The uninterruptible power of a cat: replacing my UPS

Our cat broke my uninterruptible power supply (UPS). She’d decided to go on one of her periodic prowls to check that I wasn’t harbouring any mice, this time taking her through all the nooks and crannies at the back of my computer desk. A little while after she emerged, I heard an intermittent beep coming from the UPS: it had literally gone on the blink, its red ‘battery warning’ light flashing.

In truth, the cat was (if it’s possible) a scapegoat. Well over five years old now, the UPS battery was finally on its way out. As a replacement would cost around £/$/€ 90 by the time it was delivered, and a brand new and larger-capacity model would be less than twice the price, I opted to replace with new.

Buying a UPS is worryingly difficult. Amazon was happy to sell me one, but because I live on the Isle of Wight, it refused to ship it to me, even at additional cost. No local retailer seems to stock them: we used to have a branch of Maplin which did, until the chain went bust. But other shops which are happy to sell you desktop computers usually don’t even know what a UPS is. Neither does Apple’s store, which seems amazingly remiss.

Gone are the days when my desktop system was complex, with multiple internal disks, expansion cards, all manner of peripherals, and more. Now it’s just an iMac Pro with a single external SSD, my external RAID drive, modem-router, and UPS. And without the UPS, everything else is at risk.

We like to think that a constant and reliable mains power supply is a given throughout much of Europe, North America, East Asia, and further afield. Then along comes a really stonking storm, and everything goes dark. Here, just a couple of miles from the English Channel, it’s usually storm damage to overhead power cables, but lightning strikes and ‘simple’ failure are also not infrequent. In a city, your biggest enemy is probably that big hole that is being dug just down the road. One false move by the excavator and out go your lights and computers.

My MacBook Pro, of course, has what is effectively its own UPS in its internal battery. But other Mac systems, for all their tolerant power supplies, don’t work long when the power goes off. And if it happens in the middle of a routine backup, the damage can be very significant indeed. APFS with its copy-on-write should be more accommodating, but good old HFS+ is often badly screwed after sudden interruption, and some hard drives just die.

My old UPS had looked after my Mac and modem-router through some fairly tense times. One power cut blacked out the whole of our village, sending people we hadn’t seen for years out onto the streets to try to get mobile connections to confirm it wasn’t the end of the world. But more usually they’re when the wind is raging Force 10 or more and we’re well-wrapped in duvet, or when there’s a spectacular display of lightning bolts striking radio masts on the high downs around us.

For many years, I have bought APC models in their Back-UPS range. The new UPS is a BX1400UI, which should deliver 1400 VA or 700 W, and replaces an 800 VA or 540 W model. I’ve gone up a little to give some extra capacity for my iMac Pro, which draws between 64 and 370 W according to Apple. Add in the external RAID and modem-router and the whole system is probably going to draw 600 W at most, rather more than the old UPS would have liked.

Mains outages here tend to be brief, less than two minutes, or last longer than an hour. I’ve therefore configured my Mac to shut down once it has been on UPS battery power for 5 minutes, or the battery is down to 80% capacity. Unlike some economy UPS models, APC Back-UPS come standard with a USB port. My older UPS needed a special cable to support its non-standard USB socket, but I’m happy to see that this new model takes a standard USB printer cable, of which I have plenty.


Once you have connected the USB cable to your Mac, Energy Saver recognises the UPS and offers its special configuration settings (above) and, most important of all, Shutdown Options (below).


The first time that you install a larger UPS, you’ll need to make preparations for its connection. Although some smaller ‘domestic’ units come with standard mains-style power sockets, bigger units only offer IEC sockets like those on your Mac. You therefore need IEC (male) to IEC (female) power cables for everything that you’re going to connect to the UPS. This model comes with two cables, which is very helpful. I made myself a short tail IEC to mains socket to which I connect a four-socket adaptor for low-power systems like my modem-router.

Once the UPS has had a couple of days to fully charge and settle, I will do the vital test which so many users forget: with apps closed and no backup due, I’ll turn off the mains power at the wall and check that automatic shutdown occurs as expected. In one version of macOS not so long ago, I discovered a bug that caused this to fail in some circumstances. There seems little point in investing in a good UPS if you don’t check that it works.

Inevitably the cat had the last word on the matter. Once I had cleaned the shelf on which my UPS sits, and was all ready to put the new one in and connect it up, she jumped onto the shelf and stood in its place. She had got the better of me again.


I ran my test of the UPS and power failure on the morning of 16 December. The system worked perfectly, my iMac Pro shutting down as expected after 5 minutes on battery power, and shutting my external RAID down with it. At that stage, there was a little more than 80% remaining capacity in the UPS, so I think I have gauged my settings about right. The cat took no interest.