Author Topic: Isolation Transformer Question  (Read 1098 times)

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Offline wn1fju

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Isolation Transformer Question
« on: March 17, 2016, 11:19:43 pm »
I'm using a Sencore PR57 (variable) isolation transformer.  This one runs earth ground through to the secondary.  I thought the point of such a beast was that a voltage measurement across the hot and neutral outputs will be 120 VAC (I'm in USA), but the "safety" results from the fact that both the hot and the neutral are floating (nominally at zero) with respect to earth ground. 

Now I plug in a piece of test equipment into the PR57, say an HP piece with a line filter.  In a typical line filter are two (0.22 uF) caps from hot to earth and neutral to earth.  Does that not act as an AC voltage divider and basically place the hot and neutral both about 60 VAC over earth ground?  So where is my isolation safety if I'm touching the hot and the chassis at the same time?

If the DUT doesn't have a line filter, would not I expect the hot and neutral to nominally be at 0 VAC over earth?

Online Zero999

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Re: Isolation Transformer Question
« Reply #1 on: March 17, 2016, 11:31:04 pm »
The earth shouldn't run straight through the transformer. The appliances connected to the secondary should all be unearthed but their chassis need to be connected together.

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