> So let's get back to the issue. I have a simple engineering question: Why
> isn't the neutral available?

In this specific case I have no idea. But in general it allows you to locate
and intercept a load carrying wire on either side of a load without
reference to the return path.
Where supply and return are always run as a pair it SHOULD be academic.
Where they may be split, it can be useful to not need the other wire.

An example where this is meaningful in another type of application is
controlling a high level stop lamp in a car. If you can cut one wire without
reference to ground, you can place the circuit anywhere in the circuit,
without having to contend with what the manufacturers have done for ground
return.


        Russell McMahon

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