I was doing some routine maintenance in the Data Shed, and it gradually dawned on my that I could hear a beep beep noise, as of a machine in distress. My binaural beep-location soon tracked it down, it was the UPS that protects the router that converts the fibre optic cables from the street outside, to the ethernet that the data shed requires.
This device has two power inputs, which is a good idea for such a critical piece of kit. It means that if one power cable goes down, the router will continue to work. So I have each of those inputs on a different UPS.
I tried powering the UPS off and on again, that didn't work. So I decided to just bypass it, and connect that power input, straight to the power mains, without the UPS.
I did that, but the red light on the router was still on, indicating that it was only getting power from one source, the remaining UPS.
Which, now that the louder beep was silenced, I noticed was flashing its lights in a "help help" manner.
And then I realised that the two UPSes were on the same 13 amp power main, and that the neon light indicating power on the six-way strip, was off. Meaning, that there was no power going to the UPSes, and that explained the distress signals they were both giving me.
And then I noticed that the trip on the fuse box had gone. I still call it a fuse box, even though fuses on house supplies are long gone. So I flicked the trip, power was restored, and the UPSes stopped making distress signals.
And then I thought. I've been silly. I should not have had both UPSes on the same 13 amp mains power!
Fortunately, no harm done in this case. So I ran a power lead from another 13 amp mains supply to one of the UPSes, and now each UPS is on a different power supply.