So it appears that I narrowed down the cause of my Random Flickering- the faulty 20-amp circuit on the detached garage service panel (leaking 60 volts at some point between the breaker and the last outlet). Once I kill that breaker, all of my random flickering seems to have stopped (and that breaker will not be turned on until that branch is either re-wired, or a specific cause is found).

However, now I have noticed a slight dimming whenever the A/C, Fridge, or well pump/pressure tank kicks in. From reading around it looks like this slight dimming tied to major appliances kicking in is not something to be too concerned about. And when it comes to the Fridge and A/C, it isn't an issue for us. Where it does get quite annoying is with the well pump/pressure tank. Whenever water is running (doing dishes, laundry, taking a shower, etc..) the pump kicks in every 10-15 seconds or so, giving the whole house a nice 10-15 second "beat" of lights dimming. Is there anything I can do for this one appliance circuit to reduce or eliminate the flicker?

  • 1
    You might need a service upgrade.
    – Tester101
    Commented Sep 12, 2010 at 4:19
  • Aftermarket "soft start kits" are marketed for a/c condensing units. The claim is that this more gradually spins up the compressor and so reduces the maximum instaneous current. I don't know if these really work, but if they do, couldn't one of these be used on a water pump? Commented Jan 24, 2022 at 23:35
  • brighter under load is a bad neutral connection at the transformer. Brownout under load is lack of capacity.
    – Mazura
    Commented Jan 25, 2022 at 4:08

1 Answer 1


Think of the electricity flowing into your house just like water flowing through a pipe. If you turn on a faucet only halfway then you will probably not notice a drop in pressure elsewhere in the house. But if your washing machine is filling (or your irrigation system kicks in, etc.) then you will see reduced pressure elsewhere in the house.

The electricity in your house works the same way. Air conditioners, refrigerators, water pumps, draw a lot of electricity when they first start up and you may see a drop in "pressure" when any of those items turn on:

Air conditioners, refrigerators, freezers, furnaces, etc. that have large motors require enormous amounts of power when the motor first starts to spin up to speed. Once the motor is spinning, the energy requirement drops way down. This instantaneous need for motor shaft speed is what causes that momentary dimming of your lights.
Reference: http://www.askthebuilder.com/QA_Lights_Dim_When_AC_Comes_On.shtml

As @Tester101 mentioned in the comments, you could look into a service upgrade to your house (which might not be a bad idea) but the problem might also be with your water pump. The pump kicking on/off every 15 seconds may indicate a problem with the pump itself (capacitor or pressure leak) or possibly an incorrectly sized pump for your usage. You probably want to look into a new/repair/upgrade of the water pump.

  • Thaks Jeff- it turns out there was indeed a problem with the well pump system- the pressure tank was water-logged. I recharged the tank, and all is now well. That being said, I am still curious to know if there is any sort of device (similar to a UPS?) that can keep some of the spiked startup load of a motor from affecting the system so much. I have a 200amp service, which I thought would be sufficient for the pump or fridge.
    – MarkD
    Commented Sep 12, 2010 at 20:04
  • A UPS (uninterruptible power supply) will supply power when the electricity in your house goes out. What your pump needs is a capacitor which stores energy and can be used in short bursts (just what the pump needs when it initially starts up... the same as an air conditioner). I am not sure if you could attach a capacitor external to the water pump (as an add-on) but it might be a feature to look for the next time you have to replace the water pump. Commented Sep 13, 2010 at 9:12
  • The load on the pump spin-up would take quite a cap/battery. My thought of a UPS was that the battery has a reserve of power, that would reduce the initial spin-up load. Some UPSs have this feature. I think the pump that replaces this one some day, will be a variable speed, which eliminates the need for a pressure tank, and greatly reduces the power needs.
    – MarkD
    Commented Sep 13, 2010 at 14:12

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