Isolation Transformer: 2ndary Neutral bonded to Ground or not?

[Zucca]

I  can not fully understand the difference between a grounded 2ndary neutral or a fully floating 2ndary. According to the www it seems to be a safety issue, but I can´t imagine when a current could flow between in the 2ndary neutral and ground connection. It is just always an open loop, may be through parasitic C and R?

Thanks in advance.

[cybermaus]

A current would flow if you accidentally touch a lead and thus thus connect to ground via your feet. The whole idea of a isolation is that you can accidentally touch either lead and still not feel anything.

IOW: If you connect secondary neutral to ground, you defeat the purpose of the isolation transformer and may as well directly plug into the wall socket.

[Melkor]

I think that the idea of secondary grounding comes from 3-phase transformers where is needed.
I don't see a reason for doing it to an isolation transformer either.

[cybermaus]

Correct. If you have three phase transformers, you would re-ground the secondary neutral to avoid floating by unbalanced loads.
But those are not isolation transformers. They are either step-up/down transformers, or convert between single and 3 phase. Industrial use usually.

Workbench isolation transformers: Keep them isolated!

[Zucca]

Thanks!

So now I can confirm I´m not crazy and this post is wrong right:
https://www.eevblog.com/forum/projects/design-for-an-apparatus-for-more-safely-experimenting-with-mains-powered-project/msg319780/#msg319780

[Monkeh]

Thanks!

So now I can confirm I´m not crazy and this post is wrong:
https://www.eevblog.com/forum/projects/design-for-an-apparatus-for-more-safely-experimenting-with-mains-powered-project/msg319780/#msg319780

No, that post is absolutely correct.

[Zucca]

No, that post is absolutely correct.

Woops

[G7PSK]

The reason some so called isolation transformers have a centre tapped secondary is that you then only get half the volts to ground, a system used in site transformers here in the UK 240 in 110 out and 55 volts to ground. Therefore if you come into contact with one lead and the other has gone to earth you only have 55 volts rather than 110 also if either line get earthed the trip goes where if you had a live and neutral if neutral  gets damaged you wont know until you touch a damaged live. But you cant really call such a system an isolation transformer.