Isolation Transformer

Okay.... Let's see if anyone else has any observation to relate.

Am 27.09.2024 um 12:22 schrieb Cursitor Doom:

The core was used to clean the tip of a soldering iron?

He was quite possibly electrocuted.

Earth is only required on the input side?

If used with a single appliance, yes. If the load is not known, it's safer to add the earth.

i don't quite understand that remark. Someone decided to join the two earths together, which completely bypasses the safety an isolation tranformer is designed to provide. Such a transformer is wired to remove the earth reference on the secondary side, which makes working on mains voltage equipment much safer for a repairer. There is only *one* possible explanation for this configuration I can think of (whoever did it being an idiot besides) and that is to limit the amount of energy available. Working direct from the mains there's a great deal of energy available. By using this transformer, you have galvanic isolation and also considerably limit the energy available, which means far less of a *bang* if you short something out.

yandex? are you a Commie agent?

No, it doesn't. The supply is still isolated, and has no (or a very small capacitive leakage in the transformer) voltage relative to earth.

Here is a device to send mains safely over the SMPTE hybrid fibre/copper cable in widespread use in the broadcast TV industry. it has isolating transformers at both ends of the cable. One of the safety features is that power will be disconnected if one of the mains conductors in the cable is touched, a feature which operates on this leakage which is fairly symmetric in a good toroidal isolating transformer, and at a very high impedance. The cable has an overall screen connected to the metalwork at both ends and there is a small but symmetric leakage current from either side of the output to ground, far too small to do any harm. (Maximum permitted leakage from a double-insulated device is 1mA under most standards).

If what's connected to it is double insulated, the presence of the earth is irrelevant, it won't be connected to anything. Nothing is lost by connecting the earth.

It is a breach of BBC safety regulations to plug more than one appliance into an isolating transformer, each item requires a separate transformer. The reasoning behind this is that metal bodywork could become connected to one side of the isolated supply, and in another appliance the other pole could leak to the body. If the two faulty items were connected to the same transformer, the two bodies would be connected to opposite poles of the supply, and its being isolated from earth would not make that any less dangerous. If the two items were class 1 and the earth was connected, fuses would blow when the second item was plugged in, or if the leakage was small, there would at least be no potential between the two bodies.

OK, it's unlikely, but not impossible. What is also unlikely is that the average user would be aware of the risk, whether on a building site or in a domestic garden.

A possibility.

As insults go, I can honestly say I've *never* been called a Commie in all the years I've been online! The very idea LOL!

Oh dear. Blow stuff up much do you?

I hope the BBC didn't let you anywhere near anything expensive, that's all I can say.

There probably WAS a bang at some point as the laminations on the right appear to have been melted in one place. (However, I have seen transformers where laminations have been welded together to reduce acoustic noise.) The owner might have been trying to reduce mains noise coupling into poorly designed audio equipment. John

Depends on what you are doing

I wouldn't want a soldering iron floating around when I soldered any circuitry that was sensitive to static.

Without an earth, touching any secondary wire is save. With an earth, touching any secondary and the earth is safe.

But on the mains side, where neutral is at earth potential, touching live is dangerous

I think you should stop there.

And think again

No, it isnt.

Any piece of kit standing on the ground has an earth reference.

The key is that the neutral is not tied to it. With an isolation transformer.

Only via capacitance if it's floating, the reactance of which is sufficiently high to prevent any dangerous current levels.

Neutral is not tied to what? It might make more sense if you were to explain why an isolation transformer is essential safety equipment for working on live chassis TVs or HV SMPS. What you appear to be suggesting is that it's a waste of time to use one!

And what precisely is wrong with the quoted paragraph?

Bullshit. If its standoing on the ground it will have a path to it

Earth

No. In fact I said the exact opposite. Because neither output line has any reference to earth, touching either one alone is safe , By earthing the chassis, that too is safe from any leakage

The purpose of an isolation transformer is never to limit the power., You can use a fuse for that. It's much cheaper. It's to generate two floating outputs *neither of which is referenced to earth* so you, being effectively earthed, can touch either one safely.

I used to think you had half a clue what you were talking about when it came to technical matters, but recently at least you clearly don't.

The chap who made this video is a fully qualified electrical engineer who's been making many informative contributions to the subject over very many years. Kindly allow him to spoon-feed you the details with illustrations so you can hopefully grasp the subject. I'd also invite anyone else here who's become thoroughly confused about how isolation transformers work thanks to NP to watch it and judge for themselves which one of us two is the bullshitter here:

The trouble with people with a little knowledge, is that they think they understand stuff when actually they don't. Like Climate change.

I am an highly qualified engineer who spent at least half his working life dealing with all this s*it.

Homework: Measure the resistance between either of the output terminals and earth. Think about your result.

At my first job as TV development engineer in 1966 each bench had several isolated outputs with a neon from each pole to earth. The idea was to show when the 'live chassis' had been connected to earth via a crock lead. The trouble was that the neons took 2mA, so that you got a