Hopefully, it's not a problem inside the unit that's causing the circuit breaker to trip. Is there another electrical appliance plugged into the same outlet or on that circuit that is ON and draws 15 amps of power? If so, that's the problem. If that's not the case, turn the circuit breaker OFF and remove the outlet cover, so you can inspect the receptacle and it's wiring. A loose wiring connection or a broken or cracked receptacle could be the issue. If you don't find any damage reassemble the outlet and turn the circuit breaker back ON. Instead of plugging in the dehumidifier, plug in a lamp or something similar and turn it ON. Leave it on for more than 5 minutes to see if the circuit breaker trips again. If it does, you'll know the problem is either with the outlet receptacle or the circuit breaker. If doesn't, plug in the dehumidifier (Make sure the Master ON/OFF Switch on the unit is in the OFF position, before plugging it in. Then turn the Master ON/OFF Switch to ON and set your controls. If the circuit breaker trips again, the problem is in the dehumidifier. You will need to call Whirlpool Customer Care, as it's an internal electrical issue.
In case you have misplaced your Owners Manual, I have included a link to it, that you can download and print for future reference. http://www.kitchenaid.ca/assets/pdfs/literature/Use%20and%20Care%20Guide%20-%201188927.pdf
I hope what information I have provided to you, will help you trouble shoot and solve the problem.