The ground pin fell out of the plug to my dehumidifier. I tested and it still works. Is it dangerous for me to continue to use the dehumidifier?
They didn’t put the thing there for their health, they put it there for your safety. I would suggest, if you’re somewhat handy, replace the plug with something like this The only trick is to make sure each wire goes to the correct blade.
it is best that when you have a metal case for an appliance that the appliance be grounded, especially a dehumidifier which is likely used on a concrete floor.
replacement plugs can be purchased for 1 to 3 dollars. follow directions included with the plug to wire it correctly.
The grounding plug is there so that if something goes wrong (i.e. a short), the current won’t seek ground through you. However, not having the grounding plug does not do any damage to the appliance. I am not suggesting that you not replace the plug (that would be irresponsible), but many years ago I rented an apartment and after I had been there over a year I discovered that the outlets did not actually have a ground. They had the hole, mind you, it just wasn’t actually grounded. Now I test outlets using a device bought at the hardware store.
Sever the power cord near the plug and install a new plug. I would suggest using a high-quality plug, like something made by Hubbell.
Many accidents happen when 2-3 things go wrong. The pin is the first one. Replace the plug before the second happens. When will that be, maybe 10 years, maybe 10 seconds.
Thank you all very much. I will replace the plug.
A working Ground Fault Interrupter will save your life, even if an appliance’s ground connection is broken. (Or so Dopers assured me in a recent related thread.) I don’t know if such Interrupters are in common use in American homes, but they are necessities in countries like Thailand where faulty wiring and appliances are common.
Of course, as thelabdude implies, the Interrupter may itself fail, making you wish (if you’re still breathing well enough to wish) that you’d also fixed the plug.
I have a suspicion that my home may have the “fake” grounded outlets. The previous owner (first and only other) did some pretty freaky stuff with wiring to the detached garage and an outbuilding. The breaker box is poorly marked. Anytime I trip a breaker I make note of all the fixtures on that breaker. I googled the device you mentioned and will buy one and test the few (only 5 of 24 outlets in the house are 3 prong) that appear to be grounded.
But first…disconnect the plug from the electrical circuit…
the receptacles in the garage should be GFI (Ground Fault Interrupt) either with a circuit breaker in the breaker box or a GFI receptacle being the first in the string of them in the garage. the wiring feeding the garage should have a good grounding connection.
the out building, especially if it has dirt or concrete floor, should also be the same as the garage.
if you suspect some freaky stuff then it might be a good idea to read a book on home electricity, not that it would qualify you to do all the repairs on your own (people can read those books and still not know what they are doing or at least put it into practice correctly) but it will help you understand the issues even if you have to hire an electrician.
But that takes all the fun and challenge out of it. 
To elaborate on this a bit, in the U.S. you have three wires, hot, neutral, and ground. the neutral is grounded at the service entrance, which may make you wonder why you need a separate ground, but if you look at different failure types, you’ll see that a separate protective ground covers more fault scenarios. For example, if you had the old fashioned two prong plugs which only have hot and neutral and you ground the case of your humidifier to the neutral, if the neutral connection in the circuit breaks, the case of the humidifier will float up to 120 volts which can kill you. By having a separate protective ground, you insure that this won’t happen. And if you break the protective ground, you still have to have another fault along with it before the case becomes dangerous to touch. So the three wire system is definitely safer.
You’ve just lost your protective ground, so the case of your humidifier is no longer protected. It’s not going to be harmful to you unless another fault happens, so it’s not like it is going to kill you right away or anything. But since you have lost that protective ground, if the hot wire inside happens to short to the case (which sometimes happens - wires rub against surfaces over the years and sometimes wear through the insulation, for example) the case could become electrically hot and you wouldn’t know about it until you touched it and got shocked (and possibly killed).
So yeah, as others said, replace the plug. It’s a cheap fix.
GFIs (aka GFCIs, or ground fault circuit interrupters) have been required in places like kitchens, bathrooms, and garages for several decades now. In the past ten years or so, AFCIs (arc fault circuit interrupters) have been required in bedrooms. An AFCI will trip when it detects something like a frayed extension cord arcing, so they are really good at preventing fires.
There is no requirement in the U.S. to retrofit these devices into older homes, so homes built in the 1950s and earlier won’t even have the protective ground (they’ll just be two wire plugs), and homes built before the 70s will not usually have GFCIs in them unless the homeowner decided to retrofit them.
homes before the 1950s, even if two wire plugs, may have a grounding conductor if wired with metallic conduit or metallic cable.
homes with a grounding conductor but without GFCI are worth the retrofit. a $3 to $5 GFCI receptacle at the start of a string or receptacles in a kitchen, bath, basement, garage or outdoors will protect that string. a inexpensive potential lifesaver.
Very true. But it should also be mentioned that it doesn’t even have to be a “hard” short between hot and the metal chassis. A more common scenario is a significant decrease in resistance between hot and the chassis somewhere in the circuit, say from 20 MΩ to 10 kΩ. This is usually caused by insulation materials breaking down due to aging or overstress. A person (who is grounded) touching the chassis would definitely receive a shock. Connecting the chassis to ground at the CB panel would prevent such a scenario.