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Question DetailsAsked on 5/5/2017

lights slightly dim when dehumidifier kicks in

Hi, I have noticed that since I started using my dehumidifier some lights in the house slightly dim (It is so slight that at first I thought it was just my eyes until my wife said something) when the dehumidifier comes on. The dim is so quick it lasts less the 1 second and then everything is fine. The dehumidifier is on its own breaker on a 200 AMP circuit. I never noticed this issue until I started using the dehumidifier. Is it possible for a newer dehumidifier to cause this very slight and quick dim when starting up? Thank you.

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2 Answers


A decent sized dehumidifier can pull about 4-5 amps when running, but at startup can pull 7-10A commonly - which is definitely enough to cause a power flicker or second or less slight dimming of the lights. Similar to turning on a hair dryer or toaster or microwave will cause a momentary flicker in many cases.

The reason only some lights dim is the dehumidifier is undoubtedly 120v - so it is pulling off one side of the 240V main power feed to the house - circuits on the "other side" of the 240V feed (coming off the other "live" 120V wire in the 240V service) are not seeing that momentary demand on their feed wire so do not dim. (Circuits in a house are typically split about 50-50% between the two incoming 120V feeds).

When you say it is on a 200A circuit, I hope (and am pretty sure) that you mean 200A main breaker or main service, not its circuit. The breaker for the dehumidifier circuit should be rated for the dehumidifier circuit wire size, or if a dedicated circuit should be rated for the dehumidifier load itself at 125% of the full load operating amperage on the name plate - probably a 15A breaker (with 14 ga wiring, or 16 ga in some older houses) or maybe a 20A breaker (12 ga wire) for a large unit.

Answered 3 years ago by LCD



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Answered 3 years ago by Member Services

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