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I have a very basic toggle switch rated for 30 VDC and I need it for a 20 mA @ 36 VDC application.

According to the datasheet, it's rated for 6 A @ 125 VAC, 3 A @ 250 VAC, and 4 A @ 30 VDC.

In the AC rating, 6 A x 125 V = 3 A x 250 V. Can I make this same calculation for my DC application, meaning that 4 A x 30 VDC = 3.333 A x 36 VDC?

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For this particular switch, it is more than capable to insulate 36 V. But, for a switch, it is much harder to quench DC once flowing than it is for the case of AC, hence the lower DC rating. But as your current is low, and the voltage only mildly exceeds specs, it is gonna work fine because the potential arc will be not very intense.

However, if you have to rely on it and if you need some legal fallback grounds for debates with insurance companies, neither my nor your word is going to cut it. You'll have to use another part which includes 36 VDC in its specifications.

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At a practical level, if the current is definitely limited to 20mA then it should be fine. The insulation will hold (given the AC rating), and the current limit should prevent the issues with DC arcing which occur at higher currents.

Having said that, if your house burns down as a result of an electrical fault with this switch, then your insurers might well not pay out, and you would probably struggle to force them to do so through the courts.

Your call, but I'd strongly recommend a different switch if it was in a device to be used by or sold to others. (For a non-crital application for personal use, I'd have no concerns.)

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No, absolutely no! Rated voltage is absolutely independent from switching power. Rated voltage is tied to isolation and higher voltage can cause human damage!

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  • \$\begingroup\$ One of the issues with switches (and relays, for that matter), is that when they break (open up), an arc is drawn between the opening contacts. This arc erodes the contacts and over times leads to failure or intermittent operation. When switching an AC signal such as 115 VAC, the arc is extinguished when the voltage cycles through zero, which reduces the rate of contact erosion. The DC condition is also worse because the contact material always erodes from the same contact when opening. In an AC application, the material erodes and, to some extent, re-deposits on each contact equally. \$\endgroup\$
    – SteveSh
    Apr 2, 2020 at 15:51
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    \$\begingroup\$ "higher voltage can cause human damage". True sometimes, but not in this case. The difference between 30 VDC and 36 VDC is minor in so far as human safety goes. You really don't have to worry much in most applications (medical devices may be different) until the voltage gets above 48 VDC. \$\endgroup\$
    – SteveSh
    Apr 2, 2020 at 15:55
  • \$\begingroup\$ @SteveSh You are right. But cause of an arc is the current. You don't nee high voltage. Welding devices work with low voltage. You are right, too. But in an other thread I was reprimanded because I answered a question not universally. Potential of damage was low (burn fingers by resistor driven by battery). Electronic devices built with tolerances, so 20% overvoltage will probably not damage device or human but you should be form a habit of taking correctly rated devices. \$\endgroup\$
    – Findus
    Apr 2, 2020 at 16:08
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    \$\begingroup\$ @Findus can you strike an arc with 36vdc and 250mA? don't think so - at least 80vdc based on all the welders and welding I have done... \$\endgroup\$
    – Solar Mike
    Apr 2, 2020 at 17:40
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    \$\begingroup\$ @Findus Please clarify your answer. The phrases "rated voltage is addicted to isolation" and "can cause human damage" are very vague and unscientific. \$\endgroup\$ Apr 2, 2020 at 20:13

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