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# 12 volt DC switch vs. 110 volt AC switch

coolclay
I dwindle a bit in electrical theory, building electrical equipment and what not. One thing that has always stumped me is what physically is the difference between a 12 volt DC switch and a 110 volt AC switch. They label them very clearly so there has to be a reason one can't be used for the other. Even though I have not had any problems substituting 110VAC switches in 12VDC circuits. The only problem I can theorize is that maybe the components inside can only handle so much voltage and/or amperage. If this was the case I would think the one built with higher tolerances could be substituted for the other but not vice versa. Any one have any ideas, I've looked online but never really found any closure.
coreymanshack
AC wave looks like this ~~~
DC wave looks like this -----

The hardware used with these waves are very different. DC and AC both have their uses.
ocalhoun
For just a basic switch, the only thing that should really matter is the amperage and voltage used. (More so the amperage.)
Too much current through too small a switch could cause overheating, melting, failure, and destruction. Too much voltage through a switch that wasn't designed for it might cause too much arcing, making the switch possibly break, and certainly not last as long.

The difference between an AC or DC switch for the same amperage and voltage? At a basic level, none.

There's no reason you shouldn't be able to use a 110 volt, 1 amp switch for a 12 volt, .5 amp circuit, for example, but the reverse would be dangerous and likely to fail.

This is not necessarily the same for other electrical components though! Don't get creative with it unless you know what you're doing. Take a basic electronics course, or at least read a book or website about it.
coolclay
Thanks coreymanshack, I already knew that though, but thanks.

Ocalhoun-
That was my take exactly. I just thought I would double check to back up my theory. And yes I do already know quite a bit about electricity, I am a household electrician, well sort of. I install appliances during the winter, and run lines, outlets, install breakers and what not.

I just wasn't positive because they label them very well, and don't say anything about being backward (less current) compatible.
coreymanshack
I was thinking you said power supply for some reason. But yeah, ocalhun is right.
Indi
 ocalhoun wrote: The difference between an AC or DC switch for the same amperage and voltage? At a basic level, none.

(Careful! ^_^; That may be true, but it also may not. An AC signal can be a complicated beast, and the voltage and current do not necessarily need to be in phase with each other, resulting in a lower power overall. For a DC signal, the power is just P = I × V, but for an AC signal, the power is P = I(rms) × V(rms) × cos(φ), where φ is the phase difference between the voltage and current signals. i don't know a lot about how electrical components are commonly rated, but i suspect that the required current rating for a 12 VAC 100 W switch is very different from the required current rating for a 12 VDC 100 W switch.

But more relevant here is the fact that if you assume the same power draw, the current through a 110 VAC switch will be much, much lower than through a 12 VDC switch. So you could use a 100 W 12 VDC switch in place of a 100 W 110 VAC switch, but not vice versa. In other words, coolclay was talking about - using 110 VAC switches in a 12 VDC circuit... is probably not wise.

i think you're right though - the current is the key here. Make sure you're current-safe, and everything should be fine.)
SonLight
How well the switch is insulated is an important safety consideration. For a 12 volt switch, only a little insulation is needed to protect the user and prevent short circuits. For a 110 volt switch, the handle should be well isolated from the wires, and the insulation needs to be much stronger.

There are enough differences that generally it would be wise to use any switch only in the type of circuit it was designed for, although it should be safe enough to use a 110-volt rated switch in a 12-volt circuit provided the power carrying capacity is sufficient.
jwellsy
If you're really interested and extreamly bored, try going through a couple of IEEE arc-flash calculations. The results are how many Kcalories of energy can potentialy be released and dictates what kind of Personnel Protective Equipment is required before the panel containing the switches could be opened for maintenance.
chatrack
Ac swich is designed to handle high voltage than high current... & visaversa
davidcyr2000
AC and DC switch contacts are supposed to be manufactured with different materials in order to withstand the arcing that occurs, and the resulting degradation of the switch contacts. AC circuits typically break cooler than DC circuits because the current drops to zero 120 times per second, which means arcing stops at least by the time the current goes to zero. Current in a DC circuit does not drop to zero immediately when the contacts open when there is an inductive component in the circuit. In a DC circuit, the voltage will spike when the contacts open and the arcing will be significantly more than in the comparable AC circuit. This results in more rapid contact degradation through pitting from the high temperature arc. The voltage rating only talks about insulation factor. Current rating only talks about current capacity, neither of which is related to the other. So an AC switch is NOT equal to a DC switch.
chatrack
 davidcyr2000 wrote: AC and DC switch contacts are supposed to be manufactured with different materials in order to withstand the arcing that occurs, and the resulting degradation of the switch contacts. AC circuits typically break cooler than DC circuits because the current drops to zero 120 times per second, which means arcing stops at least by the time the current goes to zero. Current in a DC circuit does not drop to zero immediately when the contacts open when there is an inductive component in the circuit. In a DC circuit, the voltage will spike when the contacts open and the arcing will be significantly more than in the comparable AC circuit. This results in more rapid contact degradation through pitting from the high temperature arc. The voltage rating only talks about insulation factor. Current rating only talks about current capacity, neither of which is related to the other. So an AC switch is NOT equal to a DC switch.

Hi davidcyr2000,

You give more in depth in this case... thanks
jetgirltaxi
 coolclay wrote: I dwindle a bit in electrical theory, building electrical equipment and what not. One thing that has always stumped me is what physically is the difference between a 12 volt DC switch and a 110 volt AC switch. They label them very clearly so there has to be a reason one can't be used for the other. Even though I have not had any problems substituting 110VAC switches in 12VDC circuits. The only problem I can theorize is that maybe the components inside can only handle so much voltage and/or amperage. If this was the case I would think the one built with higher tolerances could be substituted for the other but not vice versa. Any one have any ideas, I've looked online but never really found any closure.

I don't imagine there is any physical difference. The only thing that matters is the AMPERAGE rating of the switch. Current, not voltage, is what generates heat. 12 volt circuits certainly can pull some very heavy amps, think about the starter relay in a car engine. As for alternating versus direct current, I can't see how it matters to the switch.
menino
Yes, I agree with you'll, .... brings me back to my school and college days that AC stands for Alternating current and DC for direct current.

If you want to convert dc to ac, it is possible using an inverter, source (http://en.wikipedia.org/wiki/Inverter_(electrical)).
chatrack
I think in the question, it is not mentioned about the amount of current that has to be handeled.
cleo2010
I used a AC 110 volt light switch in a 12 volt DC car circuit earlier today. I was rigging a switch to turn on my cars cooling fan. The cars sensor was bad and it was overheating because the cooling fan would not come on. I had to drive the the car while the parts store ordered it. I hooked it up to the battery. The AC switch burned out within seconds so it would not turn off. The switch must have either started arching across or it welded something together inside. I threw that switch away. I re-rigged it with 10 gage stranded wire and a 30 amp AC breaker for the switch that I purchased for
\$4.00 from a surplus store. So DC is nothing to mess with. If there was a short it would heat up untill it started a fire. The car's cooling fan has heavy gage wire and a 30 amp breaker for a reason. My part comes tomorrow but I have to drive several places before I can get it and put it in. I'm taking the fire extinguisher with in the car just in case.
wacky531
You can Not use an A/C switch instead of an D/C one. An A/C switch is designed for A/C current. And a D/C switch is designed for D/C current. PERIOD! You might get away with it for awhile, but why in the world would you take the chance?

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