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I have an HP consumer-sized color laser printer. (M255dw). I plugged into a GFCi receptacle that protects outside outlets wired to its output terminals.

Every so often, it tripped when the printer started up. I unplugged everything else from the circuit; same result. I replaced the outlet. Same result. I called up HP, and said, 'hey, this printer has a ground fault'. The HP safety person and I were both a bit puzzled as to how this could be, but they sent me a new one.

Guess what happened this morning, which happens to be a damp morning here in damp Seattle. Printer started up, ground fault tripped.

What have we got here? Is there some reason why the surge current of the printer starting up would trip the ground fault? Or could there be a problem with the outdoor outlets?

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  • Have you tried the printer on another outlet, different circuit? – JACK May 2 '20 at 17:40
  • Does the outlet trip if you substitute a different load for the laser printer? – ThreePhaseEel May 2 '20 at 17:42
  • Try plugging the printer into a different GFCI protected circuit. These can be reliably found in kitchens and bathrooms (or at least should). Also make sure you are dealing with GFCI and not AFCI. Very different things. – Harper - Reinstate Monica May 2 '20 at 17:52
  • GFCIs go bad for a variety of reasons all the time. Given your circumstances, my guess is that your outlet is faulty. – Aloysius Defenestrate May 2 '20 at 18:13
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I agree that a badly designed product is an improbability, since it is not a refrigerator, freezer or garage door opener. Big motor driven things tend to give GFCIs fits. The big load in a laser printer is the fuser heater, a resistive load that has no inductive kick.

So I think it boils down to one of two cases:

  • The circuit is already almost tripping the GFCI due to other pre-existing ground faults, and something about the laser printer (power factor?) is the straw that broke the camel's back. I would expect this sort of thing to improve or get worse with dry/rainy weather. The fix would be open up and clean out those outdoor outlets, get all the dust, old leaves and rocks out of the boxes, dry them out, and then get a better outdoor cover. (how do rocks get in there anyway?)

  • The GFCI is marginal to begin with, and the printer is too much for it for some reason. You'd need to pause to distinguish it from the first case, and then if necessary, replace the GFCI. I would do this reluctantly.

  • Or, if the printer is plugged into a location that was previously unused, it is miswired (half-in, half-out of that GFCI's protection).

Either way, the proof of the pudding will be to relocate the printer to another GFCI circuit, and see if the problem moves with it. Meanwhile put other hungry heating loads on that receptacle.

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  • I already replaced the GFCi, FWIW. I'll have a look at the outdoor outlet. – bmargulies May 3 '20 at 4:08
  • Well, now you've got a spare one. Put it to good use protecting a basement, garage, laundry room etc. circuit. Anywhere water can be. – Harper - Reinstate Monica May 3 '20 at 5:52
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The HP M255dw laser printer shows online to be a wireless capable product. I suggest that due to its portability you temporarily relocate the printer to a completely different circuit so you can determine if the printer does cause these trips or not.

You should test both on a GFCI protected circuit and one that is not protected.

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  • I have moved it to another circuit. Now the circuit it was on is unused. I really don't have anything else handy to use it for. – bmargulies May 3 '20 at 4:08

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