On 11/25/2010 5:22 PM Phil Allison spake thus:

Wouldn't it be possible to have an original 4000ohm shorted to 900ohm
too?

** No.

The ratio between rated primary Z and winding resistance is never less
than 5:1 and is typically 10:1 or more.

You may have a point there.

OK, let's climb down into N. Cook's pit of bodgery and post mortem
analysis and look at this.

It all depends on the expected failure mode of a transformer, correct? Two
main possibilities he open windings, or shorted windings (or I suppose
a combination). Obviously not an open winding, so probably shorted ones.

** Shame about the third and most likely scenario - one that makes the
primary R go way high.

Think " vertigris " .....

You mean *verdigris*.

So that could happen if the insulation got nicked and moisture gets in,
corroding the wire. How does that work? Narrow the wire and increase the
resistance (eventually causing an open)?


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