The IET is carrying out some important updates between 17-30 April and all of our websites will be view only. For more information, read this Announcement

Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 3 replies
  • Subscribers 35 subscribers
  • Views 2458 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

Isolation transformer

MrJack96

I’m trying to get my head round isolation transformers and if I’m overthinking Joy. I understand the secondary isn’t earthed on one leg therefore the a shock cannot be received if on leg of the transformer was touched when in contact with the ground. But if one leg was to become accidentally earthed we then have reference to earth. Now the supply is not isolated from earth- on the second fault to earth I can understand if the fault is of low impedance the fuse should blow but if not it can then sit at a potential.

I think I am overthinking this but what do the regs say? 

many thanks in advance for your help getting my head round this topic. 

Parents
  • 0

    With an isolated supply the both ends of the windings are "floating", that is they are not linked to earth or anything else, so they could be at any voltage. The winding might have an output of say 230V between ends.

    If you catch hold of one end, and there is a path to 0v through you, then you "tie" one end to 0V, Therefore the other end will have 230V on it. 

    Let go and touch the other end, again the other end goes to 230V, your end goes to 0v.

    Only when you touch both ends of the windings will you get a shock. 

    This obviously, greatly reduces the risk of shock, even more so if there is no path to earth within reach.

    The use of isolation transformers and earth free areas was a method of reducing shock risk before RCD's (and their predecessors) became so effective and low cost. I worked in such an area around 1980.

Reply
  • 0

    With an isolated supply the both ends of the windings are "floating", that is they are not linked to earth or anything else, so they could be at any voltage. The winding might have an output of say 230V between ends.

    If you catch hold of one end, and there is a path to 0v through you, then you "tie" one end to 0V, Therefore the other end will have 230V on it. 

    Let go and touch the other end, again the other end goes to 230V, your end goes to 0v.

    Only when you touch both ends of the windings will you get a shock. 

    This obviously, greatly reduces the risk of shock, even more so if there is no path to earth within reach.

    The use of isolation transformers and earth free areas was a method of reducing shock risk before RCD's (and their predecessors) became so effective and low cost. I worked in such an area around 1980.

Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines