Hi Mike,

Well, I can think of some design mistakes which could lead to a
resistor failing with a lower resistance than nominal. For example,
some small resistors have a maximum working voltage lower than what
you would expect based on power dissipation (200 to 250V for 1/4W thru
hole carbon film resistors). If you exceed this, I would imagine that
you could get arcing across part or all of the resistor. Also, if the
resistor overheats and burns material around it, any carbon-containing
material around it might be able to conduct once it burns.

Yes, those are a bit of a stretch, so I suppose that you are correct.

Sean

On Sun, Aug 24, 2008 at 3:30 PM, Mike Harrison <mike@whitewing.co.uk> wrote:
> On Sun, 24 Aug 2008 14:53:25 -0400, you wrote:
>>Also, I'd want to use more than one current limiting resistor in
>>series. That way, in the unlikely event that one fails shorted, at
>>least the others are there to limit the current.
>>
>
> Resistors don't fail short - even the standards for Intrinsically safe equipment for use in
> flammable atmospheres state that resistors can be assumed to be infallible as regards failure to
> lower values.
>
> however using multiples in series helps spread heat load.
>
>
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