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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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    I'm not sure what benefit they are getting from having this as an IT system?

    I guess an IT (or separated) system has a number of advatanges - e.g. it's passively safe - i.e. it remains safe on first fault even if disconnection doesn't happen for some reason. If it's a bit like a giant scalextric set then loop impedances in general and specifically earthing of the cars might be a bit unreliable (e.g. dirt/oxide on the track/pickups) - or if the disconnection relay contact weld. Or perhaps the disconnection time wants to be longer than consistent with shock protection - e.g.to ride through transient overloads or leakage that would otherwise nuisance trip. 


    It'll likely also give some protection against direct contact with one pole (when conventional ADS wouldn't helo anyway) if say the track is exposed (but not against simultaneous contact with both poles of course).


    The transformer might also do a little voltage conversion if the setup is from abroad or intended for export.


       - Andy.
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  • 0
    I'm not sure what benefit they are getting from having this as an IT system?

    I guess an IT (or separated) system has a number of advatanges - e.g. it's passively safe - i.e. it remains safe on first fault even if disconnection doesn't happen for some reason. If it's a bit like a giant scalextric set then loop impedances in general and specifically earthing of the cars might be a bit unreliable (e.g. dirt/oxide on the track/pickups) - or if the disconnection relay contact weld. Or perhaps the disconnection time wants to be longer than consistent with shock protection - e.g.to ride through transient overloads or leakage that would otherwise nuisance trip. 


    It'll likely also give some protection against direct contact with one pole (when conventional ADS wouldn't helo anyway) if say the track is exposed (but not against simultaneous contact with both poles of course).


    The transformer might also do a little voltage conversion if the setup is from abroad or intended for export.


       - Andy.
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