Thanks, E., for bringing up the issue of single point of failure. Hadn't thought
about that, which makes me ask some questions about DPDT vs SPST switches.
Looking at the schematic of a DPDT switch it looks like there are two circuits,
an upper and a lower. Their terminals are separate but contained in the same
housing. They also use the same lever and the mechanism the lever connects to
that makes and brakes the contacts.
If the only way a switch failed was through these shared components, then a DPDT
would have the same reliability as a SPST, so there would be a single point
of failure.
And if DPDT's never failed at these shared components, then having one DPDT would
be just as reliable as having two SPST's, and there wouldn't be a single point
of failure.
I'm sure the truth lies somewhere between these two extremes. If it turns out that
a DPDT has 90% of the reliabilty as two SPST's, I might stick with just one
DPDT. If it has only 20% of the reliabilty of two SPST's, I might consider going
with two switches.
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Dan
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