Why do lights flicker in our house when our dishwasher is running?
February 11, 2024 9:30 AM   Subscribe

Whenever our dishwasher is running, various lights in the house will flicker if they are on. The dishwasher is on its own circuit, and the offending lights (which all use LED bulbs) are on two different circuits, neither of which is the dishwasher's circuit. No other light fixtures in the house have this problem. What could be going on here, and how might we fix it?
posted by Mechitar to Home & Garden (7 answers total) 3 users marked this as a favorite
Step 1 would be to confirm that the dishwasher is indeed on its own circuit. If you throw the breaker for the dishwasher, are the lights in question (or, anything else for that matter) affected?

Second guess would be the dishwasher is spitting out interference that is affecting your lights. Even if devices are on separate circuits, they are all still essentially tied together at the service panel (which is why powerline Ethernet adapters will work across outlets that are on different breakers). It's not uncommon for an electric motor (or pump) to cause EM interference which affects other devices.

You could install an inexpensive EMI filter between the dishwasher and its power feed, and see if that helps. Depending on your local codes, this could be easy if your dishwasher is merely plugged into an outlet, or a bit more difficult if it's required to be hardwired to a junction box, but either way, filter options are available. Inline, wired-in EMI filters are $10-$20 depending on amperage rating (check your dishwasher's specs). The difficulty of the installation would be about on par with replacing a wired-in light fixture or outlet, along with similar safety precautions. Most filters come with standard push-on spade lugs, so a handful of connectors and a crimper will likely be needed. You may also need some short lengths of proper-gauge wire as well, so you have enough slack to safely and securely mount the filter, and still have enough reach to the junction box supplying power.
posted by xedrik at 9:54 AM on February 11 [3 favorites]

The dishwasher is on its own circuit, and the offending lights (which all use LED bulbs) are on two different circuits,

Are the LED bulbs the only consumers on those circuits, and do all the bulbs on those circuits show this flickering?

My initial suspicion is that the neutral feed for these three circuits (on the un-switched side of their respective circuit breakers), connects them together as it should, but has a marginal contact with the main neutral bus. All of this is inside the main breaker panel, so you might want to have an electrician take a peek inside of it and check things out.
posted by Stoneshop at 11:14 AM on February 11 [3 favorites]

Response by poster: Hey @Stoneshop, to respond to your question:
"Are the LED bulbs the only consumers on those circuits, and do all the bulbs on those circuits show this flickering?"

Circuit A: Has several outlets and lights on it. Of the lights, the ones that flicker use Edison-base LED bulbs (and one fixture with an incandescent flickers slightly). Lights on the circuit that DON'T flicker have an Edison-base incandescent-look LED bulb or GU10-base halogen bulbs. (There are a couple other lights on the circuit that I'm not sure about since they're rarely used).

Circuit B: Has a few lights and outlets on it. Of the lights (one of which is plugged into an outlet), two with Edison-base LED bulbs have the flicker problem (there's a third light I'm not sure about - haven't checked or noticed anything).
posted by Mechitar at 11:58 AM on February 11

Filament bulbs, so the normal incandescents and especially the halogen bulbs, have a certain thermal inertia so that any voltage dips don't immediately cause brightness dips. LED bulbs can be quite the mixed bag there, some don't show brief voltage dips at all, others do so enthousiastically. The incandescent-look LEDs apparently belong to the first group, and this is helped by the coating on the LEDs forming the 'filament'. But the fact that a normal incandescent flickers too implies there is an actual voltage drop, as they're almost totally insusceptible to EMI.

As I said, I strongly suspect there's a less than perfect connection somewhere in a common part for these three circuits. And when the dishwasher's pump or heater kicks in the increased current draw will cause a sufficiently large voltage drop across that connection that you'll see the lights flicker.

Electronic equipment on one of the two affected circuits will only rarely misbehave under such voltage dips; their power supplies have sufficient buffering to ride out even longer and deeper dips.
posted by Stoneshop at 2:26 PM on February 11 [1 favorite]

Could the offending bulbs be “dimmable” types, and they are interpreting the back emf of the motor as the classic chopped AC waveform of a dimmer, and briefly responding?
posted by nickggully at 5:03 PM on February 11

Do they flicker all the time when the dishwasher is on? Could the lights be on the same circuit as the hot water heated and the lights flicker when it turns on?

Another possibility is that two circuits share a leg. This can happen accidentally, but also in rare cases on purpose.
posted by Short End Of A Wishbone at 8:03 PM on February 11

I had something similar a few years back. It turned out to be corrosion on the connector to the line leading into our house (at the street end). Had to get the power company to diagnose & fix it.
posted by HiroProtagonist at 7:42 PM on February 13

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