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Safety Isolating Transformers

Former Community Member
Former Community Member
I am an electrical inspector and I have come to large a newly installed machine (multiple moving parts, multiple independent motors and safety circuits) where the supply for the device is on a safety isolating transformer. This means that when I try and test the earth loop impedence for the supply I get no connection. In my mind this means that there is the potential that in an earth fault situation the device might not trip its breakers and other circuit protective devices as no fault path is generated. I have never seen an entire device protected by a safety isolating transformer and I don't know enough about them to say so I thought I would come to the experts on here for assistance! What would the advantages of this be and would there be safety implications of an installation like this?


Thanks in advance


Tom
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    tommatwalker:

    Sorry to drag this up again but I was hoping you guys may be able to give me some more assistance!


    So I have now done a lot more research into these systems and read some more standards, I believe that as per the standard I have to test the earth loop of my final circuit according to my sketch (apologies for how terrible and hand drawn it is......) but when I do I get no connection. Would I have to do this live and if so how do I do this safely? Is there specific equipment for measuring the earth loop on IT systems?

    b4572bb5774b3440d271809a4f4b0ef4-original-whatsapp-image-2021-03-23-at-13.55.35.jpg


    Thanks in advance!


    Tom


    You may like to look at Fig 9C, Appendix 9, of B.S. 7671 page 491. It illustrates the IT system.


    Z.


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  • 0
    tommatwalker:

    Sorry to drag this up again but I was hoping you guys may be able to give me some more assistance!


    So I have now done a lot more research into these systems and read some more standards, I believe that as per the standard I have to test the earth loop of my final circuit according to my sketch (apologies for how terrible and hand drawn it is......) but when I do I get no connection. Would I have to do this live and if so how do I do this safely? Is there specific equipment for measuring the earth loop on IT systems?

    b4572bb5774b3440d271809a4f4b0ef4-original-whatsapp-image-2021-03-23-at-13.55.35.jpg


    Thanks in advance!


    Tom


    You may like to look at Fig 9C, Appendix 9, of B.S. 7671 page 491. It illustrates the IT system.


    Z.


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