Another stupid question from me... If an AC/DC adapter (cheapo wall wart) is stamped with "600ma" does that mean it has circuitry to prevent it from putting out more than 600ma, or does it mean that I had better make sure I have sufficient resistance in my load to not draw more than 600ma?

 

It means that the device should be able to supply its rated output voltage while connected to a load that draws 600mA. It the load is such that more current is drawn the output voltage likely will reduce proportionately and very possible the internal temperature would also rise possibly causing catastrophic failure. What it has to limit output current is simply the device internal resistance. It is the users job to not connect it to a load that draws more than it is rated for or be ready with a fire extinguisher.

 

To reiterate, ratings simply indicate the maximum amount you can safely put through or across a component or device. Exceeding predefined ratings causes problems, ranging from a simple failure to a major safety hazard.

The danger depends on whether the failure results in an open circuit or short circuit. An open circuit scenario is usually less dangerous than a short circuit condition, since an open circuit has no load. However, open circuits can be dangerous if the person touches the hot end thereby causing the circuit to change from an open to closed, using your body as a path to ground.

Bottom line: do not exceed ratings!

 

Good job, AutoNub. See one, do one, teach one.