Isolation Transformer

[wkyong]

It is a pri & sec 240v 50hz Isotrans.May I know is it necessary to bond the secondary neutral of the isolation transformer to the input earth or ground?

 

[dknguyen]

It is a pri & sec 240v 50hz Isotrans.May I know is it necessary to bond the secondary neutral of the isolation transformer to the input earth or ground?

No. Doing so defeats the reason the isolation transformer is there (so the output is not relative to earth). It's there so you can touch either terminal on the secondary of the isolation transformer and not get shocked. You will get shocked if you touch both at the same time. If you connect one terminal to earth, you will get shocked if you touch just the other end. THat's why the isolation transformer is an isolation transformer- to reference the voltage away from ground to a floating voltage so you must touch both ends at the same time to get shocked.

 

[kchriste]

Just to add to dknguyen's comments. I would bond the core/case of the transformer to earth ground for safety. You don't state your location, but here in North America, the ground wire is green and is for safety only. It normally carries no current.

 

[Hero999]

If depends on why you're using the isolation transformer. At work we use an isolation transformer to power a piece of equipment with a very high earth leakage from an RCD protected supply. The whole point is to effectively remove the RCD protection so we do bond the secondary to earth and I've stuck a label on the transformer to warn people about this.

For most applications, as stated above, you shouldn't bond the secondary to earth as it defeates the purpose of an isolation transformer.