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Dean Hoffman[_7_]

wrote:
Another thread discussing whether a switch in something was normally
open or normally closed reminded me of a similar question I have.

If I want to buy a reed switch/magnet pair to use as a door or window
contact in an alarm system and the system requires that the contact be
closed when the window or door is closed, do I buy a N.O. switch or
N.C. switch? I assumed N.C. until I started to over-think it. A
normally open switch is one that is open until it gets activated. Reed
switches are activated by the magnet getting close. So, a normally
open switch would be closed when the magnet is near and that happens
when the window is closed - which is normal - so normally, a normally
open switch is closed - aaaaaargh! I need a replacement switch a few
months ago and ended up paying extra for a double throw switch. It
wasn't labeled so I still don't know if I wanted N.O. or N.C. I just
used the contact that worked.

So, what is "normal" for a reed switch? When the magnet is near or
not?

Pat

Normal is when there is no outside force acting on the switch,
relay, contactor, whatever.
In this case, it's when the magnet is away from the switch.