> So how
> best to provide protection when the polarity of the line will be
> changing? Let's guess that the line length will be between 50 and 400
> feet of cat5 cable.

A 3v9 zener diode + a small series resistor?

> Also, I haven't done the calculations yet for voltage drop.

don't, use a constant-current drive.

Wouter van Ooijen

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