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no image Monday, December 11, 2017 by Shane Maher

Isolation Transformer

I am new to automation and machine Design and i am currently designing a machine for a customer and they have asked us to include an isolation transformer in our design.

From what I understand they wish to include this to minimize earth leakage back onto their electrical network in their factory.

We have 2 no. servo drives in our design and from what i know these can sometimes create earth leakage.

I am unsure what i need to spec or how to size this transformer for our design

Any heap would be appreciated.


  • by  Rick Curl
    Hi Shane-

    As long as you know how many watts (worst case) your machine requires, it's a pretty simple matter.  Just specify a transformer that will handle at least that many watts. Bear in mind that the output voltage of the transformer will drop slightly as the load increases.  Isolation transformers are usually thought of as having a 1:1 ratio (same input and output voltage), but if needed you can specify one that increases or decreases the voltage.

    If you can provide more information about your requirements I'll try to offer some options.


  • by  Shane Maher

    Hi rick,

    Thanks for your reply.

    We will be supplying the machine with a standard 13a Supply. so I guess a 3 KVA Transformer would be suitable.

    we have also included for filters with our servos.

    do they achieve the same thing or so they have a different purpose?

  • by  Rick Curl
    Isolation transformers naturally attenuate a lot of high frequency noise, and they do a great job of eliminating common mode noise (same noise of the same phase on both sides of the line).  It generally doesn't hurt to provide additional filtering if your budget allows it, especially if you're in an environment that is not tolerant of interference.

    Assuming that your line voltage is 120 volts, a 3KVA transformer should be plenty big enough. Some servo motor drivers have a poor power factor rating, and require you to use a bigger isolation transformer to compensate, but I think you've got enough headroom that you should be OK.


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