossy]

If it blew its internal fuse are you sure you connected it / configured it correctly?

I would suggest that you may be connecting the 110V winding to the 220V supply, but without seeing the transformer couldn't be certain, can you post a photo?

EDIT Do you have a means of testing the voltage at your outlet, just to be sure? If you plug a regular tungsten lamp into the outlet is all OK?

[gandalf12]

If it is a toroid type transformer you will need a slow blow fuse. The in rush current for a toroid type is high and overloads the fuse

[Hornyskunk]

Attached are some photos of the transformer, including the blown fuse.

[Hornyskunk]

If it blew its internal fuse are you sure you connected it / configured it correctly?

I would suggest that you may be connecting the 110V winding to the 220V supply, but without seeing the transformer couldn't be certain, can you post a photo?

EDIT Do you have a means of testing the voltage at your outlet, just to be sure? If you plug a regular tungsten lamp into the outlet is all OK?

I connected the transformer with the switches in the same position as in the picture above. It should have just worked.

I don't have any means of testing the voltage and I don't own a lamp, sorry. However, the outlet continues to work for a TV, a gaming PC and an Xbox One. Those weren't plugged in at the same time I connected the transformer, though.

I will return to Amorn tomorrow to exchange the transformer again. This time I think I will go for three 500w transformers of a cheaper brand. I remember that those were a lot smaller, lighter and did not have a ground plug.

[Crossy]

That fuse isn't blown, it's annihilated

All the signs of a dead short. As to why, who knows. It's also worrying that the unit didn't work when the fuse was replaced, if it was a simple overload or switch-on surge it should have.

Can you read the value off the fuse, it will be stamped on the end cap xxA 250V or something of the same nature?

With no test gear and no lamp (?) I'm not sure how to proceed, the retailer is going to stop replacing units for you eventually.

See the new one work in the shop, change nothing, try at home. If you have the same issue again you need the help of a competent sparks, there is something awry either with your outlet or with the transformer (could be a common manufacturing error).

[lopburi3]

Is the store actually plugging it into a grounded outlet?