On May 25, 8:39*pm, JIMMIE wrote:
On May 25, 1:45*pm, 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

If its open without the magnet then its NO

Jimmie- Hide quoted text -

- Show quoted text -

If you have a NO switch, you can easily convert it to a NC closed
switch..Mount the reed relay with a magnet nearby to close it. Then
use the movable magnet to cancel the field from the attached magnet
when the movable magnet is in the vicinity of the reed relay. All it
takes is one little extra magnet.