What is NC NO connection?

[mealman]

Dear all CNCzone members~
Hello!

Well, I've been reading on the threads of limit switches, because I need to set up the limit switches and home switches for my little CNC milling machine.

A lot of threads mentioned NC and NO connection with limit switches, can someone explain what it means? I tried to google them but no answers was found.

Thanks!

[Geof]

A limit switch is a two way switch. It has one contact called the common and two others one is not connected to the common contact when the switch is not activated and this is the Normally Open or NO contact. The other one is connected to the common contact when the switch is not activated and this is the Normally Closed or NC contact.

Operating the switch just switches the connection from the NC to the NO.

[Al_The_Man]

Just to expand on what Geof has covered, NO-NC switches can also come in a variety of flavours, you can have NO or NC 2 wire (one or the other) 3 wire (as Geof explained) or 4 wire where the common is separate and they come both in one package, see the PDF attached.
Al.

[hixfixit]

A Normally Closed switch is the preferred option for limit and e-stop switches, as, if there is a fault with the wiring, (disconnected or break etc), the circuit thinks a limit has been reached and the machine will not start. A short in the wiring will render the switch useless, but in practise shorts are LESS likely than open circuits.

If a Normally Open switch is used, continuity does not occur until the switch is activated. If the circuit is broken, you won't know until a physical stop (or damage) occurs.

[mealman]

thx hixfixit

ur idea is brilliant