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I was looking to make a custom button to power my PC (I needed something which was a bit more custom than the traditional push buttons for PCs (it's not important)) and I came across these: https://www.amazon.co.uk/dp/B0825JMH6F/

I can see they're momentary switches and (I'll be attaching headers to the end of the wires so they go on the motherboard) but the description says, "AC 250V 3A", and since I'm not really an expert, I just want to find out what this really means. As in, if I bought these would they "blow up" the computer, or are they perfectly safe to use and I'm overthinking things?

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    \$\begingroup\$ It's a simple mechanical switch (meaning a mechanism that makes two pieces of metal touch when pressed), so there should not be a concern of damaging the computer (after all, you're only switching the small voltage that it uses to detect the switch being pressed). It being rated for 250 V/3 A just means that it's built with enough clearance to withstand 250 V without leakage or electrocuting the user, and with thick enough wires and metal that it won't overheat or melt if you tried to pass 3 A through it. \$\endgroup\$
    – nanofarad
    Commented May 6, 2021 at 15:12
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    \$\begingroup\$ Thank you, that really helps! \$\endgroup\$
    – Daniel Morris
    Commented May 6, 2021 at 15:42
  • \$\begingroup\$ Just note that using switches/relays (anything with metal contacts) far outside of their intended operating conditions, could eventually lead to issues. This has to do with the engineered traits of the contacts themselves - dimensions, contact pressure, distance, plating constitution, etc. All these factors favor certain conditions. A switch will matter little, but a relay or other type of switch which activates often can suffer from "missing contact" after a certain large number of actuations. \$\endgroup\$
    – rdtsc
    Commented May 6, 2021 at 15:52

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The "AC 250V 3A" rating is the maximum that the switch can handle.

If you would use such a momentary button:

enter image description here

and connect it to the PC's motherboard then the switch would need to handle about 5 V at a very small current. This is a lot less than 250 V and 3 A so the switch can handle this perfectly fine, nothing will blow up.

I don't think you intend to do this but I'll mention it anyway: You should NOT connect this button to the AC mains power for safety reasons!.

So: connect to the PC's motherboard will work perfectly fine.

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  • \$\begingroup\$ Thank you, that really helps, I just wanted to double check things first, I had a feeling it might've been a maximum, but better to be safe then sorry. \$\endgroup\$
    – Daniel Morris
    Commented May 6, 2021 at 15:43
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The difference between AC and DC switches is the contact rating inside. AC voltage basically goes up and down past zero, so if there are any electrical arcs they extinguish themselves when the voltage crosses zero. DC stays constant, so any electrical arcs will just keep going. You can use them interchangeably but DC switches will have better contacts.

For your application you don't need to worry about it. The switch will be momentarily closing a 5-12 volt DC signal from the motherboard, at most a few milliamps.

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