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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
Parents
  • 0
    Well it is an IT system -  and the advantage is that touching either live pole cannot give you a shock to ground, so a single fault live to case need not require the system to be shut down, and a double fault (both lives to case)  will simply cut the power.

    The domestic example is the UK bathroom shaver socket.

    It is not so good in a distributed system, where one piece of equipment may go live to case on pole 1, and another on pole 2, if you then pick up both pieces of equipment.

    However,  if combined with a CPC and  earth fault detection, it allow the first fault to be detected, but the system to keep running to reach a condition where it is safe to stop. This is commonly used  in situations where a dead stop might be more dangerous than keeping going.  (medical equipment, London Underground, The magnetic cranes in scrapyards,  and the wiring on some ships come to mind as examples)

    In the dark ages the fault detection might have been as simple as two lamps wired between the live poles with the centre tap earthed. When all is well, both are dim. When one side is accidentally earthed one light is bright and the other goes out, but the power can be kept on. Nowadays considerably more sophisticated equipment performs a similar function.

    Mike
Reply
  • 0
    Well it is an IT system -  and the advantage is that touching either live pole cannot give you a shock to ground, so a single fault live to case need not require the system to be shut down, and a double fault (both lives to case)  will simply cut the power.

    The domestic example is the UK bathroom shaver socket.

    It is not so good in a distributed system, where one piece of equipment may go live to case on pole 1, and another on pole 2, if you then pick up both pieces of equipment.

    However,  if combined with a CPC and  earth fault detection, it allow the first fault to be detected, but the system to keep running to reach a condition where it is safe to stop. This is commonly used  in situations where a dead stop might be more dangerous than keeping going.  (medical equipment, London Underground, The magnetic cranes in scrapyards,  and the wiring on some ships come to mind as examples)

    In the dark ages the fault detection might have been as simple as two lamps wired between the live poles with the centre tap earthed. When all is well, both are dim. When one side is accidentally earthed one light is bright and the other goes out, but the power can be kept on. Nowadays considerably more sophisticated equipment performs a similar function.

    Mike
Children
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