All,
I remember an application where a small value carbon resistor was
placed in a circuit to handle overloads which could result in a fire. This
was reliably demonstrated to fail in an open circuit under the fault
conditions evaluated.
When, at a later date, it was discovered that fires were happening
in the equipment it was determined that an aggressive purchasing agent had
saved a few pennies a resistor by buying wire wound resistors in this size.
Unfortunately, wire wound resistors behave like a toaster under fault
conditions which started the plastic overcoating on fire which, then, set the
circuit board on fire. All of this happened long before the first item of
concern (a transformer winding) ever caught fire.
The result was that the company had to do a recall on the products
and make the proper replacement of a single resistor.
The cost of the recall was very large compared to the savings on
the cheaper resistors.
Arrrghh; the price of not understanding the details of the
application when changing things.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety Engineer
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201 fone/fax
[email protected]
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