Very good response. At least for me, as I was actually able to
understand it.

However, I do have a followup question. I recently replaced a fire
alarm system in a condo tower which had the amplifier stack, fire alarm
system, and security panel on 3 seperate hots but used one neutral.

I opened the disconnect for the ampifier stack, and fire alarm panel,
and measured from hot to neutral (0V), Hot to ground (0 volts), neutral
to ground (0v). When my assistant opened the neutral he noticed some
arcing as the security system was still live. Thus I learned about the
multi-wire branched circuits.

How would i go about knowing if a neutral is live or not? As all my
measurements above, and (gasp, I know it's not a good method) my magic
wand fluke voltage checker all showed 0V.

Thanks, JW