# What is Normally Open and Normally Close switch ? How to implement logic gates with NO and NC switch?

**URL:** <https://forumautomation.com/t/what-is-normally-open-and-normally-close-switch-how-to-implement-logic-gates-with-no-and-nc-switch/1751>\
**Category:** Industrial Automation\
**Tags:** interviewquestions\
**Created:** [February 12, 2017, 7:23pm UTC](https://forumautomation.com/t/what-is-normally-open-and-normally-close-switch-how-to-implement-logic-gates-with-no-and-nc-switch/1751 "2017-02-12T19:23:07Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![denizen](https://forumautomation.com/letter_avatar_proxy/v4/letter/d/848f3c/32.png) [@denizen](https://forumautomation.com/u/denizen)\
**Post date:** [February 12, 2017, 7:23pm UTC](https://forumautomation.com/t/what-is-normally-open-and-normally-close-switch-how-to-implement-logic-gates-with-no-and-nc-switch/1751/1 "2017-02-12T19:23:08Z")

</div>

Boolean logic is represented by two states.

True = 1 False = 0

This is also known as a digital state.

**Normally Open Switch**

State 0

 ![](https://cdn.forumautomation.com/original/1X/89be8137caaa643b994b8410a2f3e5a7e18bc9ca.jpg)

When the switch has no information or a reading of ‘false’ or ‘0’ state,then no information can be passed on to logic beyond it.You can see the gap keeps data from passing beyond.When this switch has a state of ‘true’ or ‘1’ then it close and looks like this.

State 1 ![](https://cdn.forumautomation.com/original/1X/6712ce86c658f32b9faa67420021571beb87965d.jpg)

Looking at this switch we can see that data is now “connected” across the center an logic beyond it can be computed.

**Normally Closed Switch**

 ![](https://cdn.forumautomation.com/original/1X/4f2c51018ca3fbf6d89a29d2f68a71359f0daf21.jpg)

This is the opposite of the normally open switch. When this switch has no information or a reading of ‘false’ or ‘0’ state,then the information can be passed on to logic beyond it. when this switch has a state of true or ‘1’ then it opens looks like this.

 ![](https://cdn.forumautomation.com/original/1X/642f41201a86461fff61a027d1d0e09a2cefa43b.jpg)

**AND Gate**

If A and B are ‘true’ or ‘1’ then output is ‘true’ or ‘1’.

If either A or B is false then output will effectively be stopped and be ‘false’ or ‘0’.

Two or more normally open switches in series equal to an “AND” gate.

 ![](https://cdn.forumautomation.com/original/1X/c7c7c0c3cad11b18aaf095df4b54aa5130252c24.jpg)

**OR Gate**

if A or B are “true” or “1” then the output is true or ‘1’.

If A and B is false then output will effectively be stopped and be ‘false’ or ‘0’.

Two or more normally open switch in parallel equal to “OR” gate.

 ![](https://cdn.forumautomation.com/original/1X/82984713907ec09ffeeebe0e62b0de68c914305d.jpg)

**NOR Gate**

If A and B is ‘false’ or ‘0’ then output is ‘true’ or ‘1’.

If either A OR B is true then the output will effectively be stopped and be ‘false’ or ‘0’.

Two or more normally closed switch in series is equal to NOR gate.

 ![](https://cdn.forumautomation.com/original/1X/d5eaf4beddd3e5b672ef7b67499fcc6a33f385b6.jpg)

**NAND Gate**

If either A or B is ‘false’ or ‘0’ then the output is equal to ‘true’ or ‘1’.

If A and B is true then the output will effectively be stopped and be ‘false’ or ‘0’.

Two or more normally close switches in parallel equal to NAND gate. ![](https://cdn.forumautomation.com/original/1X/9d783b4915d02a9507718808a76e2fd92d3bc3a8.jpg)

**XOR Gate**

When A and B are present we want an output to be ‘1’ or ‘true’ when only one of the input is true. If A and B are true then the output is blocked and is in state “0” or ‘false’.

If A is true then B must be false. If B is true then A must be false to have output state = ‘1’.

A normally open gate in series with a normally closed gate while in parallel with the same input with opposite disposition.