UPS Tripping When Toaster Oven is On - Different Circuits - Power Spike

Discussion in 'Electrical Forum discussion & Blog' started by cloves, Mar 25, 2021.

  1. cloves

    cloves Member

    Joined:
    Feb 9, 2010
    Location:
    New Jersey
    Hi all,

    Last two weeks my UPS has been momentarily tripping. I first noticed this happening when the toaster oven was on and cycling on and off, but then it happened at night when no toaster oven was on. I also noticed that the led lights on a my dimmer when dimmed low would also become less bright. All these circuits are on their own lines. Toaster oven is on a 12/2 20 amp circuit, computer a 12/2 20 amp circuit and my leds their own 14/2 circuit. House has 200 amp service. I am seeing between 239-240 volts on the main lugs. Today I tested the outlet where the UPS connects to and turned on my toaster oven in the kitchen. Sure enough I noticed that when the toaster oven turned on, I saw the outlet spike from 118v to 128v and back down 118v once the toaster oven cycled off which doesn't make sense. I then went to the main panel and tested a few other breakers. I touched the terminal screw on the breaker and one of the grounding buses and pretty much saw the same thing. Whenever the toaster oven turned on, I would see a spike on the main terminal screw to 128v.

    Does anyone have any idea what could be causing this spike? I don't think its normal for power to spike when the toaster oven turns on, if anything I should see power draw down no?
     
  2. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    If there is a shared neutral, and the toaster oven is on the other leg of the split phase power, that can normal for things on the other half to see more voltage. MWBC is your search term to read more on that shared neutral thing.

    However a 10 volt rise is not reasonable. I presume the toaster oven circuit drops by more than 10 volts. Also not right. Your neutral path probably has excessive resistance. Consider some wiring upgrades.


    Also, adjust your UPS software to not alarm on overvoltage until 130 volts.

    Some utilities set the incoming power to give 128 almost all of the time. Mine was doing that, and my UPS was beeping and switching fairly often. I was thinking under-voltage trips, but I bought a little voltage monitor that plugs into an outlet and displays the voltage in 3 digits. They have now dropped that to 124 for me.

    The reason they set the voltage as high as they can get away with is to increase power consumption by customers, but the reason they state is to keep the house at the far end of the line from the transformer to have sufficient voltage. If the house at the end of the line saw 115 when I see 125, then what they state would be right. Betcha that is not the case.
     
  3. Sponsor

    Sponsor Paid Advertisement

     
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    What messes up some people is that in reality, in the US residential space, we don't really have 120vac from the pole, it's 240 that is going through a transformer with what is referred to as a center tap. So, from one side to the other, there's 240, but halfway across, you get 120 from the middle to each end, but things are out of phase so that's why you get the full level.

    if the neutral connection is not solid, or the relative loads on each half are significantly unbalanced, it can mess with the voltages. Under ideal conditions, each branch is balanced and the curret through neutral back to the transformer cancels out. That rarely happens, though.
     
  5. fitter30

    fitter30 Well-Known Member

    Joined:
    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Check all the terminations in the panel and at the ground rod.
     
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Depending on the model, a UPS is designed to switch to battery supplied energy source when its incoming voltage drops below a certain value. The better UPS devices out there are always running off of the batteries making the ACV output, so the incoming ACV only is keeping the batteries charged. Those cost a lot more than the simpler ones that just switch sources from line to inverter outputs.

    For whatever reason, when the oven turns on, it is causing the voltage to drop. Often, that's a loose connection somewhere. Keep in mind that neutral is part of the power circuit, so both the black and white wires' connections must be solid.
     
Similar Threads: Tripping Toaster
Forum Title Date
Electrical Forum discussion & Blog Range Hood & GFI Tripping Mar 22, 2021
Electrical Forum discussion & Blog Toto K300 washlets tripping GFCIs Jun 17, 2019
Electrical Forum discussion & Blog Eaton Dual-Purpose breaker keeps tripping Feb 12, 2019
Electrical Forum discussion & Blog Main Klixon breaker on 3/4 hp 3-wire submers. pump keeps tripping Jul 23, 2018
Electrical Forum discussion & Blog Odd tripping breaker Jan 9, 2018

Share This Page