When I plug in the electric kettle (1500 watts), the light on the power strip goes dim. Will this low voltage cause damage to the iMac? Other items on the same circuit are the 120vac external speakers and digital clock. Wire feeding the circuit is #12.
Currently when I use the electric kettle I make sure the iMac is powered down.
Thank you for your input.
I think hardware damage is very unlikely. A shutdown or reboot is somewhat more likely. A UPS (uninterruptible power supply) would mitigate both risks.
A bigger risk is that power loss to a desktop computer can sometimes corrupt the filesystem. Though the Mac filesystem may be power-safe, unsure.
But if the lights just dim and it doesn’t actually reboot, which it shouldn’t, I wouldn’t worry about it. Even with the lights dimming, the AC line voltage is probably 90+ volts. The power supply in the Mac only needs to convert down to 12 volts, and it can probably do it just fine. (it depends on how they designed it, as always)
#12 wire should be able to handle that kind of load without a huge voltage drop. Any idea what the voltage is actually dropping down to? I think you may have a problem other than just overloading, like possibly a weak connection somewhere.
I have no idea what the specs are on your iMac, but most computer power supplies these days are designed to handle voltages all over the world, so they will typically handle down to about 90 volts or so (because Japan uses 100 volts, at least in parts of it, and you need some wiggle room on the low side, so 90-ish is a good number) and up to about 250 volts or so (for all of the 240 volt countries).
A severe brownout can cause fans to spin slowly, which can lead to overheating.
I’ve also had a lot of problems with disk drives over the years due to brownouts, though none fairly recently so I don’t know how sensitive they are these days. When our company was in a different building that often had brownouts, I ended up losing 3 disk drives in 5 years.
HFS+ (unless it’s a super-old computer from < 2005) is journaled, so that offers a bit of guarantee that the filesystem won’t end up in an inconsistent state in case of sudden computer outage.
It doesn’t guarantee though:
Unplugging the iMac is a good idea.
Installing a cheap UPS on it would solve the problem sufficiently to not worry about it any more. You can get the smallest battery available, all you’re interested in is the power conditioning feature.
Unless the breaker actually blows and kills the power completely, slightly dim lights shouldn’t cause it to lose power. I’d at least test it.
Actually modern disk drives won’t corrupt a write in progress due to power loss. In the event of power loss, the spindle motor temporarily acts as an electrical generator, using the rotational inertia of the platters to provide power to finish the write and (sometimes) to park the heads, if parking isn’t done by a spring mechanism.
A UPS also provides line conditioning which would isolate the PC (and anything else plugged into the UPS) from brownouts or spikes on the line. Not a bad idea to at least provide peace of mind, even if it’s not 100% necessary.
Sometimes. There’s write buffers in RAM that may not be empty. Even if the hard drive itself finishes a task, if you were in the middle of saving to a large file, that file’s state would now be corrupt. (since it would be half new, half old). Sometimes. I think there’s ways to perform such a write where you get atomicity from the file system.
You’re referring to Blakeyrat’s item #1 (“queued saves are all there”). I was responding to their item #2 (“hard drive creates an error on the disk” that is not recoverable by software). Old drives could just stop writing in the middle of a sector when power failed, leaving one corrupt sector, but I know that even as early as 1998 drives were using the motor-generator trick to avoid that.
And I’m talking about at a higher level, in an application. I suspect that power-safe saving is not guaranteed if you are dealing with large files and sloppy about how you tell the OS to go about doing it.
I’m not sure I’d 100% rely on that, but it’s good to know that modern drives are more reliable.
It’s called “journaling”, and yes macOS has it. (Unless, like I said above, it’s an ancient version.)
I already did a bullet point on that.
Note that while journaling will prevent corruption of the kind you spelled out above, it won’t guaranteed that all write buffers are on disk if the computer loses power. All it guarantees is that only completed write operations are on the disk; partials are thrown away.
If a software application is doing two writes, one of which puts the file into a corrupted state (but the OS/filesystem has no way of knowing that) and one of which then later fixes the corrupted state, yes, journaling won’t help you in that screnario.
But that scenario only exists because you’re running some really shoddy crappy software. 
Journaling is one way to ensure filesystem consistency, although it adds overhead to each write operation. A filesystem that I wrote (which was used in Comcast DVRs for many years) used a simpler scheme of careful write ordering to ensure consistency, which didn’t incur any extra write overhead.
BTW, there are two levels of possible consistency here – the first is simple metadata consistency, so that after a power interruption, the file system is can still be accessed, and you don’t get told that a directory is corrupt or even worse, the whole filesystem is corrupt. A more stringent level of consistency is that application data is intact. As Blakelyrat says, that can’t be done by the filesystem alone, it requires the application to be written with that type of consistency in mind. Normally that’s done by providing transactional APIs that the application can use, so it can say “start transaction; write these 12 blocks; end transaction” and the FS ensures that after an interruption at any point in time, either the 12 blocks are all written or none of them are written.
I would be concerned that a 1500 Watt kettle affected anything else, especially such a low power item as a computer. I am not an electrician, but I think you have a fault somewhere.
Is the kettle also plugged into the power strip? What size cord feeds the power strip in that case and how long is it? Does the light just dim and return or does it stay dim the whole time the kettle is heating? If the latter, there has to be a wiring issue. A household supply should not be drawn down with a relatively light load like this. Something is choking off the current. That something, like a loose or corroded connection, is generating heat. This problem will sort of go away after the place starts on fire. I wouldn’t be making all day chili in that pot.
Funny. Yeah, the OP should check the receptacle the kettle uses.
Thank you everyone for your replies.
I have orderred a UPS. A cheap solution that will also help with other scenarios.
Again thank you for your help.