Electronic – Switch current rating AC vs DC


I'm looking for a high current DC switch (able to switch something like 5V@30A) and I've encountered several DPDT that might do what I need, however they are only rated for AC applications (3A@250VAC or 6A@125VAC). Are these rating convertible to DC? or is that something that only the facturarer would know?

Best Answer

AC ratings are typically much more lenient and DC much more strict because of arcing problems:

  • AC arcs tend to not last very long, and their polarity is effectively random so that the material transfer from one contact to the other pretty much cancels out.
  • DC arcs are much more difficult to stop, and the material transfer is always the same direction so as to erode one of the contacts.

So the DC specs are typically much lower than AC for the same switch. Relays are the same way.