Isolation Transformer for Safety

dear,

just draw the schematic diagram showing mains, neutral, isolation transformer, & out put power terminals of 120v ac.

did you got the answer ?

just observe that out put is isolated from neutral ( return path.) also, between mains & the load out put, impedence is added - of tr. coil. this reduces the fault energy significantly.

thiis is how, safety is increased. But you do get the electric shock ( lesser then that without the tr. ) if you touch live out put terminals with bare foot.

The trick is to remember that when we talk about Voltage, we really should be saying Voltage difference. That (the difference) is what it takes to make current flow. That's why birds can sit on a 50,000 V wire without getting fried; both feet are at the same Voltage (or very, very near) and no current flows through them. So, the isolation transformer has a 120 VAC output, but that is ONLY in relation to the other lead. There is no relation to ground.

Hi Guest,

There is a variation on this theme and it involves there being a centre tap on the secondary which is taken to earth; under these circumstances the voltage between either of the output conductors and earth is 60 VAC. The description of such a transformer is therefore 60-0-60 on the rating plate. This form of transformer is popular with construction site temporary electrical systems for obvious reasons.

You should realise however that if your isolation transformer is connected to the mains via a residual current device (RCD) that it (the protective switch) will not operate in its earth leakage mode if faults occur on the secondary side of the isolation transformer. Therefore where as the proverbial shock protection of a 30mA RCD will work on the primary side you would not be afforded that protection on the secondary side circuits.

Massey.

Good answer, Massey. I think the guest does have a handle on the problem. I am going to get an isolation transformer eventually, 'cause they are supposed to be safer for working on electronic stuff. You will still get shocked if you get in between the two wires coming out of the transformer, I presume.

I did want to say, that on this side of the pond, I believe the RCD devices are called GFI, for Ground Fault Interrupting. Same rules would apply.

Hi mike k,

Thanks for the added info. at least you were able to get the gist of what I was saying.

Regards,

Massey.

The secondary is isolated from the line voltage (primary) it works.