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I want to attach a switch to a 5 Volt battery pack to be able to turn it on and off. The batteries will power 4 DC motors. The current draw will be about 1 Amp. The switch I have is like the one here. It says 5 Volt and .3 Amp. What are the dangers of using that switch? What can happen?

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Figure 1. 1-pole, 2-way slider switch.

The worst that will happen is that the contacts burn out (open-circuit) or short out (weld closed). The maximum current they can handle is usually determined by the contact area and, but especially in this case, the contact movement speed and gap. In a good switch the contacts will toggle; that is, as the switch lever moves the contacts stay in the original position until a certain point is reached, the mechanism toggles and the contacts quickly change state. This minimises the time spent in arcing.

In the case of this switch the contacts move with the speed of the user's switching action as they are attached to the slider. It's possible to park the slider in a position where the contacts are barley made.

In short:

  • The voltage rating is the specified maximum voltage it can safely switch. (Higher voltages require larger contact separation.)
  • The current rating is the maximum current it can handle. This needs to accommodate both the continuous current through the switch when closed and any arcing during opening.)

A switch should meet or exceed the requirements for the application.

Having said all that, if you already have the switch and this is a hobby application then go ahead and try it. For intermittent use it should be fine. If you have several you could put one in each motor line.

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    \$\begingroup\$ Real worst case involves smoke and flames - the plastic could catch fire, especially if it's hot enough to weld shut. \$\endgroup\$ – Bob Aug 29 '16 at 3:52
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A 5V 1A supply isn't likely to do anything serious (though the life of the switch may be reduced), but this is why switches have current and voltage ratings:

https://www.youtube.com/watch?v=z0QhkuGClMw

Once the arc has formed, the current is flowing via charged particles (ions) in the air, and that can continue indefinitely so long as the electrical resistance of the ionized air generates enough heat to maintain the arc.

Eventually, something else will fail (or burn away) sufficiently to break the circuit, but your house may be on fire before that happens. Because the ionized air has significant amount of electrical resistance, the total current in the circuit may not be high enough to blow the main fuses in your house supply, even though it can generate enough heat to start a fire.

Note, the maximum ratings for a switch are usually higher for AC current (sometimes by a factor of 10 times) than for DC, because the AC current falls to zero twice in every cycle anyway (i.e. 100 or 120 times a second at mains frequency), and that tends to stop the arc within the first few milliseconds - but if it continues longer than that, the air temperature will be high enough to restart the arc when the voltage rises again.

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