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I have a dehumidifier working 24/7 for about six months of the year. I've never moved it from the one outlet. Today the fuse keeps blowing. Nothing new is plugged in: no change whatsoever. I plug the dehumidifier in an other outlet, and all is well. Can someone explain what has happened?

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    Where are you on this planet? And are you talking about the fuse or breaker protecting the branch circuit, or a fuse or breaker inside the dehumidifier?
    – ThreePhaseEel
    Aug 24, 2017 at 11:39
  • The load on that cut hit could be larger than the one that did not trip or the new circuit a 20a vs a 15 on the original circuit. 6 years old has the unit been serviced bearings do need grease , oil depending on the type as they age the unit starts drawing more power.
    – Ed Beal
    Aug 24, 2017 at 14:19
  • Something else has been added to that circuit. When houses are wired with fuses, they typically have a great many receptacles/outlets sharing a single fuse. Something else has been added elsewhere in the house, and it together with the dehumidifier is now overloading the circuit.
    – Harper - Reinstate Monica
    Aug 24, 2017 at 17:54

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When you say you have not plugged anything new in, I take it that you have not bought any new appliances or electronic gadgets. In addition, you stated that the dehumidifier functions just fine when plugged into another outlet. If that is indeed the case then read on.

I have seen something similar occur twice in both residential and industrial settings. What may be happening is a bad connection in the wiring is causing a voltage drop. The bad connection might only affect that one outlet, the whole circuit or part of a circuit.

A small load like a lamp or phone charger will function properly and a voltmeter will show the outlet/circuit as good. But a larger load like a vacuum cleaner or dehumidifier will draw enough current to drop the voltage down enough to where the motor can't get up to speed causing it to pull lots of current. The breaker can't handle the higher current so it trips.

Try this test:

  1. Unplug the dehumidifier from the suspect outlet.
  2. Plug a lamp with an old school incandescent bulb into a different, known working outlet. Note the brightness of the lamp.
  3. Now move and plug the lamp into the suspect outlet. Turn the lamp on and let it sit for a few minutes and note the brightness. The lamp should glow brightly and the circuit breaker should not trip. NOTE: This will NOT reliably work with a compact fluorescent (CFL) or LED bulb.

If the breaker trips or you immediatly notice that the lamp is glowing dimmer in the suspect outlet than the good outlet, you have a wiring problem. If the lamp works fine then proceed below...

  1. Plug the dehumidifier into the suspect outlet ALONG WITH the lamp and turn it on. Make sure the lamp is on before you switch on the dehumidifier. Watch the brightness of the lamp. If the lamp goes dim and stays dim until the breaker trips, you have a voltage drop indicating a wiring problem.

If you have a voltmeter, you can use that in place of the lamp. You can also try using a vacuum cleaner in place of the dehumidifier for step 4.

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  • I was going o provide the same answer this morning, except that in this particular case I would turn off the breaker and remove and inspect the outlet regardless. Also, is the house aluminum wiring? Also, what else is powered off when the breaker/fuse trips? Those other things are possible areas of a bad connection if the outlet isn't it.
    – noybman
    Aug 24, 2017 at 22:25

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