Dedicated 20 Amp circuit for my office. all new wires (12AWG) - 3 outlets and 1 ceiling light with a switch....switch and receptacles are rated for 20A.
Laser printer into one of the outlets...always on (Standby)
2 monitors, speakers, laptop going to quality UPS to another outlet.

Problem:
Not always but say 20% of the time...when I turn the lights on...the UPS protection circuit kicks in....you can hear it for 5 sec maybe .
The monitors don't dim, light doesn't dim - no sign of issue at all...just the fact that the moment I switch the light on - there is noise from the UPS as if current dropped or spiked (the units will kick in in either cases to protect the connected devices).

Wonder if there is an easy way to test the issue....if it is in fact an issue on the circuit....and not maybe something with the UPS unit itself.

I opened the switch box and checked to make sure all wires are tight...nothing lose to cause short that I can see....

thanks!

 

What kind of a light fixture is it ?
Some come on with a sharp current spike at startup.

 

A short circuit, by definition, would trip a breaker or blow a fuse.

This has nothing to do with current and had everything to do with voltage. Plug a meter into the same duplex that the UPS is plugged into and recreate what causes the UPS kicks in. I suspect you will see the voltage drop for a split second, enough for the UPS to detect it and kick in. After it sees the voltage stabilize it drops out and goes back into standby mode.

 

I suspect the heater in the laser printer is coming on and dropping the voltage.

 

Unless the op has laser printer on a outlet that switches on with the light switch, that will not be the case. The op says the UPS kicks in the moment he turns light on.

To the Op:

What kind of light do you have and how many?
I am not aware of any lights normally used on the office that has high inrush current on start up.
A quality UPS will also monitor the frequency not just the voltage. Perhaps your light is some how altering the frequency? I highly doubt this, but possible.

Did you try another outlet in the office and see what happens?

Loose wire elsewhere before the light circuit and the UPS can cause the problem as well.
Try plugging a laser printer into the same outlet UPS is connected to and see if UPS kicks in when laser printer comes on.
Check all connections (outlets, switches, any splices in a junction box), before the outlet the UPS is on.


Why do you have a UPS on a laptop? Doesn't a laptop already have battery inside?

 

Some UPSes have sensitivity settings too. There must be something causing a voltage drop, but it's possible it's minor - but the UPS is triggering anyway.

Some of them have DIP switches, others are software configurable. Might be worth seeing if you can reduce the UPS sensitivity instead of tracking down a possibly minor issue.

 

nothing to do with the laser printer....actually - this rare occurrence never correlated with the printer warming up / starting / printing. It only happens when switching the lights on.
And those are pretty standard ceiling lights...3 bulbs.

Will start investigating the various suggestions.... will be tough....since the problem is random and relatively rare....

 

If you replace the bulbs with LED bulbs, would that solve the issue? How about plugging the UPS into a EMI filtered power strip (usually sold as EMI surge protector)?

 

I would swap the light switch out and see if it continues. Seems more likely that something with moving parts would cause a random issue.

 

Just an update for those who may be curious.....

So in the same room, on the same circuit, but different outlet I had another, smaller UPS battery unit....the battery completely dried out and the unit no longer hold any charge.... of course it still works as a power conditioner / surge protector.
Since I disabled the battery output - I no longer have the strange issue with the other, main UPS unit - when turning on lights.....
Strange but so far this is the ONLY cause-effect I was able to note.