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Curious occurrence:
Overnight some fairly severe thunder storm cells passed through my area.
Normally, if there's more than 1 or 2 seconds of power disruption, most the of electric/electronic devices without battery or other power backup crap out – the typical flashing 12:00 on clocks, for example.
Last night, however, the only item which shut down was my iMac (mid-2011 model). All other appliances seemed fine and no circuit breakers anywhere needed resetting.

Any thoughts?

I don't know if this applies to you, but my Mac would spontaneously shut down even when there was no power outage (that I was aware of, at least). At the same time, my APC UBS went bonkers. Instead of the flashing green light, it emitted a high pitched squeal. I had to manually turn the APC off and then turn it on again to get back to normal. (The same thing happened during an actual outage.)

The APC's battery read at 100% charge so I figured that that wasn't the issue. Nevertheless, when I phoned APC, they sent me a new battery and asked me to try it. That seemed to cure the problem. I have had several outages and the APC behaved as it should, with the appropriate software causing the Mac to shut down normally. BTW, my APC unit was still under warranty and APC should have charged for a new battery, but they didn't. They didn't even ask me to return the old one.

Nope. I haven't got a UBS/UPS, only a surge protector which doesn't seem to have been disturbed.

Obviously all surge protectors are not created equal. But with even the best (freely translated most expensive) are subject to wear and tear from repeated electrical events or surges. Every time a surge is blocked the components in the surge protector are subject to electrical wear and over time respond more and more slowly to the each subsequent event. So a top of the line surge protector that is more than a few years old often may not be able to respond fast enough to to block at least the leading edge of a surge from getting to your computer. If you are in an area that has lots of thunderstorms, such as central Florida the effective life span of the surge protector can be as short as a year. When my daughter was living in central Florida, she "saved money by getting cheap surge protectors and would have to replace them at least every six months of so. Her computers might last a year or so.

Point being your computer could have been hit by a surge even though the surge protector was apparently undisturbed but the duration of the incident was insufficient to cause the clocks etc. to reset.

Good point. And probably what caused the "anomaly".
Edit: It also suggests that there is (something resembling) surge protection built into the iMac. Anything to that? There was no diagnostic log info which indicated unexpected shutdown.

To your knowledge is there any simple and/or straightforward way to check out the level of protection of a surge protector?

We only get a few serious boomers during the summer; normally they just knock out a local electrical substation (which takes everything down).

As for central Florida: My sister lives there, and her refrigerator seems to require more surge protection than her iMac. Her iMacs last for just about ever.
For sake of comparison my 2000 iMac DV SE (G3) is still up and running.

The only thing I can think of would require a good laboratory quality recording oscilloscope and a device capable of generating electrical spikes. The test equipment would likely cost many times more than the cost of periodically replacing the surge protector.


That could well be a function of specific location and power company and their physical cable plant. My former son-in-law is a building contractor in central Florida and strongly encourages "whole house" surge protectors in homes he builds. That would probably significantly extend the life of your sister's refrigerators.

RE surge protection:
I just came across an excellent review article, The Best Surge Protector, in The Wirecutter (February 14, 2014).

These are very expensiveSurge Protectors http://www.zerosurge.com . Wondering if anyone is familiar with them. They seem quite good.

Indeed. I recall threads extolling ZeroSurge's quality, but that must have been in pre-FTM times, as I cannot find them here.