Switch question

[jasonck08]

I have a 5amp 125V switch and was wondering if its ok to run it at 10amps @ 12v's. Twice the amps 1/10th the voltage. Overall wattage would be only 120W when its rated at 625W (5Ax125v).

Too me it seems like this would be no problem, but I don't know that much about electricity... What do you guys think? :twothumbs

-Jason

 

[Raymond]

I think your thinking is wrong

Point is: there is no voltage "over" the switch, if there where, the switch would melt in an instant. That voltage rating is for isolation purposes only, so your switch can be used for (american) household voltage switching.

The current rating is the most important one. So you can only switch 5A with it, not more. A switch has a very low internal resistance, and thus a little heat is developed inside the switch. The amount of heat can be calculated with P=I²*R (p: power, I:current, R: resistance). As you can see, the current is squared.
Effect of doubling the current:
Let's say that the resistance in the switch is 0.05ohm.
rated capacity of switch:
P=5²*0.05=1.25W
double the current:
P=10²*0.05=5W

As you can see, the amount of heat that's developed inside the switch increases 4 times. That would kill the switch really quickly.

in short: Don't try to switch 10A with a 5A switch

 

[jasonck08]

Thanks a lot Raymond, will look for a 10A switch then...

 

[Raymond]

Good luck

I noticed that I cut a few corners with some remarks above:
I said that the switch is suitable for (american) household voltage switching, that is assuming that the rating is for both AC and DC.

Also, I said that the voltage rating id for isolation purposes only, that's not entirely true: There's also the phenomenon of "arcing". Most switches work by making contact between two metal surfaces. When voltages get higher, the chance of an electric arc jumping between the two contacts increases. This creates an isolating layer on top of the contacts, making the switch less reliable and increasing resistance. The voltage rating also applies to this concept. So a switch rated for 12V used with 125V could be perfectly safe from an isolation point of view (meaning you won't get electrocuted), but could wear down quickly from electronic arcing inside the switch.