Q: How can I stop my iMac from automatically shutting down?

One last question: Is the problem I've described unusual? In other words, is it to be expected that iMacs will shutdown even if you don't want them to do so?

Okay,, thanks.

Thanks for your very informative reply. I have read everything you sent and considered it. However, I think it may be more valuable for one more technically oriented. As it turns out I already have at least three programs similar to the one you mention. I find that never use them and have been planning to uninstall them (they're just too advanced for my knowledge/ability). They contain just too much information.For duffers like me, programs like this need to have a feature that screams out: WARNING! or something similar. On a side note, I might mention that when I asked the creators/owners of the programs I installed about how to use them and when temperatures should be considered too high, it seemed as if they hadn't thought about it. One did say that temperatures approaching 200F should be a cause of concern. That wasn't good enough for me and still isn't. Thanks again, anyway.

Topher Kessler wrote:

 

I'm not saying its solely your wall power. Your Mac has a device in it called a Power Supply, which if failing may cut power to your system randomly (and eventually will). This may be spurred by poor wall circuits, so that's why I recommend trying another outlet or circuit, or even a UPS to even out any poor wall circuitry. It may also be spurred by high activity on your Mac that draws more power from the unit than usual. If the problem is from the power supply unit in your Mac, then it may continue to shut off randomly until you have it serviced.

 

There are no apps that will properly monitor this, as it's a problem well beyond the system's ability to monitor. There may be some indication in console logs about an unexpected power event, but that will likely be all that indicates such problems.

 

I'd say again keep it monitored, but if it continues despite settings changes, then you likely are experiencing a hardware fault.

I've been looking for this. I just wanted to say that your were right...mostly. When I took my computer to the Apple shop, their first idea was the same as yours. They thought that the problem originated with the Power Supply. Unfortunately, however, after calling me almost daily for several days with the message that the  necessary repairs would be completed shortly--"maybe even today"--they gave up. They couldn't get it working again. Nevertheless, it seems to me that the bulk of the problem was with the Power Supply. I've now bought another iMac.