[Bill in ABQ]

We have a home office that has two computers and a number of peripheral devices plugged in to the outlets that connect to a single, 15 amp circuit. Recently, the power on this circuit is somehow interrupted for a split second, then goes back on. The breaker is never tripped. This happens numerous times daily - maybe a couple of times an hour. I only am aware of it because the PC's are on UPS batteries that beep whenever there is a power interruption. It then recovers almost immediately.

Since the breaker never trips, I am wondering if there is a loose wire in one of the outlets that is intermittently losing contact. Or is there another possibility that I can check? Any thoughts or suggestions will be greatly appreciated!

[tkrussell]

First I think you need to determine all the outlets and appliances on this circuit. Then notice if any of the other devices reflect this interruption of power.

Certainly the problem can be caused by a loose connection, that intermittenly breaks connection for a moment, and then back on.

I suspect thou, the UPS alarm is possiblly caused by a voltage sag. This is where the voltage is dropping below the threshold of the UPS. It will be rated to monitor a range of voltage, possibly 10% plus or minus.

If the UPS is detecting just a voltage drop, this is the reason I ask what else is on the circuit. For example, I usually find a Laser printer on the same circuit, on the line side of the UPS but on the same circuit. Laser printers keep themselves warm by cycling on and off internally. This draw on the circuit may cause the voltage on the line side of the UPS to sag, and the UPS sees it as a voltage problem.

Lets check what all the outlets and appliances that are on the circuit before looking for a loose connection.

Check into this and get back with the results and we can go from there.

[Bill in ABQ]

Thanks for the response. Your theory makes a lot of sense - especially since I have noticed that when someone's turns on a vacuum cleaner or turns on a TV on the same circuit, the UPS alarm beeps. That supports your idea that a sudden draw of power pulls the UPS below its threshold. I will check this out and report back. The one thing that puzzles me is that I have had the same things plugged in in the same configuration for 3-4 years and yet this just started happening within the past several weeks.

To be continued...

[Bill in ABQ]

So far, you're right. I disconnected everything from the UPS except the computer (and admittedly the UPS was overloaded with a power strip plugged into it that had all but one outlet used - a no no I know but it has worked!).
I turned the TV on and nothing happened (no UPS alarm). But then I plugged the vacuum cleaner into an outlet on the same circuit and the UPS alarm sounded. I guess the vacuum draws just enough additional voltage to put the UPS over the edge.

Now I just need to see if the random UPS attacks stop. There is a printer on the circuit but not on this particular UPS (it's plugged into a different outlet with its own UPS). Everything else on the circuit is low amp stuff (phone, calculator, Zip drive etc.). If the random shutdown reoccurs, I'll move the printer to a different circuit and see what happens.

Thanks again for your help.