Limit Switch Working
May automatic device weather consumer appliance or industrial devices, these types of switches use for safety or processing purpose.
In earlier my repair jobs about soap dispenser device, I found one confusing thing where on PCB pin no. 2 is grounded where Pin number 1 is Vin. Practically when we check the switch using multimeter on beep mode for continuity in ideal position (Switch is Not pressed) it showing continuity between pin no. 1 & 2; and when we press the switch this connection to pin no.2 becomes open circuit & we get continuity between pin no. 1 & 3. But as per the Connection on the PCB Pin no.1 is Volt in & pin no.2 is grounded so it creates shorting so how it actually works. To clear that doubt I Opened one similar switch to understand the working.
The internal contact connections look like this.
As seen in the image above, when the switch is not pressed, pins 1 and 2 are connected; however, as soon as the switch is pressed, pin 1 connects to pin 3, and pin 2 becomes open. In this configuration, pin 1 serves as the common voltage input, while pins 2 and 3 act as separate outputs as per requirement. but we can use this switch in many way as per our requirement.
Now come to the point; Regarding the doubt I raised in the previous article: Pin 1 was the voltage input and Pin 2 was the ground. So, when the power line comes into direct contact with the ground, a short circuit occurs; how does it work in that scenario?
When I traced the PCB I had obtained, the pins of that switch were utilized and connected in this manner. Pin no. 3 is used as Voltage input
Pin no. 1 is used as Output &
Pin no. 2 Is Ground.
The input at pin no.3 is left ‘floating’ (open) so that pin no.2 (ground) never comes into contact with input pin no.3.
In this way, the manufacturer had used this switch differently, depending on the device’s requirements.
This article was prepared for you by Yogesh Panchal who works as a Computer Hardware Engineer in Mumbai India.
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Note: You can check his previous repair articles on ACER Laptop Repaired For Intermittent Power Problem
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Ronny
August 8, 2026 at 10:48 am
You see corrosion like that in the microswitches on soda vending machines because of the moisture.
Yogesh Panchal
August 9, 2026 at 7:50 pm
Thank you!Ronny
you are right atmosphere here is very humid that cause the oxidation.
Parasuraman S
August 8, 2026 at 3:20 pm
Oh! Great investigative report! Very useful! I think my answer to your query in the concerned article was right, correct? Many thanks for sharing this useful article.
Yogesh Panchal
August 9, 2026 at 7:51 pm
You are right Sir,
Albert van Bemmelen
August 8, 2026 at 4:39 pm
From this article I guess you tried to explain that there are 2 types of limit switches. Although to me they simply always all are changeover momentary switching switches. And also exist as horizontal or vertical limit switches. We every day even use them in our computer mouses to control our laptops or desktops. They only differ in the way we use them depending on how they are wired. Being already connected without pushing the limit switch, or used as make switch after pushing the limit switch.
Yogesh Panchal
August 9, 2026 at 7:53 pm
Right Albert,
Sometimes I see a single switch handling two different switching processes.
Anthony Paterson
August 8, 2026 at 6:29 pm
Yogesh,
it was YOU who said the 'Voltage-In'was grounded, when in fact it wasn't! In a microwave the safety interlock has a fail-safe arrangement where Line & Neutral are shorted to blow the supply fuse and ensure the safety system is restored to it safely working condition. Micro-switch es are indeed a useful and versatile component. An opened switch to show it's inner working makes it's function very easy to understand.
Yogesh Panchal
August 9, 2026 at 8:02 pm
Anthony Paterson,
Often, we think one thing, but the reality inside is different.If I hadn't taken the switch out to understand the circuit, I wouldn't have understood it at all; perhaps the technician last time didn't try taking it out to figure it out.
Mark J
August 9, 2026 at 2:43 am
Good article Yogesh.
Yogesh Panchal
August 9, 2026 at 8:03 pm
Thank you! Mark J